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TICPOS

TICPOS

Name


      TICPOS

Purpose


      Specify distance between tic marks for astronomical coordinate overlays

Explanation


      User inputs number an approximate distance
      between tic marks, and the axis length in degrees. TICPOS will return
      a distance between tic marks such that the separation is a round
      multiple in arc seconds, arc minutes, or degrees

Calling Sequence


      TICPOS, deglen, pixlen, ticsize, incr, units

Inputs


      deglen - length of axis in DEGREES
      pixlen - length of axis in plotting units (pixels)
      ticsize - distance between tic marks (pixels). This value will be
              adjusted by TICPOS such that the distance corresponds to
              a round multiple in the astronomical coordinate.

Outputs


      ticsize - distance between tic marks (pixels), positive scalar
      incr - incremental value for tic marks in round units given
              by the UNITS parameter
      units - string giving units of ticsize, either 'ARC SECONDS',
              'ARC MINUTES', or 'DEGREES'

Example


      Suppose a 512 x 512 image array corresponds to 0.2 x 0.2 degrees on
      the sky. A tic mark is desired in round angular units, approximately
      every 75 pixels.
      IDL> ticsize = 75
      IDL> TICPOS,0.2,512,ticsize,incr,units
      ==> ticsize = 85.333, incr = 2. units = 'Arc Minutes'
      i.e. a good tic mark spacing is every 2 arc minutes, corresponding
      to 85.333 pixels.

Revison History


      written by W. Landsman November, 1988
      Converted to IDL V5.0 W. Landsman September 1997
      Don't use all capital letters W. Landsman May 2003
      Fix case where incr crosses degree/minute or minute/degree boundary
              A. Mortier/W.Landsman April 2005



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