.help v2tp Jun99 "Slalib Package"
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      SUBROUTINE slV2TP (V, V0, XI, ETA, J)

     - - - - -
      V 2 T P
     - - - - -

  Given the direction cosines of a star and of the tangent point,
  determine the star's tangent-plane coordinates.

  (single precision)

  Given:
     V         r(3)    direction cosines of star
     V0        r(3)    direction cosines of tangent point

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

  Notes:

  1  If vector V0 is not of unit length, or if vector V is of zero
     length, the results will be wrong.

  2  If V0 points at a pole, the returned XI,ETA will be based on the
     arbitrary assumption that the RA of the tangent point is zero.

  3  This routine is the Cartesian equivalent of the routine slS2TP.

  P.T.Wallace   Starlink   27 November 1996

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

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