SLA_TP2S - Tangent Plane to Spherical

ACTION:

Transform tangent plane coordinates into spherical coordinates (single precision)

CALL:

CALL sla_TP2S (XI, ETA, RAZ, DECZ, RA, DEC)

GIVEN:

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

RETURNED:

RA,DEC

R

spherical coordinates (radians)

NOTES:

1. The projection is called the gnomonic projection; the Cartesian coordinates $[ \xi,\eta ]$ 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 $[ x,y,z ]$ rather than spherical coordinates, the equivalent Cartesian routine sla_TP2V is available.