Given the tangent-plane coordinates of a star and the direction
cosines of the tangent point, determine the direction cosines
of the star
CALL sla_TP2V (XI, ETA, V0, V)
tangent plane coordinates of star (radians)
direction cosines of tangent point
direction cosines of star
If vector V0 is not of unit length, the returned vector V will
If vector V0 points at a pole, the returned vector V will be
based on the arbitrary assumption that at
the tangent point.
The projection is called the gnomonic projection; the
Cartesian coordinates are called
standard coordinates. The latter
are in units of the distance from the tangent plane to the projection
point, i.e. radians near the origin.
This routine is the Cartesian equivalent of the routine sla_TP2S.