软件包: libgeo-helmerttransform-perl (1.14-2)

Transformations between coordinates in different datums

It is usual to describe geographical points in terms of their polar coordinates (latitude, longitude and altitude) referenced to a "datum ellipsoid", which is used to approximate the Earth's geoid. The latitude, longitude and altitude of a given physical point vary depending on which datum ellipsoid is in use. Unfortunately, a number of ellipsoids are in everyday use, and so it is often necessary to transform geographical coordinates between different datum ellipsoids.

Two different datum ellipsoids may differ in the locations of their centers, or in their shape; and there may be an angle between their equatorial planes or the meridians relative to which longitude is measured. The Helmert Transform, which this module implements, is a linear transformation of coordinates between pairs of datum ellipsoids in the limit of small angles of deviation between them.