**ACTION:**- Given the tangent-plane coordinates of a star and the direction
cosines of the tangent point, determine the direction cosines
of the star
(double precision).
**CALL:**`CALL sla_DTP2V (XI, ETA, V0, V)`

**GIVEN:**-

*XI,ETA***D**tangent plane coordinates of star (radians) *V0***D(3)**direction cosines of tangent point

**RETURNED:**-

*V***D(3)**direction cosines of star

**NOTES:**- 1.
- If vector V0 is not of unit length, the returned vector V will be wrong.
- 2.
- If vector V0 points at a pole, the returned vector V will be based on the arbitrary assumption that at the tangent point.
- 3.
- 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. - 4.
- This routine is the Cartesian equivalent of the routine sla_DTP2S.

Starlink User Note 67

P. T. Wallace

12 October 1999

E-mail:ptw@star.rl.ac.uk