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MGH_POLYCLIP

MGH_POLYCLIP

Name


  MGH_POLYCLIP

Purpose


  Clip an arbitrary polygon on the X-Y plane to a line parallel
  to the X or Y axis using the Sutherland-Hodgman algorithm.
 

Category


  Graphics, Region of Interest, Geometry

Calling Sequence


  result = MGH_POLYCLIP(poly, clip, dir, neg, COUNT=count)

Return Value


  The function returns the clipped polygon as a [2,n] array. The
  second dimension will equal the value of the COUNT argument, except
  where COUNT is 0 in which case the return value is -1.
  POSITIONAL ARGUMENTS
  poly (input, floating array)
    A [2,m] vector defining the polygon to be clipped.
  cval (input, numeric sclar)
    The value of X or Y at which clipping is to occur
  dir (input, integer scalar)
    Specifies whether clipping value is an X (dir = 0) or Y (dir =
    1) value.
  neg (input, integer scalar)
    Set this argument to 1 to clip to the negtive side, 0 to clip to
    the positive side.

Keyword Parameters


  COUNT (output, integer)
    The number of vertices in the clipped polygon.

Procedure


  The polygon is clipped using the Sutherland-Hodgman algorithm.
  This function is based on JD Smith's implementation of the
  Sutherland-Hodgman algorithm in his POLYCLIP function. He can
  take all of the credit and none of the blame.
###########################################################################
  Copyright (c) 2001-2013 NIWA:
  http://www.niwa.co.nz/
  Licensed under the MIT open source license:
  http://www.opensource.org/licenses/mit-license.php
###########################################################################

Modification History


  Mark Hadfield, 2001-10:
    Written, based on JD Smith's POLYClIP.
  Mark Hadfield, 2013-06:
    - The result array is now allocated before looping through the input
      vertices, wherease before it was progressively built up by concatenation.
      This change results in an enormous speed-up for large (> 10,000) polygons.
    - Order of positional arguments changed (poly is now first) to match
      MGH_POLYCLIP2.



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