Gets the location of the geometry point.

Returns the index of the other section point that creates a line segment with this section point. If no segment can be drawn from this point, then -1 is returned. This can happen if there is no underlying surface to determine elevation, such as a hole in a tin/dtm surface, or if the terrain is narrower than the section or the sample line, such that it's not possible to compute all elevations of the section point elevations. For valid segments, only consider segments from this point to other points of index >= 0