SLA_DTP2S

Tangent Plane to Spherical

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 [ξ, η] 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_DTP2V is available.