home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Joint Education Initiative
/
Joint Education Initiative.iso
/
programs
/
dos
/
gna
/
image
/
boundary
/
coastlo
/
coastlo.doc
< prev
next >
Wrap
Text File
|
1989-03-24
|
3KB
|
58 lines
GEOPHYSICS OF NORTH AMERICA - LOW-RESOLUTION COASTLINES
coastlo.doc
This directory contains low-resolution coastlines.
These data were extracted from World Data Bank 1 and are suitable for
quickly drawing a geographic reference onto a large-scale area (like all of
the U.S). Each contiguous section of each boundary line is called a segment
and each segment is made up of some number of line fragments. Each segment
starts with an implicit move command and the fragments are the endpoints of
a series of draw commands. The data storage scheme therefore has three
basic units: regions, segments, and points (where points are the ends of
fragments).
The regionalization of the data is expressed in the file structure. The
data are stored in 6 files, each called COASTLO.NUM, where NUM is the region
number. Each data file has the longitude and latitude pairs of the
endpoints of the boundary lines for all of the boundaries within the given
region. These values are stored in two 4-byte floating point numbers.
Parameters for Low-resolution boundary Regions:
Region Minimum Minimum Maximum Maximum Number of Number of
Longitude Latitude Longitude Latitude Segments Points
0 170.1 60.3 269.7 80.1 54 4485
1 270.3 60.3 347.6 83.6 54 4830
2 172.3 28.0 253.5 59.9 58 1309
3 260.8 25.1 350.0 60.0 44 1963
4 170.8 0.0 350.0 24.8 118 2634
5 170.0 15.6 350.0 83.1 26 4772
Note: The final region covers the entire area and is, therefore opened
in every search. This region catches all of the segments which do not fit
into the other regions.
The index file (COASTLO.INX) contains information about the segments. There
is one 20 byte record for each segment. Each record contains the boundary
level for the segment (2 byte integer), the minimum longitude (degrees
east), minimum latitude, maximum longitude (degrees east), maximum latitude
of the box surrounding the segment (each a 4 byte floating point number),
and the number of points in the segment (2 byte integer). The relationship
between the index file and the data files is known through the byte offset
to the beginning of each data set in the index file. These byte offsets can
be calculated from the number of segments in each data set (20 * cumulative
number of segments).
These are the offsets in bytes to the first segment of each region in the
Low-resolution boundary index file:
Region Offset Region Offset Region Offset Region Offset Region Offset
0 0 1 1080 2 2160 3 3320 4 4200
5 6560
The region parameters and the byte offsets are contained in the file
boundary.h which is on your program disk.
The programs listindx and listdata (on the accompanying diskette) read the
index and data files respectively and output the contents to standard output
as ASCII.