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OZGIS80.TUT
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OzProj is a program is that will process a geographic file to form a new
geographic file converting either from (Longitude,Latitude) to a projection
or in the reverse direction. Hence conversion from one projection to
another has to take place in two steps.
Often projections will not be of concern, as map data will be used as supplied.
However, if data comes from several sources in different projections the files
may have to be converted to a common coordinate system.
You will have to have a basic knowledge of the projection you want to use
e.g. that AMG is UTM with the Australian Spheroid and a false origin
(500000,10000000).
The parameters of the projection are stored in the geographic file. When the
data are first entered the projection is usually set to 'undefined', unless it
is known e.g. Census boundary data are usually set to geographic (lat/long
units degrees).
The first operation is often to define the projection of a new geographic file
and store the parameters in the file header.
Vertices are stored in single precision in OzGIS (there is not enough memory on
the PC to do anything else). This means an accuracy of seven digits, so some
values may not be accurate e.g. UTM may be a few metres out. If more precise
values are required, you may have to define your own false origin.
Latitude / longitude data must be given with units degrees.
Latitudes are negative in the Southern hemisphere.
Usual value ranges are:
Longitude -180 to +180
Latitude -90 to +90
Note that the X value in data files is the longitude.
examples: (-100.0,50.0) i.e. longitude -100, latitude 50
(145.0, -42.0) a point in Tasmania
Several projections are supported:
Albers Conical Egual Area
Azimuthal equidistant
Equidistant Conic
Equirectangular
Gnomic
Lambert Conformal Conic
Lambert Azimuthal Equal Area
Mercator
Miller Cylindrical
Orthographic
Polyconic
Stereographic
Transverse Mercator
Sinusoidal
State Plane (USA) (NOT SUPPORTED YET)
Universal Transverse Mercator
Van der Grinten
Several spheroids are available. The default is either Clarke 1866 or the
6370997 metre sphere where a radius is asked for.
MERIT 1983
GRS 1980(IUGG, 1980)
IAU 1976
Airy 1830
Australian Natl, S. Amer., IAU 64
GRS 67(IUGG 1967)
Bessel 1841
Clarke 1866
Clarke 1880 mod.
Everest 1830
Hough
International 1909 (Hayford)
Krassovsky, 1942
Mercury 1960
Modified Airy
Modified Everest
Modified Merc 1968
New International 1967
Southeast Asia
Walbeck
WGS 66
WGS 72
Sphere of 6370997 m