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      Make a monochrome shaded relief view of a surface.


Calling Sequence

      t = topo(z, az, ax)


      z = array of elevations to shade. in
      az = light source angle from zenith in deg (def = 45). in
      ax = light source angle from x axis in deg (def = 45). in

Keyword Parameters


        DELTA=d Set a range of slopes in degrees to map to 0 to 1.
          Delta is relative to sun angle. Try small value, 5 or 10.
        ZERO=v Value (0 to 1) to map zero slope (flat surface) to.
          May be used with DELTA (DELTA=10 if not given with ZERO).


Common Blocks


      Note: there are no true shadows. DELTA and ZERO give better
        control over brightness and avoid low sun angles returning
        low brightness results. The operation of DELTA and ZERO
        are roughly: ZERO is brightness, DELTA is contrast.
        Best values depend on the data but ZERO=.5 and DELTA
        around 5 to 15 might be reasonable.

Modification History

      R. Sterner. 19 Nov, 1987.
      R. Sterner, 27 Jan, 1993 --- dropped reference to array.
      R. Sterner, 1994 Jun 6 --- Made a minor memory savings.
      R. Sterner, 1994 Jun 28 --- Added DELTA and ZERO keywords.
      R. Sterner, 2010 May 23 --- Converted arrays from () to [].
      Johns Hopkins University Applied Physics Laboratory.
  Copyright (C) 1987, Johns Hopkins University/Applied Physics Laboratory
  This software may be used, copied, or redistributed as long as it is not
  sold and this copyright notice is reproduced on each copy made. This
  routine is provided as is without any express or implied warranties
  whatsoever. Other limitations apply as described in the file disclaimer.txt.

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