The list of spheroids available is somewhat dynamic. It may not contain exactly the ones listed below. To determine the current list of possible spheroids, type in:
Spheroid | Commonly used for:| Semi-major axis| Eccentricity sqrd _____________|____________________|_________________|___________________ australian | Australia | 6378160.0 | 0.0066945419 bessel | Japan | 6377739.155 | 0.0066743722 clark66 | N. America | 6378206.4 | 0.006768658 clark80 | France, Africa | 6378249.145 | 0.0068035113 everest | India, Burma | 6377276.345 | 0.0066378466 international| Europe | 6378388.0 | 0.00672267 wgs72 | worldwide coverage| 6378135.0 | 0.006694317778
Geographic coordinates (latitude/longitude) describe the location of a point on the earth relative to the equator in the north/south directions and relative to Greenwich in the east/west directions. The same point will have different coordinates depending on the spheroid used as the approximation of the shape of the earth. The geocentric coordinates given here describe the point on the basis of the same spheroid, but they use the center of the spheroid as their origin. This can be thought of as being the center of the earth, which is why they are called "geocentric." Describing the location of a point in a spheroid requires three points: x, y, and z; these are measured out from the center along three different axes. The distances given are in meters.
This is an experimental program. It is part of initial efforts to incorporate geographic coordinates into GRASS.
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