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PRECESS_XYZ

PRECESS_XYZ

Name


PRECESS_XYZ

Purpose


Precess equatorial geocentric rectangular coordinates.

Calling Sequence


precess_xyz, x, y, z, equinox1, equinox2

Input/output


x,y,z: scalars or vectors giving heliocentric rectangular coordinates
              THESE ARE CHANGED UPON RETURNING.

Input


EQUINOX1: equinox of input coordinates, numeric scalar
      EQUINOX2: equinox of output coordinates, numeric scalar

Output


x,y,z are changed upon return

Notes


  The equatorial geocentric rectangular coords are converted
      to RA and Dec, precessed in the normal way, then changed
      back to x, y and z using unit vectors.

Example


Precess 1950 equinox coords x, y and z to 2000.
IDL> precess_xyz,x,y,z, 1950, 2000

History


Written by P. Plait/ACC March 24 1999
(unit vectors provided by D. Lindler)
      Use /Radian call to PRECESS W. Landsman November 2000
      Use two parameter call to ATAN W. Landsman June 2001



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