Canadian Geographic Explorer/Canadian Geographic Explorer.iso/pc/comp.z/GLOSSARY.HLP

Text File | 1996-05-01 | 130.9 KB | 4,341 lines

1    Absolute value
@keyword{Absolute value}

 A method of creating essentially all colours through the addition
 of light of the three additive colour primaries (blue, green, and red)
 in various proportions through the use of three separate projectors.


1    Additive colour process
@keyword{Additive colour process}

 A method of creating essentially all
 colours through the addition of light of the three additive colour
 primaries (blue, green, and red) in various proportions.


1    Aerial photograph, oblique
@keyword{Aerial photograph oblique}

 A photograph taken with the camera axis directed between the horizontal
 and vertical (1) high oblique: an oblique photograph in which the
 apparent horizon is shown. (2) low oblique: an oblique photograph in
 which the apparent horizon is not shown.


1    Aerial photograph, vertical
@keyword{Aerial photograph vertical}

 An aerial photograph made with the optical axis of the camera
 approximately perpendicular to the Earth's surface and with the
 film as nearly horizontal as practicable.

1    Aggregation, class
@keyword{Aggregation aggregate merge}

 The merging of distinct thematic classes into a single
 combined unit or class.


1    Albedo
@keyword{Albedo}

 (1) The ratio of the amount of electromagnetic radiation reflected by
 a body to the amount incident upon it, often expressed as a percentage,
 e.g. the albedo of the Earth is 34 percent. (2) The reflectivity of a body
 as compared to that of a perfectly diffusing surface at the same distance
 from he Sun, and normal tot he incident radiation.


1    Albers equal area projection
@keyword{Albers equal area projection}

 A conical projection characterized by two standard parallels of latitude
 along which the scale is correct. The meridian and parallels are
 constructed in inverse proportion in order to maintain an equal
 area representation.


1    Algorithm
@keyword{Algorithm}

 (1) A fixed step-by-step procedure to accomplish a given result;
 usually a simplified procedure for solving a complex problem; also a full
 statement of a finite number of steps. (2) A computer-oriented procedure
 for resolving a problem.


1    Alphanumeric
@keyword{Alphanumeric}

 A character set composed of letter, integers,
 punctuation marks, and special symbols. Usually the number of
 characters in a set varies between forty-eight and sixty-four.


1    Alphanumeric
@keyword{Alphanumeric}

 A character set composed of letters, numbers, punctuation
 marks, and special symbols. Usually the number of characters in a
 set varies between forty-eight and sixty-four.


1    Altitude
@keyword{Altitude}

 Height of a sensor platform above a datum; the datum is usually
 mean sea level.


1    Amplitude
@keyword{Amplitude}

 Amplitude format is the most common format for SAR (Synthetic Aperture Radar)
 data to be delivered in. When filtering SAR data you can select either
 Amplitude or Power format.  Amplitude data is the square root of Power
 format.  Power is the same as intensity format.  Also see POWER.


1    Anaglyph
@keyword{Anaglyph stereo}

 A stereoscopic diagram in which the two views are printed or
 projected superimposed in complementary colours - red and blue.
 By viewing through spectacles of corresponding complementary colours,
 the user can form a stereoscopic image.


1    Analog
@keyword{Analog analogue}

 A continuously varying electronic signal (contrast with digital).


1    Ancillary data
@keyword{Ancillary data}

 In remote sensing,secondary data pertaining to the
 area or classes of interest, such as topographical, demographic, or
 climatological data. Sometimes pertains to sensor data such as
 altitude, attitude, time or calibration that often accompanies image
 data. Ancillary data may be digitized and used in the analysis process
 in conjunction with the primary remote sensing data.


1    And
@keyword{and logical}

 A binary logical operator that is assigned the value true only if both
 of its operands are true.


1    Anotate
@keyword{Annotate annotation}

 In EASI/PACE, text generated in a graphic plane of ImageWorks
 using the EDIT-GRAPHIC option.

 See also Annotation.


1    Annotation
@keyword{Annotate annotation}

 In EASI/PACE, text or graphics added to the surround of a map which help
 to orient the user. Titles, subtitles, legends, framed borders, and
 longitude/latitude graticules or projection grids are all kinds of annotation.


1    ANSI
@keyword{American National Standards Institute ANSI}

 An association formed by the American government and industry to
 produce and disseminate widely used industrial standards.


1    Append
@keyword{Append add}

 To add elements to the end of a sequentially organized data structure
 such as a character string, a list, a queue, or a sequential file.


1    Archival storage
@keyword{Archival storage archive backup save copy}

 Magnetic media (tapes, removable disks) used to store programs and
 data outside the normal addressable memory units of the computer.


1    Array
@keyword{Array matrix}

 A series of addressable data elements in the form of a grid or matrix.


1    ASCII
Akeyword{ASCII}

 Acronym for American Standard Code for Information Interchange, is
 a widely recognized assignment of numeric codes to printable characters
 and certain device control codes. ASCII files, also called text files,
 can be printed or viewed directly on-screen.


1    Aspect
@keyword{Aspect orientation}

 The horizontal direction in which a slope faces, commonly expressed
 in degrees clockwise from north (top of image). A west-facing slope
 (towards left side of image), for example, would have an aspect of
 270 degrees.


1    Aspect ratio
@keyword{Aspect ratio}

 The ratio of width to height for a computer display or, more
 generally, for any projected image. A 2000 by 1500 raster image,
 for example, has a 4:3 aspect ratio. Loading this image to a display
 window with an aspect ratio of anything other than 4:3 would result in
 a distorted image.


1    Attitude
@keyword{Attitude}

 The angular orientation of a sensing system with respect to a
 geographical reference system.


1    Attribute
@keyword{Attribute}

 A list of numeric and/or character data associated with a numeric
 code. These lists are stored on a PCIDSK database in text segments (TYPE
 140:TEX). The numeric code is always a grey value (or range of values)
 with a particular image channel stored on the PCIDSK database.


1    AUTOEXEC.BAT
@keyword{AUTOEXEC.BAT startup}

 The reserved name of an MS-DOS batch file invoked
 automatically on system startup. An AUTOEXEC.BAT file should contain
 commands needed to (1) initialize the environment by setting MS-DOS
 options and parameters; (2) verify that the fixed disks are undamaged
 and have sufficient free space for normal operation; (3) invoke any
 permanently resident utility programs; (4) establish any linkage to the
 local area network (LAN); and (5) transfer control to any control program
 such as DOSSHELL, Windows, or DesqView.


1    Azimuth
@keyword{Azimuth}

 The geographical orientation of a line given as an angle measured
 clockwise from north.


1    Azimuthal equal area projection
@keyword{Azimuthal equal area projection}

 An azimuthal projection where because of its spacing of parallels
 which decreases with increasing distance from the centre thus provides
 an equal area representation.


1    Azimuthal projection
@keyword{Azimuthal projection}

 A projection constructed as if a plane was to be placed tangential to
 the surface of the earth and the surface were then transferred onto
 the plane. Thus, all points have a true azimuth.


1    Background processing
@keyword{Background processing}

 Tasks not requiring direct user interaction are assigned a lower
 priority by the computer.

 In EASI/PACE a task can be assigned this lower priority by selection
 of the `RUNBACK' command button in Xpace program panels.


1    Backspace
@keyword{Backspace delete}

 To delete the character immediately to the left of the cursor (or to
 the left of the last character typed) by pressing the Backspace key
 located in the upper-right corner of most keyboards.


1    Back-up
@keyword{Back-up save archive copy}

 Making a copy of a file or a whole disk for safe keeping in case the
 original is lost or damaged.


1    Band
@keyword{Band}

 (1) A Selection of wavelengths. (2) Frequency band. (3)
 Absorption band. (4) A group of tracks on a magnetic drum. (5) A
 range of radar frequencies, such as X-band, Q-band etc. (6) An image
 plane within a PCIDSK file.


1    Bandwidth
@keyword{Bandwidth}

 (1) In an antenna, the range of frequencies within
 which its performance, with respect to some characteristic,
 conforms to a specified standard. (2) In a wave, the least
 frequency interval outside which the power spectrum of a
 time-varying quantity is everywhere less than some specified
 fraction of its value at a reference frequency.  (3) The number
 of cycles per second between the limits of a frequency band.


1    Bar scale
@keyword{Bar scale}

 A graduated line on a map, plan, photograph, or mosaic, by means
 of which actual ground distances may be determined.


1    Base, photo
@keyword{Base photo}

 The distance between the principal points of two adjacent prints
 of a series of vertical aerial photographs. It is usually measured on
 one print after transferring the principal point of the other print.


1    Batch processing
@keyword{Batch processing}

 The method of data processing in which data and programs are entered into
 a computer which then carries out the entire processing operation with no
 further instructions.


1    Baud rate
@keyword{Baud rate BPS}

 A measure of the speed of data transmission between a computer
 and other devices - equivalent to bits per second.


1    BIL (Band Interleaved by Line)
@keyword{BIL Interleaved}

 A method of image data storage wherein the first line of the first band
 of imagery is stored, followed by the first line of the second band,
 and so on. This storage format is repeated for the second and subsequent
 lines of the image bands involved.


1    Bimodal
@keyword{Bimodal}

 See Also: {|}Mode


1    Binary
@keyword{Binary Bit}

 Having two possible values or states. These two states have no
 inherent value until interpreted, whether by people or machines.
 Depending on the context, they may be interpreted in different ways:
 0/1, on/off, true/false, yes/no, closed/open, positive/negative.

 See also: {|}bit


1    BIP (Band Interleaved by Pixel)
@keyword{BIP Band Interleaved}

 A method of image data storage wherein the first pixel of the first
 band of imagery is stored, followed by the first pixel of the second
 band, and so on. This storage format is repeated for the second and
 subsequent pixels of the image bands involved.


1    Bit
@keyword{Bit binary}

 Abbreviation for binary digit; a number that can take only the values
 0 or 1.

 See also: {|}Binary


1    Bitmap
@keyword{Bitmap}

 (1) A one bit deep graphic mask. (2) A (0,1) matrix, i.e.,
 an image plane wherein each pixel is either 0 (off) or 1 (on).


1    Bitplane
@keyword{Bitplane}

 See Also: {|}Bitmap, {|}Graphic Plane


1    Bitwise operators
@keyword{Bitwise operators}

 The set of machine instructions or programming language
 facilities designed to manipulate bit-oriented data. These include
 the logical operations (and, or, xor, or not), shift and rotate
 instructions, and masking instructions.

 See also: {|}Boolean operator

1    Blackbody
@keyword{Blackbody}

 Theoretical object that is both a perfect absorber and a perfect
 radiator or emitter; its emissivity is 1. All other bodies (greybodies)
 are less efficient absorbers and radiators, and their emissivities
 are always less than 1.


1    Boolean Operator
@keyword{Boolean Operator}

 A logical function use to establish true/false conditions.  Includes
 AND, OR, XOR (Exclusive OR), NOT and so forth.

1    BPI (Bits Per Inch)
@keyword{BPI}

 The density of bits recorded on a magnetic tape. 800, 1600, and 6500
 are common standards.


1    Brightness
@keyword{Brightness}

 The attribute of visual perception in accordance with
 which an area appears to emit more or less light.


1    BSQ (Band Sequential Interleaving)
@keyword{BSQ Sequential Interleaving}

 A method of image data storage wherein the first band of imagery is
 stored in its entirety, followed by the entire second band, and so on.
 This storage format is repeated for all subsequent bands involved.


1    Bug
@keyword{Bug error}

 An error in a program or computer system.


1    Button
@keyword{Button}

 In a graphical user interface (GUI), an object on the screen that the
 user can select, either by a mouse click or by an equivalent keyboard
 operation, to trigger a specified action or response by the software.
 Program designers use buttons to give an effect like pushing a physical
 button on a control panel. Typically, graphics are used so that buttons
 being chosen appear to be physically pressed. Some buttons may include
 special text or pictures (icons) that make them easy to recognize.


1    Byte
@keyword{Byte}

 A sequence of 8 bits, representing 256 integer values ranging from 0 to
 255.


1    Cadastre
@keyword{Cadastre survey}

 A survey that creates, defines, retraces, or reestablishes the
 boundaries and subdivisions of public lands and private estates.
 The ownership and value of private lands are recorded for taxation.


1    Carriage return
@keyword{Carriage return enter}

 A distinct ASCII character, commonly used to end a printed
line or data record. The keyboard location of this instruction is often
labelled return or enter.


1    Case-sensitive
@keyword{case-sensitive}

 A characteristic of programs and operating systems that
 determines whether uppercase (capital) letters are treated differently from
 lowercase letters. UNIX commands are case-sensitive. However, MS-DOS
 commands are not, so that, for example, to display a directory, you can enter
 dir, DIR, Dir, and so on. Some text editors and word processors offer case-
 sensitivity as a user-selected operating mode.


1    Category
@keyword{Category}

 See Also: {|}Class


1    Cathode ray tube (CRT)
@keyword{Cathode ray tube (CRT)}

 A vacuum tube capable of producing a
 black-and-white or colour image by beaming electrons onto a
 sensitized screen. As a component of a data-processing system,
 the CRT can be used to provide rapid, pictorial access to
 numerical data.


1    CCT
@keyword{CCT}

 See Also: {|}Computer-compatible tapes


1    CD-ROM
@keyword{CD-ROM}

 Acronym for compact disk, read-only memory, it is an optical
 storage medium identical to the digital disks used for musical recordings.
 A CD-ROM disk can store about 650M of data.


1    Cell
@keyword{Cell pixel}

 The basic element of spatial information in the raster (grid) description
 of spatial entities.

 See also: {|}pixel


1    Central meridian
@keyword{Central meridian}

 The line of longitude upon which a map projection is constructed.


1    Central tendency
@keyword{Central tendency}

 Statistical measures which indicate the average of a set of
 observations. Measures of central tendency include the mode, median, and
 arithmetic mean.


