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GM_ProjectPointAtElev

This function projects a point from one coordinate system to another at some elevation above the ellipsoid. Use this instead of GM_ProjectPoint if you need to do extremely precise conversions at some height above the ellipsoid. The typical difference between conversions at the ellipsoid surface and within a few thousand meters of the surface is less than 1 meter. If NULL is passed for either projection parameter, the current view/export projection will be used. This function provides an easy way to convert from latitude/longitude coordinates (or coordinates in any other supported projection) to any other projection, including the current view projection.

For examples on how to set up projection definitions, see the documentation for the GM_SetProjection function.

Syntax
GM_Error_t32 GM_ProjectPointAtElev
(
double                  aXIn,       // IN: X coordinate of input point
double                  aYIn,       // IN: Y coordinate of input point
double*                 aXOut,      // OUT: X coordinate of output point
double*                 aYOut,      // OUT: Y coordinate of output point
const GM_Projection_t*  aProjIn,    // IN: projection to convert from (NULL for current)
const GM_Projection_t*  aProjOut,   // IN: projection to convert to (NULL for current)
double                  aElev       // IN: elevation in meters above ellipsoid surface to do conversion at
);