Name

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  MGH_POLYCLIP2

Purpose

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  Clip an arbitrary polygon on the X-Y plane to a line of arbitrary
  orientation using the Sutherland-Hodgman algorithm.

Category

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  Graphics, Region of Interest, Geometry

Calling Sequence

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  result = MGH_POLYCLIP2(clip, poly, COUNT=count)

Positional Parameters

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  poly (input, floating array)
    A [2,m] vector defining the polygon to be clipped.
  clip (input, 3-element numeric vector)
    This parameter describes the line to be clipped to. The polygon is
    clipped to the half-plane (clip[0] x + clip[1] y + clip[2]) < 0.

Keyword Parameters

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

Return Value

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  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.

Procedure

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  The polygon is clipped using the Sutherland-Hodgman algorithm.
  This function is similar to MGH_POLYCLIP, which was written first
  & clips to vertical or horizontal lines only. It turns out that
  MGH_POLYCLIP2 is competitive with MGH_POLYCLIP in terms of speed
  so the former may supersede the latter.
  Both polygon-clipping functions are based on JD Smith's
  implementation of the Sutherland-Hodgman algorithm in his POLYCLIP
  function. He can take most of the credit and none of the blame.
###########################################################################
  This software is provided subject to the following conditions:
  1. NIWA makes no representations or warranties regarding the
    accuracy of the software, the use to which the software may
    be put or the results to be obtained from the use of the
    software. Accordingly NIWA accepts no liability for any loss
    or damage (whether direct of indirect) incurred by any person
    through the use of or reliance on the software.
  2. NIWA is to be acknowledged as the original author of the
    software where the software is used or presented in any form.
###########################################################################

Modification History

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  Mark Hadfield, 2002-08:
    Written.