**ACTION:**- Transform tangent plane coordinates into spherical
coordinates (double precision)
**CALL:**`CALL sla_DTP2S (XI, ETA, RAZ, DECZ, RA, DEC)`

**GIVEN:**-

*XI,ETA***D**tangent plane rectangular coordinates (radians) *RAZ,DECZ***D**spherical coordinates of tangent point (radians)

**RETURNED:**-

*RA,DEC***D**spherical coordinates (radians)

**NOTES:**- 1.
- 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. - 2.
- When working in rather than spherical coordinates, the equivalent Cartesian routine sla_DTP2V is available.

Starlink User Note 67

P. T. Wallace

12 October 1999

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