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MGH_PNPOLY

MGH_PNPOLY

Name


  MGH_PNPOLY

Purpose


  Determine whether a point or set of points is inside a polygon.

Calling Sequence


  result = mgh_pnpoly(x, y, xp, yp)
  result = mgh_pnpoly(x, y, xyp)

Positional Parameters


  x, y (input, numeric scalar or array
    X, Y position(s) defining the point(s) to be tested.
  xp, yp (input, numeric vector)
  xyp (input, numeric array)
    The polygon vertices as 2 separate vectors (xp, yp) OR a single
    [2,n] array.

Return Value


  The function returns an array of the same shape as X. Each element
  is 0 if the point is outside the polygon, 1 if it is inside the
  polygon. The comp.graphics.algorithms has the following to say
  about points on the boundary:
      "It returns 1 for strictly interior points, 0 for strictly
      exterior, and 0 or 1 for points on the boundary. The boundary
      behavior is complex but determined; in particular, for a
      partition of a region into polygons, each point is "in"
      exactly one polygon. (See p.243 of [O'Rourke (C)] for a
      discussion of boundary behavior.)"

Procedure


  Ray-crossing technique of WR Franklin from
  Comp.graphics.algorithms FAQ.

References


    - "Misc Notes - WR Franklin",
      http://www.ecse.rpi.edu/Homepages/wrf/misc.html: includes a
      reference (broken @ Jul 2001) to his point-in-polygon code.
    - Comp.graphics.algorithms FAQ,
      http://www.faqs.org/faqs/graphics/algorithms-faq/: See subject
      2.03
###########################################################################
  Copyright (c) 1999-2015 NIWA:
  http://www.niwa.co.nz/
  Licensed under the MIT open source license:
  http://www.opensource.org/licenses/mit-license.php
###########################################################################

Modification History


  Mark Fardal, 1999-11:
    Written as PNPOLY.
  Mark Fardal, 2001-07:
    Added header.
  Mark Hadfield, 2001-07:
    Renamed MGH_PNPOLY. Output now matches input in shape, not just
    size.
  Mark Hadfield, 2009-09:
    - Changed order of parameters: points to be tested come before
      polygon.
    - Polygon can now be specified as a [2,n] array.



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