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      SUBROUTINE slDSTP (RA, DEC, RAZ, DECZ, XI, ETA, J)

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      D S T P
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  Projection of spherical coordinates onto tangent plane:
  "gnomonic" projection - "standard coordinates" (double precision)

  Given:
     RA,DEC      dp   spherical coordinates of point to be projected
     RAZ,DECZ    dp   spherical coordinates of tangent point

  Returned:
     XI,ETA      dp   rectangular coordinates on tangent plane
     J           int  status:   0 = OK, star on tangent plane
                                1 = error, star too far from axis
                                2 = error, antistar on tangent plane
                                3 = error, antistar too far from axis

  P.T.Wallace   Starlink   18 July 1996

  Copyright (C) 1996 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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