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 tangent plane rectangular coordinates (radians)

RAZ,DECZ D spherical coordinates of tangent point (radians)

RETURNED:

RA,DEC 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_DTP2V is available.