1    Centroid
@keyword{Centroid}

 In EASI/PACE, a point placed inside of a polygon to which the
 attributes of the polygon can be associated.


1    Change-detection images
@keyword{Change-detection}

 Images prepared by digitally comparing
 two original images acquired at different times. The grey tones
 of each pixel on a change-detection image portray the amount of
 difference between the original images.


1    Channel
@keyword{Channel}

 See also: {|}Band


1    Class
@keyword{Class}

 A surface characteristic type that is of interest to the
 investigator, such as forest by type and condition, or water by
 sediment load. Each unit is assumed to be of one and only one given
 type.  The set of types is called the set of "classes" or
 "categories," each type being a particular category. The categories
 are chosen specifically by the investigator as being the ones of
 interest to them.


1    Classification
@keyword{Classification}

 The process of assigning pixels from a multispectral image to classes,
 generally on the basis of spectral reflectance characteristics.


1    Click
@keyword{click}

 The action of pressing and quickly releasing a button on a mouse or
 similar pointing device. Clicking is always directed at some object shown
 on  the screen. The usual terminology is to \`click on\' the object;
 that is, to click while the mouse pointer on the screen is touching the
 object.

 By convention in many graphical user interfaces (GUI) systems and
 applications, a single-click simply selects an object, whereas a rapid
 double-click activates an object.


1    Clipping
@keyword{Clipping}

 The shearing off of the peaks of a signal. This may
 affect either the positive or negative peaks, or both.


1    Clustering
@keyword{Clustering}

 Any of a set of algorithmic techniques that processes
 a set of data (e.g., an image) to determine groups or clusters of
 data points based on a statistical measurement of some sort.
 Misunderstanding of the preparation for and use of clustering is the
 greatest single source of analysis error in remote sensing image
 analysis.


1    Colour
@keyword{Colour}

 The property of an object which is dependent on the
 wavelength of the light it reflects or, in the case of a
 luminescent body, the wavelength of light that it emits. If, in
 either case, this light is of a single wavelength, the colour
 seen is a pure spectral colour; but if light of two or more
 wavelengths is emitted, the colour will be mixed. White light is
 a balanced mixture of all the visible spectral colours.


1    Colour balance
@keyword{Colour balance}

 The proper intensities of colours in a colour
 print, positive transparency, or negative, that give a correct
 reproduction of the grey scale (as faithful as can be achieved
 by photographic representation of a true colours of a scene).


1    Colour composite (multiband photography)
@keyword{Colour composite (multiband photography)}

 A colour picture
 produced by assigning a colour to a particular spectral band.  In
 Landsat, blue is ordinarily assigned to MSS band 4(0.5-0.6 um),
 green to band 5 (0.6-0.7 um), and red to band 7(0.8-1.1 um), to
 form a picture closely approximating a colour infrared
 photograph.


1    Command mode
@keyword{Command mode interface}

 A method of specifying commands via the keyboard entry of keywords and
 arguments, rather than through the selection of items from a menu or button
 from a GUI. In EASI/PACE, the command mode is called EASI.

 See also Menu mode and GUI.


1    Complementary colours
@keyword{Complementary colours}

 (1, optics) Two colours are complementary
 if, when added together (as by projection), they produce
 neutral-hue light. (2) Colours of pigment which when mixed
 produce a grey.


1    Complex number
@keyword{Complex number}

 A superset of the real numbers, with a real and imaginary
 component. A complex number is written as a + bi, where i is defined
 as the square root of -1.


1    Compression
@keyword{Compression}

 A class of mathematical transformations for digital data in
 order to minimize storage requirements or transmission time.


1    Computer-compatible tapes
@keyword{Computer-compatible tapes}

 Tapes containing digital data.
 These are standard magnetic tapes in 9-track format.


1    CONFIG.SYS
@keyword{CONFIG.SYS startup}

 An MS-DOS ASCII file containing parameters and commands
 that specify the physical or logical configuration of the computer
 and certain options chosen by the user.

 Some software products requires specific CONFIG.SYS values, and their
 install (or setup) programs may actually modify the user's MS-DOS
 CONFIG.SYS file. Although this practice relieves the user from having to
 know about and enter these values, it can occasionally lead to conflicts.


1    Conic projection
@keyword{Conic projection}

 A map projection constructed by projecting geographic meridians and
 parallels on to a cone which is tangential or intersects the surface
 of a sphere, with the cone touching one or more standard parallels.


1    Constant
@keyword{Constant}

 A word in memory identified by a label in th progrm and, in contrast
 to a variable, assigened a value that does not change during the
 execution of a program.


1    Context-sensitive help
@keyword{Context-sensitive help}

 Any help facility that takes note of what the user was doing just
 before asking for help and attempts to provide information relevant
 to that situation.

 Help in Xpace is context-sensitive.


1    Contour
@keyword{Contour}

 An imaginary line all points of which are at the same elevation.


1    Contrast stretching
@keyword{Contrast stretching}

 Improving the contrast of images by digital
 processing. The original range of digital values (grey-levels) is
 expanded to utilize the full contrast range of the recording film or
 display device.


1    Control, ground
@keyword{Control, ground}

 (1) Control obtained by ground surveys as
 distinguished from control obtained by photogrammetric
 methods; may be for horizontal or vertical control, or both. (2)
 Ground (in-situ) observations to aid in interpretation of remote
 sensor data.

 See Also: {|}Ground data, {|}Ground information, {|}Ground truth

1    Coordinates, geographical
@keyword{Coordinates, geographical}

 A system of spherical coordinates for
 describing the positions of points on the Earth. The
 declinations and polar bearings in this system are the latitudes
 and longitudes, respectively.


1    Corner reflector
@keyword{Corner reflector}

 An adjacent smooth surface which causes a double reflection of a
 radar signal, yielding a very high return. Because corner
 reflectors generally cover only small areas of the scene, they often
 appear as bright \`sparkles\' on a radar image.


1    Cosine
@keyword{Cosine}

 The ratio between the side adjacent to a specified acute angle in a right
 angled triangle and the hypotenuse.


1    Covariance
@keyword{Covariance}

 The measure of how two variables change in relation
 to each other (covariability). If larger values of Y tend to be
 associated with larger values of X, the covariance will be
 positive. If larger values of Y are associated with smaller
 values of X, the covariance will be negative. When there is no
 particular association between X and Y, the covariance value
 will approach zero.


1    CPU
@keyword{CPU}

 An acronym for central processing unit, the part of the computer that
 controls the flow of data nd performs the computations.


1    CRT
@keyword{CRT}

 An acronym for cathode-ray tube, which is similar to a television picture
 tube, on which an image is displayed by a pattern of glowing spots produced
 by directing a beam of electrons at a phosphorescent screen.


1    Cultural features
@keyword{Cultural features}

 All map detail representing man-made elements
 of the landscape.


1    Current directory
@keyword{Current directory}

 A directory (either the root directory or a subdirectory) that
 is taken as the default in subsequent reference (by a program or command)
 to a given disk drive.


1    Cursor
@keyword{Cursor}

 A conspicuous symbol on a computer screen showing the exact
 position at which the next keystroke or mouse click will take effect.


1    Cut and paste
@keyword{Cut paste edit}

 The process of selecting and removing a section of text or a
 graphic image from a file displayed on-screen and then inserting
 it in another file or in another part of the same file.


1    Cylindrical projection
@keyword{Cylindrical projection}

 A projection constructed as if the globe is inserted within a cylinder
 and the surface is then projected to the cylinder. Meridians and
 parallels are drawn as straight lines intersecting at right angles.


1    Data
@keyword{Data}

 Raw facts, often used as input to a program or an application system.


1    Data bank
@keyword{Data bank}

 A well-defined collection of data, usually of the
 same general type, which can be accessed by a computer.


1    Database
@keyword{Database}

 The collection of permanently stored data used by one or more
 application systems.

 EASI/PACE uses a database structure known as PCIDSK.

 See Also: {GDB|Sup|}PCIDSK

1    Data dimensionality
@keyword{Data dimensionality}

 The number of variables (e.g. channels)
 present in the data set. The term "intrinsic dimensionality"
 refers to the smallest number of variables that could be used to
 represent the data set accurately, e.g., principal components.


1    Data reduction
@keyword{Data reduction}

 Transformation of observed values into useful,
 ordered, or simplified forms.


1    Datum
@keyword{Datum}

 A geographical quantity which serves as a base or reference point for
 earth dimension models.


1    Decimal
@keyword{Decimal}

 The common numbering system using 10 as its base.

 EASI/PACE offers a decimal data type channel for image storage in order to
 avoid imprecision generated when fractional values are converted between
 decimal and binary.


1    Decision rule (or classification rule)
@keyword{Decision rule (or classification rule)}

 The criterion used to establish discriminant functions for
 classification (e.g.  nearest-neighbor rule, minimum-distance-to-means
 rule, maximum-likelihood rule).


1    Default value
@keyword{Default value}

 A value assigned to an input data item when the user does not enter
 any overriding value. If default values are used judiciously, a program
 can free the user from having to: (1) re-enter options, parameters, and other
 data that do not change from run to run; (2) enter information that merely
 confirms the choices that most users prefer; (3) know about the existence of
 rarely used options.

 In EASI/PACE, parameters not indicated by MISSING a default value if
 none is explicitly entered by the user.


1    DEM (Digital Elevation Model)
@keyword{DEM Digital Elevation Model}

 A file with terrain elevations recorded for the intersections of a
 fine-grained grid, commonly obtained with an orthophotoscope and
 organized by quandrangle as the digital equivalent of the elevation
 data on a topographic base sheet.


1    Density slicing (digital)
@keyword{Density slicing (digital)}

 The process of converting the continuous
 grey-levels of an image into a series of density intervals, or slices,
 each corresponding to a specific range of digital values.


1    Device
@keyword{Device}

 A name representing a physical or logical hardware component to the
 computer system. For instance, on MS-DOS and UNIX systems, the CON
 device represents the console (video monitor and keyboard), and the PRN
 device represents the printer. Devices can be used to designate the source
 of input or the destination of output from other commands or programs.


1    Device driver
@keyword{Device driver}

 A program, usually considered part of an operating system, that
 provides an interface between a particular kind of hardware device and
 the rest of the operating system.

 Device drivers localize knowledge of the detailed characteristics of a
 device so that application programs can use a wide range of functionally
 similar devices in a simple and s standard way.

 Drivers come from several sources: (1) drivers for widely used, standard
 devices are usually included in the operating system, as distributed by the
 software vendor; (2) drivers for new or unusual devices are provided by the
 hardware vendor; (3) software products, such a sword processors, designed to
 operate under MS-DOS or another small operating system, amy include their
 own drivers, especially for supporting a wide range of printers.

 MS-DOS includes several standard device drivers, such as HIMEM.SYS (an
 XMS memory driver), EMM386.SYS (an EMS memory driver), RAM disks,
 and cache programs. The CONFIG.SYS file specifies which of these drivers is
 to be loaded and activated.


1    Desktop
@keyword{Desktop}

 A metaphor in graphical user interface (GUI) systems to suggest a
 correspondence between managing icons and windows on a screen and
 arranging real objects on one's desk.


1    Dialog box
@keyword{Dialog box}

 A window that a program displays to prompt a reply from the user.


1    Digital
@keyword{Digital}

 The ability to represent data in discrete, quantized units or digits.


1    Digital image
@keyword{Digital image}

 A two-dimensional array of small areas called picture elements
 or pixels that correspond spatially to relatively small ground areas called
 ground resolution cells.


1    Digital tablet
@keyword{Digital tablet}

 A device used to determine and communicate to a computer the
 coordinates of points designated with a stylus. Locations are sensed
 electronically by the stylus and a tablet bed on which a graphic image or
 instruction menu is placed.


1    Digitization
@keyword{Digitization}

 The process of converting an image recorded
 originally on photographic material into numerical format.


1    Digitizer
@keyword{Digitizer}

 A device for converting point locations on a graphic image to plane
 (x,y) coordinates for digital processing.


1    Direct access file
@keyword{Direct access file}

 A file whose records can be accessed by location within the file,
 independent of the location of the most recently accessed record.
 Direct access files are almost always implemented on disk units.


1    Directory
@keyword{Directory}

 A list of file names, used in file management subsystems of operating
 systems. In many systems (including MS-DOS, VAX VMS, UNIX and OS/2)
 directories forma hierarchy. Each directory can contain both lower-
 level directories and file names. Some operating systems call directories
 catalogs or folders.


1    Discriminant function
@keyword{Discriminant function}

 One of a set of mathematical functions
 which are commonly derived from training
 samples and a decision rule, and are used to divide the
 measurement space into decision regions.


1    Disk
@keyword{Disk}

 The most common auxiliary storage medium for all types of computer
 systems. The term usually refers to a magnetic disk, but newer technologies
 such as optical disks, offer even higher capacity.

 As disks rotate, the read-write heads positioned over the disk can read
 information from any track quickly. Like all magnetic media, disks can
 be read from, written to, and erased repeatedly.


1    Disk drive
@keyword{Disk drive}

 A storage device that contains, rotates, reads, and writes a
 magnetic or optical disk. The disks can be either permanently mounted within
 the disk drive (a fixed disk) or removable (a floppy disk).


1    Diskette
@keyword{Diskette}

 See also: {|}floppy disk


1    Dispersion
@keyword{Dispersion}

 Statistical measures of the variability or spread of a set of observations.
 In some cases, values are tightly clustered around the average position,
 while in other cases they are dispersed over a wide range. Measures
 of dispersion include the range, standard deviation and variance.


1    Displacement
@keyword{Displacement}

 Any shift in the position of an image on a photograph that does not
 alter the perspective characteristics of the photograph (i.e., shift due
 to tilt of the photograph, scale change in the photograph, and relief of
 the objects photographed).


1    Display
@keyword{Display}

 Any output device that produces a visible representation
 of a data set for quick visual access; usually the primary hardware
 components are a large amount of memory with an accompanying monitor.


