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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 $[\,\xi,\eta\,]$ 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.


next up previous
Next: SLA_DTP2V - Tangent Plane to Direction Cosines
Up: SUBPROGRAM SPECIFICATIONS
Previous: SLA_DTF2R - Hour,Min,Sec to Radians

SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk