The program may be employed for any spherical system. Longitude and latitude values are measured in floating-point degrees. The arguments requested by the program are:
Not all of these parameters are required by each projection. Here is a list of those actually used:
Proj. Description Parameters Required 1 Rectangular BLAT, BLON, ELAT, ELON 2 Mercator BLAT, BLON, ELAT, ELON 3 Polar Equidistant BLAT 4 Orthographic Equatorial CLAT, CLON 5 Orthographic Polar BLAT 6 Azimuthal Equidistant CLAT, CLON 7 Perspective BLAT, BLON, ELEV, ELAT, ELON 8 Cylindrical Equal Area BLAT, BLON, ELAT, ELON
The usual cartographic convention is adopted that latitude runs from -90 degrees at the South Pole through 0 at the Equator to +90 degrees at the North Pole, and that longitude runs from 0 degrees through Greenwich, England, eastward to 180 degrees in the Pacific Ocean and back to Greenwich at 360 degrees. Longitude is thus synonomous with East Longitude; West Longitude can be considered a negative value which when incremented by 360 degrees becomes East Longitude.
The map projection routines will internally automatically adjust longitudes in the interval [-360 to 720] to the interval [0 to 360]; latitude values are assumed to be confined to the interval [-90 to +90]. Unpredicatable results may occur if this convention is not adhered to.
A. V. Hershey, "Terrestrial and Celestial Cartography", Report NSWC/DL TR-3789, May 1979, Naval Surface Weapons Center, Dahlgren, VA 22448.
William D. Johnson, "Computer Generated Maps. Part I", pp. 10-12, 76-101, Byte Magazine, Vol. 4, No. 5 (May 1979), and "Computer Generated Maps. Part II", pp. 100-123, ibid, No. 6 (June 1979).
J. E. Jackson, "Sphere, Spheroid and Projections for Surveyors", Granada Publishing Ltd. (1980).