Name

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PRECESS_XYZ

Purpose

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Precess equatorial geocentric rectangular coordinates.

Calling Sequence

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precess_xyz, x, y, z, equinox1, equinox2

Input/output

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

Input

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

Output

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x,y,z are changed upon return

Notes

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  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

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

History

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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