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.help dtps2c Jun99 "Slalib Package"
.nf
SUBROUTINE slDPSC (XI, ETA, RA, DEC, RAZ1, DECZ1,
: RAZ2, DECZ2, N)
- - - - - - -
D P S C
- - - - - - -
From the tangent plane coordinates of a star of known RA,Dec,
determine the RA,Dec of the tangent point.
(double precision)
Given:
XI,ETA d tangent plane rectangular coordinates
RA,DEC d spherical coordinates
Returned:
RAZ1,DECZ1 d spherical coordinates of tangent point, solution 1
RAZ2,DECZ2 d spherical coordinates of tangent point, solution 2
N i number of solutions:
0 = no solutions returned (note 2)
1 = only the first solution is useful (note 3)
2 = both solutions are useful (note 3)
Notes:
1 The RAZ1 and RAZ2 values are returned in the range 0-2pi.
2 Cases where there is no solution can only arise near the poles.
For example, it is clearly impossible for a star at the pole
itself to have a non-zero XI value, and hence it is
meaningless to ask where the tangent point would have to be
to bring about this combination of XI and DEC.
3 Also near the poles, cases can arise where there are two useful
solutions. The argument N indicates whether the second of the
two solutions returned is useful. N=1 indicates only one useful
solution, the usual case; under these circumstances, the second
solution corresponds to the "over-the-pole" case, and this is
reflected in the values of RAZ2 and DECZ2 which are returned.
4 The DECZ1 and DECZ2 values are returned in the range +/-pi, but
in the usual, non-pole-crossing, case, the range is +/-pi/2.
5 This routine is the spherical equivalent of the routine slDPVC.
Called: slDA2P
P.T.Wallace Starlink 5 June 1995
Copyright (C) 1995 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
.fi
.endhelp
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