1    Distortion
@keyword{ Distortion}

 Any shift in the position of an image on a photograph which alters
 the perspective characteristics of the photograph. Causes of image
 distortion include lens aberration, differential shrinkage of film
 or paper, and motion of the film or camera.


1    Distribution function
@keyword{Distribution function}

 The relative frequency with which different values of a variable occur.


1    Dithering
@keyword{Dithering}

 The technique of placing a number of carefully selected colours (or black
 dots) in a rectangular dot matrix in order to simulate subtle shades (or
 grey tomes).

 In EASI/ACE, the hardcopy printing programs of the Map Output Package are
 designed for dithering type printers.


1    Documentation
@keyword{Documentation help}

 The written specifications of a program indicating the
 program's goals, memory requirements, data structures, and algorithms;
 the description and format for the data to be entered; and the description
 and format of the results.


1    Dot-matrix printer
@keyword{Dot-matrix printer}

 An impact printer utilizing a pattern of dots to form characters and
 graphics on paper. This inexpensive device, which is still widely used,
 uses one or two columns of pins, striking the paper through a ribbon
 saturated with ink; the more pins used, the sharper the printed image.

 Dot-matrix printers commonly are available in 9-, 18- and 24-pin
 configurations. (Laser printers provide better quality and much quieter
 operation than dot-matrix printers, usually at higher initial and operating
 costs.)


1    Double-click
@keyword{Double-click}

 To click the mouse button twice very quickly. The double-click
 is used to invoke applications under many graphical user interfaces (GUI).

 EASI/PACE applications are activated by a single-click action. Double
 clicking will cause two applications to startup.


1    Double precision
@keyword{Double precision}

 A floating-point number requiring two words eight bytes).
 In many implementations, double precision offers precision equivalent to 16
 decimal digits, instead of only 6 provided by single precision.


1    DN
@keyword{DN}

 Acronym for digital number; the numeric value assigned to a given pixel
 within a raster image.


1    Drag and drop
@keyword{Drag drop}

 The action of using a mouse to select and move an object or icon on a
 graphical user interface (GUI) system. tHe icon representing the
 object moves on the screen with the mouse cursor as long as the mouse
 button  is pressed. When you release the mouse button, the object is
 dropped onto its destination.


1    Drainage basin
@keyword{Drainage basin}

 That part of the land which is drained by a unitary river system.


1    Drainage divide
@keyword{Drainage divide}

 The ridge which separates neighbouring watersheds or basins.


1    Drift
@keyword{Drift}

 (1) The horizontal displacement of an aircraft, caused by
 the force of wind, from the track it would have followed in still air.
 (2) Slow, continuous change(s) in the distribution of a variable over
 time or space.


1    Dynamic range
@keyword{Dynamic range}

 (1) The ratio of maximum measurable signal to minimum
 detectable signal. (2) Minimum value to maximum value of a variable.


1    EASI
@keyword{EASI}

 The Engineering Analysis and Scientific Interface; PCI's
 user interface environment.


1    Edge
@keyword{Edge}

 The boundary of an object in an image, usually characterized by a
 rather drastic change in the grey shade value from the immediate
 interior of the boundary to the immediate exterior of the boundary.


1    Edge enhancement
@keyword{Edge enhancement}

 Any analytical technique that sharpens object boundaries in an image.


1    Edit
@keyword{Edit}

 To remove errors from, or to modify a computer file of a program, a
 digitized map or a file containing attribute data.


1    Electromagnetic radiation (EMR)
@keyword{Electromagnetic radiation EMR}

 Energy propagated through space or through material media in the form
 of an advancing interaction between electric and magnetic fields. The
 term radiation, alone, is commonly used for this type of energy, although
 it actually has a broader meaning. Also called electromagnetic energy.


1    Electromagnetic Spectrum
@keyword{Electromagnetic Spectrum}

 The ordered array of known electromagnetic radiations, extending from
 the shortest cosmic rays, gamma rays, and x-rays, through ultraviolet
 radiation, visible radiation.


1    Electrostatic printer
@keyword{Electrostatic printer}

 A device for printing graphic images by placing small electrical charges
 on the paper so that a dark or coloured powder, or toner, will adhere in
 these spots.

1    Element
@keyword{Element}

 The smallest definable object of interest in the
 survey. It is a single item in a collection, population, or
 sample.

 See Also: {|}Pixel

1    Elevation
@keyword{Elevation}

 (1) Vertical distance from the datum, usually mean sea
 level, to a point or object on the earth's surface. Not to be
 confused with altitude, which refers to points or objects above
 the earth's surface.


1    Ellipsoid (of reference)
@keyword{Ellipsoid}

 The shape of the planet Earth as expressed as a ratio
 of ellipticity (ellipticity = radius at equator/radius at the poles).


1    Emulate
@keyword{Emulate}

 To imitate another device or program.


1    End lap
@keyword{End lap}

 The overlap of aerial or space photographs or images along the
 flightline or track of the platform.


1    Endmember
@keyword{Endmember}

 One of a number of surface features which when mixed together in varying
 proportions can account for all observed reflectance spectra. For example,
 consider a simple scene that is composed of just water, soil and rock.
 Any given pixel within a digitral image of this scene would be composed of
 varying amounts of water, soil and rock. These three surface features - water,
 soil and rock - would be the endmembers for this particular scene.


1    Ephemeral data
@keyword{Ephemeral data}

 Data that: (1) help to characterize the
 conditions under which data were collected;
 (2) may be used to calibrate the sensor data prior to analysis;
 (3) include such information as the positioning and spectral
 stability of sensors, Sun angle, platform attitude, etc. (sometimes
 called ancillary data).


1    Equal area projection
@keyword{Equal area projection}

 A type of map projection in which areas of the globe
exhibit their correct area but are grossly distorted in shape.

1    Equirectangular projection
@keyword{Equirectangular projection}

 A projection in which the network of meridians and parallels
 intersect at right angles producing a graticule of rectangles.

1    Equivalence
@keyword{Equivalence}

 The ability of a projection to represent areas of any size in
 correct proportion to each other.


1    Error message
@keyword{Error message}

 A code or diagnostic message displayed when the computer
 detects a mistake or inconsistency while a program is being compiled,
 interpreted, or executed.


1    Escape sequence
@keyword{Escape sequence}

 A special kind of command interpreted by a terminal or console device
 and used to control the keyboard and screen. Such commands area called
 `escape sequences' because they begin with the escape (ESC) control byte.


1    Exclusive or
@keyword{OR}

 See also: {|}xor, {|}Boolean operator


1    Expert system
@keyword{Expert system}

 A program that solves a problem posed by a user to that interactively
 assists a user in solving a problem, by using a knowledge base to
 draw inferences. The term derives from the assumption that such systems
 emulate the problem-solving behaviour of a human expert in the field.

 EASI/PACES's procedural language known as EASI+ cab be coupled with the
 MODEL program to create a myriad of complex expert systems.


1    Export
@keyword{Export}

 To produce a file in a form other than the one used internally by the
 program or software product. Software products often provide an export
 capability to help the user create data for competing or complementary
 software products.

 Refer to the help on the GDB for a list of formats in which EASI/PACE can
 currently export information.


1    Expression
@keyword{Expression}

 A mathematical function constructed by combining terms, operators, and
 functions according to the syntax rules of a programming language. For
 example, if x, y, and z area numeric variables, then the following
 are numeric expressions:

 (x + 2) * y
 1 / sqrt(x^2 + y^2)
 ((x > y/2) and (y > 0)) or (z = 0)


1    Extension
@keyword{Extension}

 See Also: {|}file name extension


1    False colour
@keyword{False colour}

 The use of one colour to represent another; for
 example, the use of red emulsion to represent infrared light in
 colour infrared film.


1    Feature
@keyword{Feature}

 An n-tuple or vector with components which are
 functions of the initial measurement pattern variables or some
 sub-sequences of the measurement n-tuples. Feature n-tuples or
 vectors frequently have fewer components than the initial
 measurement vectors and are designed to contain a high amount of
 information about the discrimination between units of the types
 of categories in the given category set. Features often contain
 information about grey shade, texture, shape or context.


1    Feature extraction
@keyword{Feature extraction}

 The process in which an initial measurement
 pattern or some sub-sequence of measurement patterns is
 transformed into a new pattern feature.


1    Fiducial marks
@keyword{Fiducial marks}

 Index marks (usually four), rigidly connected with the camera
 lens through the camera body, which form images on the negative. The
 intersection of lines drawn between opposite fiducial marks defines the
 principal point of the photograph.


1    Field of view
@keyword{Field of view}

 The solid angle through which an instrument is sensitive to radiation.
 Owing to various effects, diffractions, etc., the edges are not sharp.
 In practice they are defined as the \`half-power\' points, i.e., the angle
 outwards from the optical axis, at which the energy sensed by the radiometer
 drops to half its on-axis value.


1    File
@keyword{File}

 A collection of related information in a computer that can be accessed by
 a unique name. Files may be stored on tapes or disks.


1    File name
@keyword{File name}

 (1) The name by which a file is known to an operating system. This
 name must conform to the rules for file naming in the particular operating
 system. (2) The name by which a file is referred to by a program. this name
 must conform tot he rules for naming data items in the particular programming
 language.


1    File name extension
@keyword{File name extension}

 A three-character suffix at the end of a file name in MS-DOS, VAX/VMS,
 and some other operating systems, usually used to identify the type of
 information in the file.

 EASI/PACE has adopted the .pix extension for its PCIDSK database files.


1    Filtering
@keyword{Filtering}

 In digital image processing, a transformation process used to assign
 new values to each pixel of a reaster image, based on the values of
 neighbouring pixels contained in a window of specified size.


1    Flight line
@keyword{Flight line}

 A line drawn on a map or chart to represent the
 tracking over which an aircraft has been flown or is to fly.


1    Floating point
@keyword{Floating point}

 A data type for representing very large and small numbers, in
 which part of a data unit is reserved for an exponent, and part for
 representing a mantissa.

 EASI/PACE's 32R channel types support floating point data.


1    Floppy disk
@keyword{Floppy disk}

 A circular, flexible, relatively inexpensive piece of magnetic
 material for the storage of digital data.


1    Flow chart
@keyword{Flow chart}

 A graphic representation of an algorithm, with well-defined steps
 linked by flow lines to indicate the sequence of operations.


1    Flush
@keyword{Flush}

 To empty buffers or queues intentionally, usually as part of file closing,
 program termination, or system shutdown.


1    Focal length
@keyword{Focal length}

 The distance measured along the optical axis from the optical
 centre (near nodal point) of the lens to the plane of critical focus of a very
 distant object.


1    Font
@keyword{Font}

 An assortment of letters, numbers, and special characters of the same
 typeface.


1    Format
@keyword{Format}

 The way in which data are systematically arranged for transmission
 between computers, or between a computer and a device. Standard format
 systems are used for many purposes.


1    Fourier analysis
@keyword{Fourier analysis}

 A method of dissociating time series or spatial data into sets
of sine and cosine waves. (PGIS)
Freeware: Software that is available to the public, but of which the author
retains ownership.


1    Gaussian
@keyword{Gaussian}

 A statistical term that refers to a Normal distribution of values.
 A distribution of data that can be well characterized by its two moments
 (mean and variance) is said to be "normally" distributed.


1    GCP
@keyword{GCP}

 Ground control point. A geographical feature of known
 location that is recognizable on images and can be used to
 determine geometrical corrections.


1    Geocoding
@keyword{Geocoding}

 The activity of defining the position of geographical objects in
 relation to a standard reference grid


1    Geoid
@keyword{Geoid}

 An Earth shaped body considered either as a mean seal-level surface
 extended continuously through the continents or as an undulating surface
 lower than the surface of the spheroid beneath the oceans and higher beneath
 continents.


1    Geometrical transformations
@keyword{Geometrical transformations}

 Adjustments made in the image data
 to change its geometrical character, usually to improve its
 geometrical consistency or cartographic utility.


1    Gigabyte
@keyword{Gigabyte}

 Literally, one billion (109) bytes, in american English usage.
 Contrary to ordinary English usage, in programming a kilobyte has come to
 mean 1,024 (212) bytes when referring to random access memory (RAM),
 mass storage space (such a shared disks), or storage media measured in powers
 of two. Similarly, one gigabyte (1,024M) is 1,073,741,824 (230 bytes).


1    GIGO
@keyword{GIGO}

 An acronym - garbage in, garbage out - for a common-sense phrase
 conveying the value of accurate input to a data processing system.


1    GIS

 @keyword{GIS}

 Geographical Information System: a set of software and hardware for
 collecting and analyzing spatial information for particular applications.


1    Gnomic projection
@keyword{Gnomic projection}

 A azimuthal projection from the centre of the generating globe on the
 tangent plane. All arcs of the great circle are represented by straight lines.


1    Graphical user interface
@keyword{Graphical user interface}

 See Also: {|}GUI

1    Graphic plane
@keyword{Graphic plane}

 A memory on video displays that is one bit deep.
 Graphic planes act as non-destructive masks overlaying any data
 underneath them.

 See also: {|}Bitmap


1    Graticule
@keyword{Graticule}

 The network of parallels of latitude and meridians of longitude as
 plotted on a map projection.


1    Great circle
@keyword{Great circle}

 The line of intersection of the surface of a sphere with a plane
 passing through the centre of the sphere. A great circle is the
 largest circle that can be drawn on a sphere.


1    Grey scale
@keyword{Grey scale}

 A calibrated sequence of grey tones ranging from black to white.


1    Ground control
@keyword{Ground control}

 Accurate data on the horizontal and/or vertical
 positions of identifiable ground points.


1    Ground data
@keyword{Ground data}

 Supporting data collected on the ground, and
 information derived therefrom, as an aid to the interpretation
 of imagery, such as airborne imagery, etc.
 Generally, this should be performed concurrently with the
 collection of imagery. Data as to weather, soils and vegetation types
 and conditions are typical.


