TIC_ONE

       Determine the position of the first tic mark for astronomical images.

       For use in labelling images with right ascension
       and declination axes. This routine determines the
       position in pixels of the first tic.

       tic_one, zmin, pixx, incr, min2, tic1, [RA = ]

       zmin  - astronomical coordinate value at axis zero point (degrees
               or hours)
       pixx - distance in pixels between tic marks (usually obtained from TICS)
       incr - increment in minutes for labels (usually an even number obtained
               from the procedure TICS)

       min2 - astronomical coordinate value at first tic mark
       tic1 - position in pixels of first tic mark

       Suppose a declination axis has a value of 30.2345 degrees at its
       zero point.  A tic mark is desired every 10 arc minutes, which
       corresponds to 12.74 pixels.  Then
       IDL> TIC_ONE, 30.2345, 1, 12.74, min2, tic1
       yields values of min2 = 30.333 and tic1 = 5.74, i.e. the first tic
       mark should be labeled 30 deg 20 minutes and be placed at pixel value
       5.74

       by B. Pfarr, 4/15/87
       Converted to IDL V5.0   W. Landsman   September 1997

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