1    Ground information
@keyword{Ground information}

 Information derived from ground data and
 surveys to support interpretation of image data.


1    Ground range
@keyword{Ground range}

 The distance from the ground track (nadir) to a
 given object.


1    Ground resolution cell
@keyword{Ground resolution cell}

 The area on the terrain that is covered
 by the instantaneous field of view of a detector. The size of
 the ground resolution cell is determined by the altitude of the
 remote-sensing system and the instantaneous field of view of the
 detector.


1    Ground truth
@keyword{Ground truth}

 Term coined for data and information obtained on surface or
 subsurface features to aid in interpretation of remotely sensed data.
 (jargon)

 See also: {|}Ground data, {|}Ground information


1    GUI
@keyword{GUI}

 An approach to communication between online users and software,
 characterized by the following:
 (1) The use of pictorial icons to represent such objects as files, programs,
 peripheral devices, windows, menus and data.
 (2) The use of a pointing device, such as a mouse, with which the user can
 select objects, initiate a process and move an object.
 (3) A view of the screen as if it were a desktop, a control panel, or both.

 EASI/PACE offers a number of GUI's to simplify its use. The most common
 ones include: Xpace, pciworks, ImageWorks, and GCPWorks.

 See Also: ImageWorks, GCPWorks, PCIWorks


1    Halftone image
@keyword{Halftone image}

 A photograph or other image having continuous shades of grey, from
 lightest to darkest. Halftone images are crated through a crossline
 or contact screen that converts the image to dots of varying sizes. Although
 halftone images have played little role in traditional data processing, they
 are increasingly being used in desktop publishing and other applications that
 generate graphic output.


1    Hard copy
@keyword{Hard copy}

 A permanent image of a map or diagram or permanent report of text.
 For example, a paper map produced on a line printer or a paper report of
 text.


1    Hashing
@keyword{Hashing}

 A method of encoding data, used by indexing algorithms, to determine the
 relationship of individual data elements. A hashing algorithm is used to
 determine a hash index, which is an initial estimate of where a data item
 will fit within an index table.

 EASI/PACE's programs NGCLUS and NGCLUS2 makes use of hash tables.


1    Header
@keyword{Header}

 That portion of a file which preceeds the actual data and may contain
 such information as sensor characteristics, time, date and location of data
 acquitistion, structure of the data, generating agency, etc.


1    Help
@keyword{Help}

 Online instructions to assist users in using a program. These instructions
 come in a variety of forms, including screens of information that users can
 scroll, menus that provide the user with help options, or small popup windows.

 EASI/PACE's XPACE allows you to invoke help through button and
 pulldown menu selections while EASI+ lets you invoke help by typing help
 followed by the name of the program for which help is desired.


1    Hertz (Hz)
@keyword{Hertz}

 A measure of frequency for a periodic event, in cycles per second.
 The term is usually used with standard prefixes, as in megahertz (MHz).


1    Histogram
@keyword{Histogram}

 The graphical display of a set of data which shows the
 frequency of occurrence of individual measurements or values; a
 frequency distribution.


1    Hotelling transform
@keyword{Hotelling transform}

 See also: {|}Principal components


1    Hot key
@keyword{Hot key}

 A key or set of keys that invokes a program when pressed. Hot keys
 are usually associated with a terminate-and-stay-resident (TSR) program that
 is activated any time the user presses a particular key combination.


1    Hotspot (sunspot)
@keyword{Hotspot sunspot}

 The destruction of fine image detail on a portion of an aerial photograph.
 It is caused by the absence off shadows and by halation near
 the prolongation of a line from the sun through the exposure station.


1    Hue
@keyword{Hue}

 That attribute of a colour by virtue of which it differs
 from grey of the same brilliance, and which allows it to be
 classed as red, yellow, green, blue, or intermediate shades of
 these colours.


1    Hyperspectral
@keyword{Hyperspectral}

 Very high spectral resolution imagery. Data are acquired in
 224 contiguous channels of approximately 10nm bandwidth, spanning the
 0.4-2.5 um region of the electromagnetic spectrum AVIRIS is the most widely
 used form of hyperspectral data.


1    Icon
@keyword{Icon}

 A small, pictorial representation of an object such as a program, file, or a
 device. Graphical user interface (GUI) systems display icons on the user's
 screen to represent objects.


1    Illumination
@keyword{Illumination}

 The intensity of light striking a unit surface is known as illumination.
 It varies directly with the intensity of the light source and inversely as
 the square of the distance between the illuminated surface and the source.


1    Image
@keyword{Image}

 The recorded representation of an object produced by
 optical, electro-optical, optical mechanical, or electronic means.


1    Image analysis
@keyword{Image analysis}

 Encompasses all the various operations that can be applied to photographic
 or image data. These include, but are not limited to, image compression
 image restoration, image enhancement, preprocessing, quantization,
 spatial filtering, and other image pattern recognition techniques.


1    Image enhancement
@keyword{Image enhancement}

 Any one of a group of operations that improve
 the visual or electronic detectability of the targets or categories.
 These operations include, but are not limited to, contrast
 improvement, edge enhancement, spatial filtering, noise suppression,
 image smoothing, and image sharpening.


1    Image plane
@keyword{Image plane}

 (1) A memory for digital image data on a video
 display, usually 8 bits per pixel. (2) A place of storage for digital
 image data on a PCIDSK file (usually called a "channel").


1    Image processing
@keyword{Image processing}

 Encompasses various image operations, including but
 are not limited to image compression, image restoration, image
 enhancement, preprocessing, quantization and spatial filtering.


1    Image restoration
@keyword{Image restoration}

 A process by which a degraded image is restored to its original condition.
 Image restoration is possible only to the extent that the degradation
 transform is mathematically invertible.


1    Imagery
@keyword{Imagery}

 The products of image-forming instruments.


1    Import
@keyword{Import}

 To read a file that was created by some other program in a form different
 from the format and structure normally used in the importing program.

 Refer to the help on the GDB for a list of formats in which EASI/PACE can
 currently import information.


1    Infrared
@keyword{Infrared}

 The portion of the electromagnetic spectrum bounded by visible light and
 by microwave radiation. Infrared wavelengths just longer than those of
 visible light are called near infrared, whereas the longer infrared
 wavelengths, sensible as heat, are called thermal infrared.


1    Initialize
@keyword{Initialize}

 To set to an initial value or state.

 An EASI/PACE example if initialization is offered in the pseudo-colour
 editing panel of ImageWorks; here four initial pseudo-colour states are
 provided for application to the image being viewed in video.


1    Ink-jet printer
@keyword{Ink-jet printer}

 A display device that prints characters and greytones as patterns of small
 dots formed by tiny drops of ink sprayed onto the plotting medium.


1    Instantaneous field of view (IFOV)
@keyword{Instantaneous field of view IFOV}

 A term specifically denoting the narrow field of view designed into
 detectors, particularly scanning radiometer systems, so that, while
 as much as 120 degrees may be under scan, only electromagnetic radiation
 from a small area is being recorded at any one instant.


1    Integer
@keyword{Integer}

 A whole number, either positive or negative. As implemented in
 programming languages, integers are usually defined as numbers within a
 certain range. This range is defined by the number of bytes allocated in
 memory to represent the integers.

 EASI/PACE allows you to store your image data in any one of three types of
 integer data types:
 (1) 8U enabling storage of values between 0 and 255
 (2) 16S enabling storage of values between -32,767 and +32,768
 (3) 16U enabling storage of values between 0 and 65,553


1    Intensity
@keyword{Intensity}
 Intensity refers to a SAR (Synthetic Aperture Radar) data format.  The
 terms Power and Intensity are synonymous and are teh equivalent of
 amplitude (data) squared.  See also POWER and Amplitude.


1    Interactive image processing
@keyword{Interactive image processing}

 The activity of an operator or
 analyst at a console assessing, preprocessing, feature extracting,
 classifying, identifying, and displaying the original imagery or the
 processed imagery for subjective evaluations and further interactions.


1    Interface
@keyword{Interface}

 A set of conventions and procedures that define the communication
 between the following:
  - A program and the user; for example, the screen the user sees and
    interacts with to control the actions of the program.
  - One program and another; for example, the set of functions an application
    program can call to control a graphical user interface (GUI).
  - Software and hardware; for example, a device driver that handles
    interaction with a printer or a disk drive.

 See also: {|}GUI


1    Internal memory
@keyword{Internal memory}

 That integral part of a computer immediately accessible by the CPU for the
 storage and retrieval of data, also called main memory or core storage.


1    Interpolate
@keyword{Interpolate}

 To estimate the value of an attribute at an unsampled point from
 measurements made at surrounding sites.


1    Intersection
@keyword{Intersection

 The set containing all objects common to two intersecting sets.
 Formally, x is an element of the intersection set of sets A and B, if,
 and only if, x is an element of A and x is an element of B.

 See also: {|}union


1    Isocentre
@keyword{Isocentre}

 The isocentre is the point on the photo that falls on a line and
 halfway between the principal point and the nadir. On a true vertical aerial
 photograph the principal point, isocentre, and the nadir all coincide at the
 geometric centre of the photograph as defined by the intersection of lines
 drawn between opposite fiducial marks. The isocentre is the point from which
 tilt displacement radiates.


1    Iteration
@keyword{Iteration}

 Repeated execution of a sequence of instructions. In addition, it
 connotes the computing of successively closer approximations to a problem
 solution, such as occurs when summing the terms of a convergent series.


1    Kappa coefficient
@keyword{Kappa coefficient}

 An index value ranging between 0 and 1 which expresses the proportionate
 reduction in error achieved by a classifier as compared with the error of
 a completely random classifier. Thus, a value of 0.75 would indicate that
 the classifier was avoiding 75 percent of the errors that a totally
 random process would have produced.


1    Key
@keyword{Key}

 A 27-character, alphanumeric digital code used by PCI to identify which
 software packages a user has permission to access.


1    Keyboard
@keyword{Keyboard}

 The initial and primary input device for almost all computing
 equipment. There are many variations of terminal and microcomputer
 keyboards, but all have at least the standard typewriter characters. Computer
 keyboards add special function keys, cursor-movement keys, and terminal
 control keys. Virtually all keyboards used for programming or general
 applications have the standard `qwerty' arrangement for letters, numbers, and
 most special characters, but the placement of function, cursor-movement, and
 terminal control keys varies considerably.


1    Keyword
@keyword{Keyword locate}

 In EASI/PACE a search utility which helps locate all programs and
 definitions related to a user-supplied term. In EASI, type `help keywords'
 for more details.


1    Kilobyte
@keyword{Kilobyte}


 Literally, one thousand bytes, usually abbreviated as K. Contrary to
 generally accepted usage, in programming a kilobyte has come to mean 1.024
 bytes when referencing random-access memory (RAM) or mass storage space
 (such as hard disks). Thus a 640K machine actually has 655,360 bytes.
 The ambiguity resulting from the use of the same prefix to represent
 both 1,000 and 1,024, while regrettable, is seldom serious, as the
 difference is relatively small.

 See also: {|}gigabyte, {|}megabyte

1    Kurtosis
@keyword{Kurtosis}

 The fourth moment about the mean which is a measure of peakedness.


1    Lambert equal area projection
@keyword{Lambert equal area projection}

 A projection where the scale along the equator is correct but decreases
 on the meridians polewards, causing parallels to become closer together
 as they approach the poles.


1    Laser printer
@keyword{Laser printer}

 An output device that uses a laser to paint dots of light onto an
 electrophotographic drum or belt. After the laser transfers the image to the
 drum, toner is applied to the drum or belt, then paper moves through the
 printer, similar to a copier.

 Laser printers usually are more expensive than, but preferable to, dot-matrix
 and daisy-wheel printers. Laser printers can print more pages per minute, at
 resolution of 300 to 600 DPI (dots-per-inch). Printouts typically are crisp and
 clean, and visually superior to those generated with other printing methods.


1    Latitude
@keyword{Latitude}

 The angular distance north or south of the equator, measured along
 a meridian and expressed either in decimal degrees or in degrees,
 minutes and seconds.


1    Least-squares
@keyword{Least-squares}

 A method of estimation for which the best result is that yielding the
 minimum value for the sum of the squared deviations between the
 actual and predicted values.


1    Legend
@keyword{Legend}


 The part of the drawn map explaining the meaning of the symbols
 used to code the depicted geographical elements.


1    Line
@keyword{Line}

 One of the basic geographical elements, defined by at least two paris of
 x,y coordinates.


1    Lineament
@keyword{Lineament}

 A linear topographical or tonal feature on the
 terrain and on images and maps, which may represent a zone of
 structural weakness.


1    Linear feature
@keyword{Linear feature}

 A two-dimensional, straight or curved line, linear pattern, or alignment
 of discontinuous patterns evident in an image, photo, or map, which
 represents the expression of some degree of linearity of a single or diverse
 grouping of natural or cultural ground features.


1    Line printer
@keyword{Line printer}

 An output device, usually connected to a mainframe or minicomputer,
 that prints one line at a time, commonly on 11-inch by 17-inch
 `greenbar' paper. Line printers are very fast and often provide excellent
 print quality, but they lack the capability of laser printers to print
 graphics images and different fonts.


1    List box
@keyword{List box}

 In graphical user interface (GUI), a small window that presents to the
 user a list of mutually exclusive alternatives, such as a list of fonts.
 When such a list is too long to fit in the window, the user can scroll it
 by using a scroll bar or the cursor keys.

 When loading image channels to video, ImageWorks provides the user with a
 list box of channels resident on the currently active/selected database file.


1    Log file
@keyword{Log file}

 A file containing a record of computer activity.


1    Logical operation
@keyword{Logical operation}

 An operation involving program variables that is either true or false.
 Three examples of logical operations are `A equal to B', `C
 greater than D', and `A equal to B AND C greater than D.'


1    Longitude
@keyword{Longitude}

 The angular distance east or west of the prime meridian at Greenwich,
 England, to the point on the earth's surface for which the longitude
 is being determined, expressed either in decimal degrees or degrees,
 minutes and seconds.


1    Look angle (radar)
@keyword{Look angle (radar)}

 The direction of the look, or direction in
 which the antenna is pointing when transmitting and receiving.


1    Look direction
@keyword{Look direction}

 Direction in which pulses of microwave energy
 are transmitted. Look direction is normal to
 the azimuth direction. Also called range direction.


1    Lowercase
@keyword{Lowercase}

 The small, noncapitalized alphabetic letters a through z.


1    Magnetic tape
@keyword{Magnetic tape}

 A long, thin, magnetically coated storage medium, usually wound on a reel.


1    Map
@keyword{Map}

 A representation in a plane surface, at an established
 scale, of the features (natural, inferred or cultural)
 of a part of the Earth's surface, with the means of orientation
 indicated.


1    Map, large-scale
@keyword{Map, large-scale}

 A map having a scale of 1:100,000 or larger.


1    Map, medium-scale
@keyword{Map, medium-scale}

 A map having a scale from 1:100,000
 to 1:1,000,000.


1    Map, small-scale
@keyword{Map, small-scale}

 A map having a scale smaller than 1:100,000.


1    Map, thematic
@keyword{Map, thematic}

 A map designed to demonstrate particular features
 or concepts. In conventional use this term excludes
 topographical maps.


1    Mask
@keyword{Mask}

 A bitmap, or rectangular window used to define the area within an
 image channel for which processing will take place.


1    Maximum likelihood rule
@keyword{Maximum likelihood rule}

 A statistical decision criterion to
 assist in the classification of overlapping signatures; pixels
 are assigned to the class of highest probability.


1    Mean
@keyword{Mean}

 The arithmetic mean is given by the sum of an array of numbers divided
 by the total number of observations in that array.


1    Median
@keyword{Median}

 The median divides a set of ranked observations into two groups of
 equal size. If one has (N/2) + (1/2).


1    Megabyte
@keyword{Megabyte}

 Literally, one million (106) bytes, usually abbreviated as M.
 Contrary to generally accepted usage, in programming a kilobyte has come to
 mean 1,024 bytes when referencing random access memory (RAM) or mass
 storage space (such as hard disks). Thus 1M (1,024 kilobytes) is 1,048,576
 (220) bytes. The ambiguity resulting from the use of the same prefix to
 represent both 1,000,000 and 1,048,576 although regrettable, is seldom
 serious, because the difference is relatively small. (CPD)

 See also: {|}gigabyte, {|}kilobyte


1    Memory
@keyword{Memory}

 Any medium that can store and retrieve data, most often specifically the
 high-speed internal random access (RAM) storage used for instructions and data.

 RAM is volatile; when the computer is shut off or restarted, the contents of
 memory are lost. You must save to disk any information loaded into memory
 before shutting off the computer's power, or the information will be lost.

 After programs are loaded from disk into RAM, they are executed in the
 computer's memory. When data moves into memory, it replaces the previous
 contents of that portion of memory.

 Memory also can be read-only memory (ROM), in which data is preloaded and
 cannot be changed as with RAM. ROM contains the PC's lowest operating
 system, the BIOS (Basic Input Output System). ROM `remembers' its data
 after the power is turned off.

 All types of memory are accessed by address. Each address is simply as
 electronic representation of a unique number which, in turn, can represent
 text, characters, numbers, images, or instructions for the computer.


1    Memory-resident program
@keyword{Memory-resident program}

 A program that remains in memory even when it is not executing. Programs
 that respond to frequently occurring events are appropriately made
 memory-resident. They include many modules of the operating system's
 kernel, most device drivers, and hot key handlers.

 See also: {|}TSR


1    Menu Mode
@keyword{Menu}

 A list of options on a display allowing an operator to select the next
 operations by indicating one or more choices with keystroke or mouse button
 selection.

 EASI/PACE offers a menu interaction via the SHELL interface. Xpace is a
 more sophisticated GUI menu interface.

 See also: {|}list box, {|}pulldown menu


1    Mercator projection
@keyword{Mercator projection}

 A map projection centred along the Equator with evenly spaced meridians
 perpendicular to parallels spaced progressively farther apart poleward
 so that compass bearings are not distorted.


1    Mercator projection, transverse
@keyword{Mercator projection transverse}

 Uses the same system of projection as the Mercator Projection, but with
 the projection centred along a meridian to provide low distortion with
 a zone around the central meridian.

1    Merge
@keyword{Merge}

 To combine two or more sorted files, arrays, or lists, into a single
 sorted file, array or list. The inputs all have the same structure,
 and are in sequence by the same key field.

 EASI/PACE programs SIGMERG and VECMERG allow the merging of
 and vectors, respectively.

 See Also: SIGMERG, VECMERG

1    Minimum distance classifier
@keyword{Minimum distance classifier}

 A classification technique that assigns raw data to the class whose mean
 falls the shortest Euclidean distance from it.


1    MIPS (Million Instructions Per Second)
@keyword{MIPS}

 The commonly used unit of measure for the internal speed of a computer.
 Computers are rated using this standard, although the measurement alone
 may not be sufficient to provide an accurate comparison of the performance
 of widely different types of computers. High-performance personal computers
 can operate between 20 to 50 MIPS, and this speed is increasing with each
 new development in the technology.


1    Mode
@keyword{Mode Bimodal}

 The most frequently occurring value (or class) in an array of numbers.
 When there is a single dominant frequency, the distribution is unimodal.
 When there are two equally dominant frequencies, the distribution is bimodal.
 In cases where several modes or modal classes occur, then one might be
 inclined to describe such a distribution as multimodal.


1    Modem
@keyword{Modem}

 A device that converts a digital signal to analog for transmission
 (usually over the public switched network), then back to digital forma
 after reception. A modem is required at each end of the link. the term
 is a contraction of modulator/demodulator.


1    Monochromatic
@keyword{Monochromatic}

 Pertaining to a single wavelength or, more commonly, to a narrow band
 of wavelengths.


1    Mosaic
@keyword{Mosaic}

 An assemblage of overlapping images whose edges have been matched to
 form continuous pictorial representation of a portion of the Earth's surface.


1    Mosaic, controlled
@keyword{Mosaic, controlled}

 A mosaic that is laid to ground control and uses prints that have been
 rectified as shown to be necessary by the control.


1    Mosaicking
@keyword{Mosaicking}

 The assembling of images whose edges are cut and matched to form a continuous
 representation of a portion of the Earth's surface.


1    Motif
@keyword{Motif}

 A graphical user interface (GUI) created by the Open software
 Foundation (OSF) to operate with the X window interface. Motif, which
 consists of a development library and an interface manager, provides support
 for enhanced graphical user interface (GUI) applications.

 PCI's product line has adopted the Motif standard for its GUIs.


1    Mouse
@keyword{Mouse}

 A computer input device used for pointing and drawing with computer
 programs. When the device is moved on a flat surface, a cursor or pointer
 makes corresponding moves across the screen.

 You can use a mouse to select a block of text, draw a line, select a menu
 option, and so forth. Some graphics-oriented programs require a mouse for
 easy operation. A mouse connected to the serial port of a computer is called
 a serial mouse. A mouse connected by a special PC card is called a bus mouse.

 See also: {|}click, {|}double-click, {|}drag and drop, {|}GUI

1    Mouse button
@keyword{Mouse button}

 On a mouse, the key or switch that enables you to control software.
 Pressing a mouse button results in a mouse click.

1    MSS
@keyword{MSS}

 See also: {|}Multispectral (line) Scanner

1    Multiband system
@keyword{Multiband system}

 A system for simultaneously observing the same (small) target with several
 filtered bands, through which data can be recorded. Usually applied to
 scanning radiometers that use dispersant optics to split wavelength bands
 apart for viewing by several filtered detectors.


1    Multichannel system
@keyword{Multichannel system}

 Usually used for scanning systems capable of observing and recording several
 channels of data simultaneously, preferably through the same aperture.


1    Multispectral
@keyword{Multispectral}

 Generally used for images in two or more spectral bands, such as visible and IR.


1    Multispectral (line) scanner
@keyword{Multispectral (line) scanner}

 A remote sensing device that
 operates on the same principle as the infrared scanner, except
 that it is capable of recording data in the ultraviolet and
 visible portions of the spectrum as well as the infrared.


1    Multitasking
@keyword{Multitasking}

 The capability of an operating system to run two or more
 programs in the same computer at the same time. operating systems that
 provide multitasking to personal computers include UNIX, Microsoft
 Windows, and OS/2. In a multitasking operating system, the user can move
 from application to application while the applications continue processing.
 Generally, multitasking operating systems require larger portions of memory
 and processing poser than single0tasking operating systems such as Ms-DOS.


1    Multivariate analysis
@keyword{Multivariate analysis}

 A data-analysis approach that makes use
 of multidimensional interrelations and correlations within the
 data for effective discrimination.


1    Nadir
@keyword{Nadir}

 (1) That point on the celestial sphere vertically below
 the observer, or 180 degrees from the zenith. (2) That point on
 the ground vertically beneath the perspective center of the
 camera lens.


1    Nautical mile (abbr. knot)
@keyword{Nautical mile (abbr. knot)}

 A unit of distance used principally in navigation. It is usually considered
 the length of one minute of any great circle of the Earth, the meridian
 being the great circle most commonly used.  Also called sea mile.


1    Neural network
@keyword{Neural network classify classification}

 An artificial intelligence modelling technique which attempts to mimic the
 computational abilities of the brain.

 In EASI/PACE, nearual network algorithms have been adopted to
 classification techniques. Refer to programs MAL, AVG, NNCLASS,
 NNCREAT and NNTRAIN for further information.


1    nm
@keyword{nm nanometre nanometer}

 An abbreviation for the unit of measure known as the nanometre. 1 nanometre
 equals 0.000000001 metres.


1    Normal distribution
@keyword{Normal}

 See Gaussian.


1    Normalization
@keyword{Normalization}

 Adjustment of a set of data values to a common unit of
 measure for comparison purposes with another data set.


1    Not
@keyword{Not logical}

 A unary logical operator that negates the value of the variable it operates
 on: if A is TRUE, not A is FALSE. The not operator is often used to construct
 logical expressions for controlling program execution or for developing
 database selection criteria.

 See also: {|}and, {|}or, {|}xor


1    NT (New Technology)
@keyword{NT New Technology}

 See also: {|}Windows NT

1    Null string
@keyword{Null string}

 In languages that support character string operations, a zero-length
 or empty string.


1    Offline
@keyword{Offline}

 The transmission of information between a computer and peripheral
 unit before, or after, but not during, processing, in contrast to online
 processing.


1    Online
@keyword{Online}

 The transmission of information between a computer and a terminal or display
 device while processing is occurring, in contrast to offline processing.


1    Operating system
@keyword{Operating system}

 A set of software and standards for managing the hardware resources in
 a computer system and for providing standard interfaces between other
 programs (jobs) and both the hardware and human users. In addition to the
 services provided by the operating system kernel, a typical operating system
 for a multiple-user configuration does the following:

 (1) Controls access by users to the system;
 (2) Enforces security and privacy of files;
 (3) Schedules batch jobs;
 (4) Allocates resources to jobs, including memory, disk space, and devices;
 (5) Controls peripheral SPOOL functions, especially printing.


1    Or
@keyword{Or logical}

 A binary logical operator that is assigned the value TRUE only if either or
 both of its operands are true.


1    Orbit
@keyword{Orbit}

 (1) The path of a body or particle under the influence of a gravitational or
 other force. For instance, the orbit of a celestial body is its path relative
 to another body around which it revolves. (2) To go around the Earth or other
 body in an orbit.


1    Order of operations
@keyword{Order of operations}

 The language-defined sequence in which arithmetic and logical operations
 are performed in complex expressions; also called operator precedence.
 Almost all languages follow the traditional order of evaluation
 familiar in algebra: Quantities in parentheses are evaluated first, then
 exponentiation, then multiplication and division, and finally addition and
 subtraction.


1    Orthogonal
@keyword{Orthogonal}

 See also: {|}perpendicular


1    Orthophotograph
@keyword{Orthophotograph}

 A photograph having the properties of an orthographic projection. It is
 derived from a conventional perspective photograph by simple or differential
 rectification so that image displacements caused by camera tilt and terrain
 relief are removed.


1    OS/2
@keyword{OS/2}

 An operating system for the Intel (IBM-compatible) series of desktop
 computers (80386 and above). OS/2 features a graphical user interface (GUI),
 multithreading, dynamic data exchange (DDE), and a diverse repertoire of
 integrated services including LAN operation, communications, and a
 relational database manager.

 OS/2 was originally planned jointly by IBM and Microsoft as a proposed
 standard for the 32-bit processor architecture. It was expected to provide
 much greater power and flexibility than MS-DOS, as well as easier and more
 efficient operation than Windows. When Microsoft later elected to pursue an
 independent direction (see Windows NT), OS/2 became known as IBM's entry
 in a hotly contested operating system market.


1    OSF
@keyword{OSF}

 The Open Software Foundation, a nonprofit organization formed to
 promote nonproprietary computing environments, especially on UNIX or
 operating systems.The organization's members include several
 computer companies. OSF has created such software standards as the OSF
 Motif graphical user interface (GUI) and development system, and OS/1, an
 operating system based on INUX. Additionally, OSF solicits innovations from
 the industry, and publishes agreed-on technical standards for its members.

 See also: {|}Motif


1    Overflow
@keyword{Overflow}

 (1) An exception that occurs when a result of a computation is larger
 than the register available for it. (2) Any attempt to exceed some fixed storage
 capacity, such as the capacity of a table, a stack, a disk, or a file.


1    Overlay
@keyword{Overlay}

 See also: {|}Graphic plane

1    PACE
@keyword{PACE}

 Picture Analysis, Correction and Enhancement; PCI's image
 processing and analysis software.


1    Paged memory
@keyword{Paged memory}

 A portion of total system memory divided into pages, then
 moved to and from disk as required by the program. Paged memory is brought
 into memory as memory becomes available, depending on the execution
 scheme of the program. Pages not brought into memory are kept on disk until
 are necessary.

 See also: {|}virtual memory


1    Panchromatic
@keyword{Panchromatic}

 A term used to describe films that are sensitive to the ultraviolet and
 entire visible portion of the electromagnetic spectrum.
 Panchromatic film (black-and-white photographs) has long been the
 `standard' film type for aerial photography.


1    Parallax
@keyword{Parallax}

 The apparent change in the position of one object, or point, with
 respect to another, when viewed from different angles. As applied to aerial
 photos, the term refers to the apparent displacement of two points along the
 same vertical line when viewed from a point (the exposure station) not on the
 same vertical line.


1    Parallax, absolute
@keyword{Parallax absolute}

 In a pair of truly vertical photographs which have equal flight heights, or
 in a pair of rectified photographs, the term denotes the algebraic difference,
 parallel to the air base, of the distances of the two images
 form their respective principal points. Also called `x-parallax'.


1    Parallax difference
@keyword{Parallax difference}

 The difference in the distances separating image points for two ground
 points of different elevation, as measured on a stereo pair of photos
 correctly oriented with respect to one another.


1    Parallel port
@keyword{Parallax port}

 An input-output (I/O) connector used to attach a printer (or other
 device) to a computer.

 A PC uses a DB-25 connector to provide this connection. Data is transferred
 through a parallel port in 8-bit wide pieces, enabling a complete character
 to be sent in one move. Serial devices, in contrast, pass only one bit at a
 time, requiring eight moves for one character. Parallel ports also can be
 used to connect portable network adapters to the computer, so that the
 parallel ports can transmit data to a network.
 Intel computers name the parallel ports LPT1, LPT2, and LPt3.


1    Parameter
@keyword{Parameter}

 A parameter is simply a program or system variable which controls the
 operation of a single aspect of a PACE program. As a user, you are
 able to specify parameter values and hence control the operation of any
 particular PACE program.


1    Parameter file
@keyword{Parameter file}

 A place of storage on disk for EASI and PACE control variables.


1    Passive remote sensing
@keyword{Passive remote sensing}

 Remote-sensing systems that are dependent upon natural sources of external
 energy such as solar radiation or thermal infrared emissions
 (e.g. electro-optical sensors).


1    Path
@keyword{Path}

 The disk drive address and list of directory nodes leading from the root
 directory to the directory containing a specific file.

 For example, in the path:

 B:\PCI\DEMO\IRVINE.PIX

 everything up to IRVINE.PIX defines the path from the root directory to that
 file.


1    Pattern
@keyword{Pattern}

 In a photo image, the regularity and characteristic
 placement of tones or textures. Some descriptive adjectives for
 patterns are regular, irregular, random, concentric, radial and rectangular.


1    Pattern recognition
@keyword{Pattern recognition}

 Concerned with, but not limited to, problems of pattern discrimination,
 pattern classification, feature selection, pattern identification, cluster
 identification, feature extraction, etc.

1    Peripheral device
@keyword{Peripheral device}

 A hardware device that may be added to a computer to
 provide additional data storage or to receive or display data.


1    Perpendicular
@keyword{Perpendicular}

 A line, plane, or surface which is at right angles (90 degrees)
 to another line, plane or surface. This \`other\' surface is often a
 horizontal at a given point on the Earth's surface


1    Perspective
@keyword{Perspective}

 Representation, on a plane or curved surface, of natural objects as they
 appear to the eye.


1    Perspective projection


 The projection of points by straight lines through a
 single, given point to their intersections with the plane of projection.


1    Phosphor
@keyword{Phosphor}

 A phosphorescent substance which emits light when
 excited by radiation, as on the scope of a cathode-ray tube.


1    Photogrammetry
@keyword{Photogrammetry}

 The science or art of obtaining reliable measurements by
 means of photographs.


1    Pitch
@keyword{Pitch}

 Rotation of an aircraft about the horizontal axis normal
 to its longitudinal axis, which causes a nose-up nose-down
 attitude.


1    Pixel
@keyword{Pixel}

 (Derived from "picture element") A data element having
 both spatial and spectral aspects. The spatial variables define
 the apparent size and position of the resolution cell (i.e., the area on the
 ground represented by the data values), and the spectral
 variables define the intensity of the spectral response for that
 cell in n channels.


1    PKZIP
@keyword{PKZIP}

 In the MS-DOS environment, a shareware program developed by
 PKware, Inc., which implements dynamic file compression. PKZIP uses a
 Lempel-Ziv algorithm to compress data to the smallest number of bytes. The
 advantage of using such a program is that the smaller file sizes allows for
 quicker data transmission (and subsequent phone charges) and smaller disk-
 storage requirements.


1    Plane coordinates
@keyword{Plane coordinates}

 Coordinates specifying the locations of points in a plane.
 In cartography the plane usually is a projection of the Earth's surface onto a
 flattenable cone or cylinder, and X and Y values scaled along the rectangular
 axes are called eastings and northings, respectively.


1    Planimeter
@keyword{Planimeter}

 An instrument used to measure the area of any figure by passing
a tracer around its boundaries and recording the area encompassed.


1    Planimetric map
@keyword{Planimetric map}

 A map that represents only the horizontal positions of features. A
 planimetrically accurate map shows accurate horizontal distances
 between features.


1    Polarization
@keyword{Polarization}

 The direction of vibration of the electrical field vector of
 electromagnetic radiation. In SLAR systems polarization is either
 horizontal or vertical.


1    Polygon
@keyword{Polygon}

 A two-dimensional figure with three or more straight-line sides
 intersecting at a like number of points.


1    Polynomial
@keyword{Polynomial}

 A linear combination of the products of integer powers of a set of
 variables, for example, X^2 + 5X + 4XY.


1    Popup window
@keyword{Popup window}

 A small window, usually a menu or dialog box, that is invoked by a program
 and displayed on top of that program's main window, to prompt the user for
 a reply. After the user responds, the popup window disappears.

 Programs often display a popup menu in response to a user-initiated action,
 such as a mouse click or a hot key. This is a common way for users to request
 a function under a graphical user interface (GUI).


1    Portrait orientation
@keyword{Portrait orientation}

 The property of an output (hard copy of display) having its vertical
 dimension longer than its horizontal dimension. Portrait orientation
 is the converse of landscape orientation, in which output is displayed
 with a longer horizontal dimension.


1    Postscript
@keyword{Postscript}

 A proprietary programming language of Adobe systems Inc. The
 language is useful for the following purposes:
 (1) To describe printed pages containing text, geometric figures, and sampled
 images in almost any layout;
 (2) To direct the printing of such pages on a graphic printer.


1    Power
@keyword{Power}

 Power refers to a SAR (Synthetic Aperture Radar) image that has been squared
 from its orginal Amplitude format (see keyword Amplitude).  Generally,
 SAR data is available in either Amplitude or power format, however the
 most common format is Amplitude.  In order to go from Amplitude to Power
 the data is squared and in order to go from Power to Amplitude, the data is
 squared rooted.  Power images can also be referred to Intensity images.


1    Principal components
@keyword{Principal components}

 A method of analyzing multivariate data in order
 to express their variation in a minimum number of principal component or
 linear combinations of the original, partially correlated variables.


1    Principal point
@keyword{Principal point}

 Is the point where a perpendicular projected through the centre of the camera
 lens intersects the photo image. It is the geometric centre of the photo and
 is assumed to coincide with the intersection of the x and y axes. The
 principal point can be located on a single photo by the intersection
 of lines drawn between opposite side or corner fiducial marks.


1    Print
@keyword{Print}

 (1) To generate output to be printed on paper by a printer.
 (2) to generate output in printer format for a screen or file.


1    Printer
@keyword{Printer}

 An output device that converts information to a printed page. Various
 types of printers area available, including dot-matrix, laser, ink jet,
 daisywheel, chain, thermal, and drum-type.


1    Probability
@keyword{Probability}

 In classification, probability is a statistical estimate of the
likelihood that a given pixel is a member of a particular class or category.


1    Procedure
@keyword{Procedure}

 (1) A method or recipe for performing an item of work.
 (2) A set of EASI commands in a file.


1    Projection, map
@keyword{Projection, map}

 A systematic drawing of lines on a plane surface to represent the parallels
 of latitude and the meridians of longitude of the earth or a section of the
 earth. A map projection may be established by analytical computation or may
 be constructed geometrically.


1    Pseudo-colour memory
@keyword{Pseudo-colour memory}

 A memory in video displays that will
 allow mapping of a selection of grey values to colour values.

1    Public domain
@keyword{Public domain}

 Software for which ownership has been transferred to the
 public. It has no ownership or distribution restrictions.


1    Pulldown menu
@keyword{Pulldown menu}

 A window that appears from the top of the screen downward.
 A pulldown menu is activated when the user selects the menu title from the
 main menu bar. The user can use a mouse or the cursor to highlight the
 available pulldown menu options. When the desired option is highlighted, the
 user double-clicks the mouse or presses Enter/Return.


1    Pushbroom scanner
@keyword{Pushbroom scanner}

 A new generation sensing system that forms images without moving optics
 (e.g., scanning mirror) and offers high spatial and spectral resolution.
 A pushbroom scanner employs numerous and very small solid-state detector
 elements that are closely packed in one-dimensional linear arrays orthogonal
 to the flight path. There is typically one array for each spectral band.


1    Radar
@keyword{Radar}

 (1) The principle of locating targets or objects by the measurement of
 reflections of radio-frequency energy from them. (2) A term applied to devices
 and systems that make use of this principle. Acronym for radio detection and
 ranging.


1    Radar, imaging
@keyword{Radar imaging}

 An active remote-sensing device that transmits pulses of
 microwave energy and then receives reflections of the signal from a target. The
 reflected component is called the echo or backscatter.


1    Radar detection
@keyword{Radar detection}

 A measure of the smallest object that can be discerned in a
 radar image as a result of its ability to reflect microwave energy.


1    Radar resolution
@keyword{Radar resolution}

 The minimum ground separation between two targets of equal reflectivity
 that will enable them to appear individually in a processed radar image.


1    Radiometer
@keyword{Radiometer}

 An instrument for quantitatively measuring the intensity of
 electromagnetic radiation in some band of wavelengths in any part of the
 electromagnetic spectrum. Usually used with a modifier, such as an infrared
 radiometer or a microwave radiometer.


1    Radiometric correction
@keyword{Radiometric correction}

 Correcting gain and offset variations in MSS data. Procedure calibrates and
 corrects the radiometric data provided by the Landsat sensor detectors.


1    RAM (Random Access Memory)
 @keyword{RAM}

 See also: {|}Memory


1    Range
@keyword{Range}

 A measure of dispersion equivalent to the difference between the
 largest and smallest value in a set of observations.


1    Range, dynamic
@keyword{Range, dynamic}

 The ratio of maximum measurable signal to minimum detectable signal.
 The upper limit usually is set by saturation and the lower limit by noise.


1    Raster
@keyword{Raster}

 The pattern of horiaontal, parallel scan lines comprising the image on
 a CRT screen, on which wach scan line consists of segments varying in
 intensity. Raster data thus refers to data in the form of parallel-line
 segments or grid cells.


1    Raster-to-vector
@keyword{Raster-to-vector conversion}

 The process of converting an image made up of cells into
 one described by lines and polygons.


1    Rational number
@keyword{Rational number}

 A quantity that can be represented exactly as the ratio of two integers.


1    README file
@keyword{README}

 A text file accompanying distributed software, meant to be read before the
 software is set up or installed. The text may explain the other files
 in the package and convey instructions for proceeding.

 A README file is useful for conveying information specific to a particular
 software release. therefore, such information may be only temporarily
 accurate, and not intended as a permanent manual for subsequent releases.


1    Record
@keyword{Record}

 A group of items in a file treated as a unit. For example, all data items
 for a census tract can be grouped as a record ans assigned to a single segment
 of a magnetic tape file for convenient storage and retrieval.

1    Rectification
@keyword{Rectification}

 The process of removing from an aerial photograph the distortion caused by
 tilt, which occurs when the optic axis of the camera is not
 truly perpendicular to the horizontal plane.


1    Reflectance
@keyword{Reflectance}

 The ratio of the radiant energy reflected by a body to that incident upon it.
 The suffix (-ance) implies a property of that particular specimen surface.


1    Reflection (EMR theory)
@keyword{Reflection (EMR theory)}

 EMR neither absorbed nor transmitted is reflected. Reflection may be diffuse
 when the incident radiation is scattered upon being reflected from the surface, or specular,
 when all or most angles of reflection are equal to the angle of incidence.


1    Registration
@keyword{Registration}

 The process of geometrically aligning two or more sets of image data such that
 resolution cells for a single ground area can be digitally or visually
 superposed. Data being registered may be of the same type, from very different
 kinds of sensors, or collected at different times.


1    Relational operator
@keyword{Relational operator}

 An operator that compares two values or expressions.
 The relational operators most commonly used in programming and the
 symbols that represent them in most programming languages include the
 following:

 Operator            Symbol
 Equal            =
 Not equal            <>
 Greater than            >
 Less than            <
 Greater than or equal            >+
 Less than or equal             <+


1    Remote sensing
@keyword{Remote sensing}

 In the broadest sense, the measurement or acquisition of information of some
 property of an object of phenomenon, by a recording device that is not in
 physical or intimate contact with the object or phenomenon under study;
 e.g., the utilization at a distance (as from an aircraft, spacecraft or ship)
 of any device and its attendant display for gathering information pertinent
 to the environment, such as measurements of force fields, electromagnetic
 radiation, or acoustic energy. The technique employs such devices as the
 camera, lasers, and radio frequency receivers, radar systems, sonar,
 seismographs, gravimeters, magnetometers, and scintillation counters.


1    Report
@keyword{Report}

 A file containing a set of related outputs fro an application system,
 designed to be understood easily by people. A report can either be printed on
 paper (hard copy) or viewed on a display device (soft copy).


1    Resampling
@keyword{Resampling}

 Technique for transforming a raster image to a particular scale
 and projection.


1    Resolution
@keyword{Resolution}

 The ability of an entire remote sensor system, including lens, antennae,
 display, exposure, processing, and other factors, to render a sharply defined
 image. It may be expressed as line pairs per millimeter or meter, or in many
 other ways. For infrared line scanners the resolution may be expressed as
 the instantaneous field of view.


1    Resolution cell
@keyword{Resolution cell}

 The smallest area in a scene considered as a unit of data. See Pixel.


1    Return beam vidicon (RBV)
@keyword{Return beam vidicon (RBV)}

 A modified vidicon television camera tube, in which the output signal is
 derived from the depleted electron beam reflected from the tube target. The
 RBV can be considered as a cross between a vidicon and an orthicon. RBVs
 provide highest resolution TV imagery, and are used in the ERTS (Landsat)
 series.


1    Rewind
@keyword{Rewind}

 To position a sequential file at the beginning, ready to read or write
 the first record. For a file on magnetic tape, rewinding is a physical
 operation. For a file on a direct access medium such as a disk, the operation
 involves only resetting a record position counter.


1    RGB monitor
@keyword{RGB monitor}

 A monitor that accepts separate signals for the primary colours
 red, green, and blue, to produce various colours on the screen.


1    Roll
@keyword{Roll}

 Rotation of an aircraft about the longitudinal axis to
 cause a wing-up or wing-down attitude.


1    ROM
@keyword{ROM}

 An acronym for read only memory, a microcircuit containing programs
 or data that cannot be erased. When new data or programs can replace old ones,
 the microcircuit is called EROM, for erasable read-only memory, or a PROM,
 for programmable read-only memory.


1    Root directory
@keyword{Root directory}

 The highest-level directory on a disk volume. In MS-DOS and
 similar systems, the root directory is unnamed.


1    Rotation
@keyword{Rotation}

 In graphics, a mathematical transformation of the coordinates of each pixel
 in a graphics image, to give the effect of having displaced the image
 by some angle about the centre of its axis system.


1    Run-length Encoding
@keyword{Run-length Encoding}

 A compact method of storing data in raster databases.


1    Sample
@keyword{Sample}

 A subset of a population selected to obtain information
 concerning the characteristics of the population.


1    Sampling rate
@keyword{Sampling rate}

 The temporal, spatial, or spectral rate at which
 measurements of physical quantities are taken. Temporally,
 sampling variables may describe how often data are collected or
 the rate at which an analog signal is sampled for conversion to
 digital format; the spatial sampling rate describes the number,
 ground size, and position of areas where spectral measurements
 are made; the spectral sampling rate refers to the location and
 width of the sensor's spectral channels with respect to the
 electromagnetic spectrum.


1    Satellite
@keyword{Satellite}

 A man-made object that revolves about a spatial body.


1    Saturation
@keyword{Saturation}

 Degree of intensity difference between a colour and
 an achromatic light-source colour of the same brightness.


1    Scale
@keyword{Scale}

 The ratio of a distance on a map to its corresponding distance on the ground.
 Scale may be expressed as a ratio, 1:24,000; a representative fraction,
 1/24,000; or an equivalence, 1 inch = 2,000 ft.


1    Scan line
@keyword{Scan line}

 The narrow strip on the ground that is swept by the
 instantaneous field of view of a detector in a scanner system.


1    Scanner
@keyword{Scanner}

 Any device that scans, and thus produces an image.


1    Scattering
@keyword{Scattering}

 (1) The process by which small particles suspended
 in a medium of a different index of refraction diffuse a portion
 of the incident radiation in all directions. (2) The process by
 which a rough surface reradiates EMR incident upon it.


1    Scene
@keyword{Scene}

 In a passive remote sensing system, everything occurring
 spatially or temporally before the sensor, including the Earth's
 surface, the energy source, and the atmosphere, that the energy
 passes through as it travels from its source to the Earth and
 from the Earth to the sensor.


1    Scientific notation
@keyword{Scientific notation}

 A conventional representation for printing real numbers
 especially very large or very small numbers, as a mantissa (usually between 1.0
 and 9.999) and an exponent (power of 10). Thus, 12345670000000 is written
 as 1.234567 x 10 13 or in EASI/PACE notation 1.234567e13.


1    Scratch graphic
@keyword{Scratch graphic}

 A temporary graphic layer, used by a program to display
 intermediate calculations/information and erased or released after use of the
 program is complete.


1    Scroll
@keyword{Scroll}

 To move text or images vertically (or less often horizontally) through
 a screen or through a window. Many programs support user-controlled
 scrolling, in which the user manipulates either a scroll bar or cursor keys to
 view different parts of a file, a list, or an image. The effect is as if the
 window itself were moving over a large, stationary document.


1    Scroll bar
@keyword{Scroll bar}

 A control facility, especially in a graphical user interface (GUI),
 that enables the user to scroll information on the screen by using a pointing
 device such as a mouse.

 A scroll bar has an up arrow on the top, a down arrow at the bottom at each
 end, and a block in the middle called the scroll thumb. The user can either
 click on the up or down arrows to move the screen slowly in either direction
 or drag the scroll thumb quickly to a position corresponding to a position in
 the file or list being scrolled. Many list boxes provide scroll bars, enabling
 the users to move through lists that are too long to fit in the window.


1    Sensitivity
@keyword{Sensitivity}

 The degree to which a detector responds to electromagnetic energy incident
 upon it.


1    Segment
@keyword{Segment}

 A place of storage on a PCIDSK image database
 file for ancillary data other than image data.


1    Sensor
@keyword{Sensor}

 Any device that gathers energy, EMR or other, converts it into a signal and
 presents it in a form suitable for obtaining information about the environment.


1    Serial port
@keyword{Serial port}

 An interface between a computer's input-output (I/O) circuitry
 and a serial device. Personal computers typically have two or more serial
 ports, used for a modem, a mouse, or less often, a printer.

 Serial ports contain buffers and circuitry, usually a UART (universal
 asynchronous receiver transmitter), that convert a byte to a series of bits and
 add parity and framing bits. The receiving serial port reverses the process and
 presents the reconstructed byte to the receiving computer's I-O system.

1    Set
@keyword{Set}

 An unordered collection of data items.


1    Shareware
@keyword{Shareware}

 Software distributed over public networks or by other means, and provided
 to users free of charge so that they can try it before buying it. After
 deciding to keep a shareware program, the user is expected to forward a fee
 to the developer. In exchange for this payment, the developer often provides
 additional documentation and free upgrades to the product. PC File, PC Write,
 and PC Talk are examples of popular shareware programs. Although
 shareware is available to the public, the developer retains ownership and may
 pursue rights under copyright law.


1    Side lap
@keyword{Side lap}

 The overlap between photographs in adjacent parallel strips.


1    Signature
@keyword{Signature}

 Any characteristic or series of characteristics by which a material may be
 recognized in an image, photo, or data set.

 See also: {|}Spectral signature

1    Signature analysis techniques
@keyword{Signature analysis techniques}

 Techniques that use the variation in the spectral reflectance or emittance
 of objects as a method of identifying the objects.


1    Signature extension
@keyword{Signature extension}

 The use of training statistics obtained from one geographical area to
 classify data from similar areas some distance away; includes consideration
 of changes in atmosphere, and other geographical and temporal conditions that
 can cause differences in signal level for signal classes of interest.

 See also: {|}Spectral signature, {|}Drift


1    Sine
@keyword{Sine}

 The ratio between the side opposite a specified acute angle in a right
angled triangle and the hypotenuse.

1    Signed integer
@keyword{Signed integer}

 An integer interpreted as either positive or negative. In binary
 representations, the first bit of a word conventionally represents plus (0) or
 minus (1), and the remainder of the word represents its magnitude.


1    Skewness
@keyword{Skewness}

 The third moment about the mean, indicates whether a distribution
 is symmetrical or lopsided. The locations of the mode, median and mean all
  n the case of symmetrical distributions, but they diverge when
 skewness is present.


1    Slope
@keyword{Slope}

 The rate of change of elevation data values as a function of distance. (PCI)

 EASI/PACE program SLP calculates the slope of elevation at each pixel.


1    Smoothing
@keyword{Smoothing}

 The averaging of densities in adjacent areas to produce more gradual
 transitions.


1    Soft copy
@keyword{Soft copy}

 A temporary image of a map or diagram or text report. for example,
 on the screen of a CRT display.


1    Software
@keyword{Software}

 The computer programs that drive the hardware components of a
 data processing system; includes system monitoring programs, programming
 language processors, data handling utilities, and data analysis programs.


1    Source code
@keyword{Source code}

 A sequence of statements in a programming language. Source
 code is written by a programmer, and can be read by human beings and
 processed by a compiler (an assembler or interpreter).


1    Spatial filter
@keyword{Spatial filter}

 An image transformation. An operator used to
 lessen noise or enhance certain characteristics of the image. For any
 particular (x,y) coordinate on the transformed image, the spatial
 filter assigns a grey shade on the basis of the grey shades of a
 particular spatial pattern near the coordinates (x,y).


1    Spatial information
@keyword{Spatial information}

 Information conveyed by the spatial variations of spectral response
 (or other physical variables) present in the scene.


1    Spectral band
@keyword{Spectral band}

 An interval in the electromagnetic spectrum
 defined by two wavelengths, frequencies, or wavenumbers.


1    Spectral reflectance
@keyword{Spectral reflectance}

 The reflectance of electromagnetic energy at specified wavelength intervals.


1    Spectral response
@keyword{Spectral response}

 The response of a material as a function of wavelength to incident
 electromagnetic energy, particularly in terms of the measurable energy
 reflected from and emitted by the material.


1    Spectral signature
@keyword{Spectral signature}

 Quantitative measurement of properties of an
 object at one or several wavelength intervals.


1    Spectrum library file
@keyword{Spectrum library file hyperspectral}

 A binary file containing a series of records, each of which represents
 the reflectance (or radiance) values for a particular ground feature.
 These reflectance spectra have very high spectral resolution (on the
 order of 10 nanometres) and consist of measurements in many wavelength
 locations (generally between 224 nd 900 information channels).


1    SPOT
@keyword{SPOT satellite}

 Systme Probatoire d'Observation de la Terre - an earth resource satellite
 with high resolution sensors launched by France in January 1986.


1    Stand-alone program
@keyword{Stand-alone program}

 A PCI software product which is operational without the simultaneous
 presence of EASI/PACE. To-date PCI's list of stand-alone products include:
 FLY!, RADARsoft, RE*GENESIS, ImageWorks and GCPWorks.


1    Standard deviation
@keyword{Standard deviation dispersion variance}

 The most commonly used measure of statistical dispersion and is calculated
 as the square root of the vaiance.

 See also Variance.


1    Steropair
@keyword{Stereopair}

 Two adjacent aerial photographs designed to yield a three-dimensional
 effect when the two images are viewed in stereo.


1    Stereoscopy
@keyword{Stereoscopy}

 The science and art that deals with the use of binocular vision
 for observation of a pair of overlapping photographs or other perspective
 views, and with the methods by which such viewing is produced.


1    Storage volume
@keyword{Storage volume}

 (1) A unit of physical storage (such as a disk pack, hard drive, magnetic tape, or even a floppy disk). (2) A logical unit of storage. This
 type of volume is not bound by the physical limitation of the device and may
 span several storage devices. For example, Novell enables you to address
 several hard drives on the server as one volume of storage.


1    String
@keyword{String}

 A data type comprising a sequence of characters (or less commonly, a
 sequence of bits).


1    Subdirectory
@keyword{Subdirectory}

 In a hierarchial file system, a directory that is a subordinate to
 another directory.


1    Subtractive colour process
@keyword{Subtractive colour process}

 A method of creating essentially all colours through the subtraction of
 light of the three subtractive colour primaries (cyan, magenta and yellow)
 in various proportions through use of a single white light source.


1    Sun synchronous
@keyword{Sun synchronous}

 An Earth satellite orbit in which the orbital plane is near polar and the
 altitude such that the satellite passes over all places on Earth having the
 same latitude twice daily at the same local sun time.


1    Supervised classification
@keyword{Supervised classification}

 A computer-implemented process through which each measurement vector is
 assigned to a class according to a specified decision rule, where the possible
 classes have been defined on the basis of representative training samples of
 known identity.


1    SVGA (Super Video Graphics Array)
@keyword{SVGA}

 An enhanced form of VGA that provides the capability to display a higher
 resolution and a wider range of colours than does VGA technology. SVGA can
 produce a resolution of 1024x768 or greater. For a system to function with
 enhanced capability, both the video adapter and the monitor must support SVGA.


1    Swath width (total field of view)
@keyword{Swath width (total field of view)}

 The overall plane angle or linear ground distance covered by a multispectral
 scanner in the across-track direction.


1    Synchronous satellite
@keyword{Synchronous satellite}

 An equatorial west-to-east satellite orbiting the Earth at an altitude of
 34,900 km, at which altitude it makes one revolution in 24 hours, synchronous
 with the Earth's rotation.


1    Syntax
@keyword{Syntax}

 The rules specifying the form of statements used in a given language,
 and how the statements may be combined. Any violation of these rules is called
 a syntax error.


1    Tablet
@keyword{Tablet}

 A rectangular pad with a controlling device like a pen or puck
 that reports about the location of the controlling device. Generally used
 to move a cursor.


1    Tail trimming
@keyword{Tail trimming}

 Ignores a user-defined percentage of values at each extreme (tail) of a
 distribution. For example, if a 2% tail trim is requested prior to
 performing a contrast stretch, then 2% of the highest and 2% of the lowest
 values in the collection of values (image pixel values) will be ignored prior
 to the contrast stretch calculation.


1    Target
@keyword{Target}

 (1) An object on the terrain of specific interest in a remote sensing
 application. (2) The portion of the Earth's surface that produces by reflection
 or emission the radiation measured by the remote sensing system.


1    Tape
@keyword{Tape}

 A sequential auxiliary storage medium that consists of a long strip of
 magnetic material which can record data when moved across the write head of
 a tape drive. One side oft he tape is coated with a ferromagnetic material that
 can record information.

 The declining cost of more flexible disk storage has nearly eliminated the use
  tape for master files and temporary files, except for extremely high volume
 batch processing. Today tape is used mainly for archive files and backup files.

1    Temporary file
@keyword{Temporary file}

 A file created and used in a job (job step or process) and
 discarded at the end of that job; same as scratch file or work file.
 The continuing increase in available memory has eliminated the need for all
 but the largest temporary files. Programs can now store data records in arrays
 or other internal data structures rather than writing them to a file and reading
 them back. This not only improves performance, but in many cases also
 simplifies program logic. Some of the expected performance gain on smaller
 machines, however, may be list in the behind-the-scenes input-output
 operations required for virtual paging.


1    Terminal
@keyword{Terminal}

 A device for communicating with a computer, and usually including
 a keyboard and either a CRT display or printer.


1    Texture
@keyword{Texture}

 In an image, the frequency of change and arrangement of tones.
 Some descriptive adjectives for textures are fine, medium or coarse;
 and stippled or mottled.


1    Thematic image
@keyword{Thematic image}

 An image whose grey values represent information relating to specific
 themes such as population density, crop type, or land use, etc.

 Channels 6 and 7 of the Training Data Set file /pic/demo/irvine.pix are
 examples of thematic images.


1    Threshold
@keyword{Threshold}

 The boundary in spectral space beyond which a data
 point, or pixel, has such a low probability of inclusion in a
 given class that the pixel is excluded from that class.


1    TIFF (Tagged Image File Format)
@keyword{TIFF}

 A standard format developed by Aldus and Microsoft for efficiently storing
 graphic images. TIFF files are labelled with the extension .tif


1    Tilt
@keyword{Tilt}

 The angle between the optical axis of the camera and the plumb line for a
 given photo.


1    Tone
@keyword{Tone}

 Each distinguishable shade of grey from white to black on an image.


1    Trackball
@keyword{Trackball}

 A device with an embedded revolving ball that provides manual control
 of a cursor.


1    Training
@keyword{Training}

 Informing the computer system which image areas to
 analyze for spectral properties or signatures of specific land cover
 classes; also called signature extraction.


1    Training data set
@keyword{Training data set}

 A number of PCIDSK format files supplied with the EASI/PACE software and
 intended for experimentation and learning. These files are located in the
 directory /pci/demo .


1    Training samples
@keyword{Training samples}

 The data samples of known identity used to determine decision boundaries
 in the measurement of feature space prior to classification of the overall
 set of data vectors from a scene.


1    Training sites
@keyword{Training sites}

 Recognizable areas on an image with statistical properties useful for
 identifying other similar areas.


1    Translation
@keyword{Translation}

 The relocation of a figure while maintaining the same angular
 orientation to the system of coordinate axes.


1    Transverse Mercator
@keyword{Transverse Mercator}

 A conformal conical projection with one meridian and two standard parallels.


1    Tree structure
@keyword{Tree structure}

 The ordering of data items in a hierarchial list whereby each
 item is linked directly to one item above it and several items below it.


1    Truncation
@keyword{Truncation}

 (1) The dropping of any value to the right of the decimal point.
 (2) Rounding values that are too large or too small to be stored in a
 specific channel type (e.g. an 8-bit unsigned channel) to the maximum and/or
 minimum allowable values for the type of channel (e.g. 255 or 0).


1    TSR (Terminate and Stay Resident)
@keyword{TSR}

 A type of program that can remain in memory after it is terminated, then be
 activated when needed.


1    Turnkey
@keyword{Turnkey}

 An adjective used to describe a computer system consisting both of
 hardware and software that is delivered ready for immediate operation.


1    Underflow
@keyword{Underflow}

 A condition in which a value is too small to be represented in a
 word in memory, for example, when a program attempts to store the computed
 result 0.1 x 10-105 in a word not able to accept a negative exponent below -63.


1    Ultraviolet radiation (UV)
@keyword{Ultraviolet radiation UV}

 Electromagnetic radiation of shorter wavelength than visible radiation
 but longer than X-rays; roughly radiation in the wavelength interval
 between 10 and 4000 Angstroms.


1    um
@keyword{um micrometre micrometer micron}

 An abbreviation for the unit of measure known as the micrometre or micron.
 1 micrometre equals 0.000001 metres.


1    UNIDSK
@keyword{UNIDSK}

 A file format used by CCRS, and older PCI (V3.2 and below) and
 others to store image and associated data.


1    Unimodal
@keyword{Unimodal}

 See also: {|}Mode

1    Union
@keyword{Union}

 The set containing all objects belonging to one or the other, or both, of
 two sets. Formally, x is an element of the union of set A and set B, if,
 and only if, x is an element of A, or x is an element of B.


1    UNIX
@keyword{UNIX}

 A multiuser, multitasking operating system that runs on several
 hardware platforms, including VAX and Intel. Developed by AT&T Bell
 Laboratories in the late 1960s, UNIX was the first large program written in C.


1    Uppercase
@keyword{Uppercase}

 The capitalized alphabetic characters, A through Z.


1    User-friendliness
@keyword{User-friendliness}

 The quality of software that is designed to be easy to use and easy to learn.
 User-friendly software usually provides extensive help features. Context
 sensitive help enables the program to determine what the user is currently
 doing and what help the user needs at the time. User-friendly instructions also
 result in better usage of the software. Users consider graphical user
 interfaces (GUIs), and applications running under GUIs, as user-friendly
 because the interface is attractive and consistent.


1    Value
@keyword{Value}

 The degree of lightness or darkness of a colour.


1    Variance
@keyword{Variance}

 It is a measure of the dispersion of the individual unit values about
 their mean and is computed by calculating the average of the squared
 deviations about the mean.


1    Vector
@keyword{Vector}

 A quantity having both magnitude and direction.


1    Vertical exaggeration
@keyword{Vertical exaggeration}

 An increase or decrease in the vertical dimension of the perceived stereo
 model when compared to its horizontal dimension ratio of the actual object.


1    VGA (Video Graphics Array)
@keyword{VGA}

 An IBM video display standard first introduced with the PS/2 line of desktop
 computers.

 VGA provides a standard resolution for text and graphics and is currently
 considered the minimum standard for most Intel-based microcomputers. A
 VGA adapter and monitor are analog devices, and can support software that
 used the older CGA and EGGA modes. In addition, VGA can display up to 640
 x 480 with 16 colours. Advanced VGA adapters, called SVGA (super video
 graphics array) adapters, can display 600 x800, 1024 x 768, and even 1280 x
 1280, with an almost unlimited array of colours.


1    vi
@keyword{vi}

 The standard UNIX-based, screen-oriented (visual) display text editor.
 The vi editor is supported on virtually all UNIX versions, and was designed to
 support C programmers. The vi editor has been widely criticized as being
 extremely error-prone and not user-friendly, and has now been eclipsed by the
 newer UNIX editor, emacs.


1    Video
@keyword{Video}

 A device that uses a lighted screen, such as a television screen or a
 computer monitor, to provide viewable information.


1    Virtual memory
@keyword{Virtual memory}

 The capability to simulate more memory than actually exists on the computer
 by swapping portions of an address space between real memory and disk.


1    Virtual reality
@keyword{Virtual reality}

 The use of technology to create the illusion that the user is actually
 occupying an artificial space that he or she can observe and interact with.
 To be convincing, virtual reality requires an immense amount of computer
 power. Furthermore, the extremely complex algorithms needed to simulate
 many forms of interaction are still the subject of research. It is doubtful,
 therefore, that virtual reality will have widespread practical application in
 the 1990s. In limited forms, however, it has already been implemented in arcade
 games and training devices such as flight simulators and flight combat training
 equipment.

 The available memory appears very large to the program, even if the real
 memory is comparatively small. The operating system divides into small
 portions called pages to enable the sections to be swapped more easily in and
 out of memory.

 See also: {|}Paged memory


1    VMS (Virtual Memory System)
@keyword{Virtual Memory System}

 The principal operating system for Digital Equipment Corporation's VAX
 computers. VMS is widely used in support of academic computing, as well as
 some mid-range applications. Although VMS is generally admired for its
 efficiency and ease of use, its future is in doubt due to the emergence of
 UNIX on the same hardware.


1    Volatile memory
@keyword{Volatile memory}

 Memory that does not retain information after the system's
 power is shut off. Random-access memory (RAM) is usually volatile memory.
 In contrast, media (such as the system ROM BIOS) that maintain information
 when the power is shut off are nonvolatile.


1    Volume label
@keyword{Volume label}

 A machine-readable label record at the beginning of a tape reel
 or disk uniquely identifying that tape or disk.

 A volume label usually contains a serial number, and may contain information
 about the manufacturer or the date the volume was put into service. Unlike a
 data set label, it remains unchanged over the lifetime of the tape or disk
 volume.

 In a computer centre that has a large library of magnetic tapes or dismountable
 disks, the volume serial number is usually the main key to both rack storage
 and file cataloging.

 MS-DOS provides both an unchanging serial number record and an 11-
 character label record that you can change by using the LABEL command.

1    VT-100 terminal
@keyword{VT-100 terminal}

 A DEC terminal consisting of a CRT (cathode ray tube) and
 keyboard. The VT-100 is widely used in online systems of the 1980s and is still
 emulated in many desktop computer telecommunications applications.


1    Wavelength
@keyword{Wavelength}

 The distance from one wave peak to the next. In remote sensing,
 it is common to categorize electromagnetic energy waves by their wavelength.
 The most prevalent unit used to measure wavelength along the spectrum is the
 micrometer (um).


1    Weight
@keyword{Weight}

 In image processing operations, a value assigned to each image grey
 value as an indication of its relative importance, or its intended
 contribution to the resultant image.

 EASI/PACE programs IND and RTR have parameters that offer weight factors.


1    Wild card
@keyword{Wild card}

 A variable symbol - the asterisk (*) used by PCI - in a search string
 that will match a variable number of characters in the corresponding position.
 For example, if you were using the LOCATE utility of Xpace to search for the
 program the merges signatures, you could use wild cards as follows:

 Search string = *MERG*

 This would return a list of all programs that contained the string MERG. If you
 knew that the program started with \`SIG\', you could have entered SIG* for the
 search string.


1    Window
@keyword{Window}

 A rectangular portion of a larger mapped area selected for display,
 for example, a rectangle surrounding Poland and ignoring most other areas in
 a database covering eastern Europe. (

 In EASI/PACE, windows of interest within a file or video display are defined
 by using one of the following parameters: MASK, DBIW, DBOW, VDOW, VDIW.


1    Windows
@keyword{Windows}

 A system software product for MS-DOS, introduced in the mid-1980s by the
 Microsoft Coprporation, that provides an environment for other
 programs, basesd on the following: (1) multiprogramming, (2) a graphical user
 interface (GUI) in which each executing program is associated with its own
 application windows, (3) dynamic data excahnge between two independent
 (4) management of the hardware configuration, including memory
 and devices and (5) output spooling.

 Although Windows is not an operating system, users often characterize it as
 such, because Windows and MS-DOS together provide the range of functions
 normally considered as those of an operating system. Its main competition comes
 from complete operating systems such as OS/2, Windows NT, and UNIX. (CPD)

1    Windows NT
@keyword{Windows NT}

 An operating system form Microsoft, released in 1993 and intended to compete
 on large Intel computers and network configurations with OS/2 and UNIX.

 Windows NT is not an improved version of Microsoft Windows, but a
 completely new operating system. It shares with Windows only the name and
 a similar interface. Like OS/2, Windows NT supports emulation of
 applications written for MS-DOS and for Windows.


1    Workaround
@keyword{Workaround}

 Any method of circumventing a problem or bug without correcting it.


1    WYSIWYG
@keyword{WYSIWYG}

  WYSIWYG = What You See Is What You Get

 A property of software in which the output displayed on the user's screen
 looks very similar to the eventual hard copy or printed output, with respect
 to page layout, fonts, and graphics. It is considered a desirable
 characteristic in word processing and spreadsheet software.

1    xor
@keyword{xor}

 A binary logical operator that is assigned the value of true only if one (but
 not more than one) of its operands is true.


1    X Window
@keyword{X Window}

 A graphical user interface (GUI) for UNIX.

 The X Window windowing environment uses a graphical workstation, called
 an X Terminal, and a mouse. Using the client-server model over a network, X
 Window can display on workstation screens the graphics generated on a server.
 Sometimes both the client and the server portions of X Window can be
 maintained within the same computer.

 Most versions of UNIX support X Window. In addition, DOS-based X
 Terminals are available to display graphics on DOS workstations connected
 a network to a UNIX server.

1    Yaw
@keyword{Yaw}

 Rotation of an aircraft about its vertical axis, causing
 the longitudinal axis to deviate from the flight line.

1    ZIP file
@keyword{ZIP file}

 A file created and read by compression programs produced by PKware, Inc.
 Compressing a file significantly reduces its size, perhaps by as much as 90
 percent, depending on content. This compression reduces software production
 and line costs for data transmission.

 Virtually all BBS (bulletin board systems) files are in a compressed format.
 ZIP files can be produced in a self-extracting executable form, well-suited
 to software distribution.

 See also: {|}PKZIP


1    Zoom
@keyword{Zoom}

 A capability for proportionately enlarging or reducing the scale of an
 image displayed on a CRT.