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MGH_PNPOLY

MGH_PNPOLY

## Purpose

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

## Calling Sequence

Result = MGH_PNPOLY(XP, YP, X, Y)

## Inputs

XP,YP: Vectors of X, Y positions defining the polygon.
X,Y: X, Y position(s) defining the point(s) to be tested. Can
be vectors.

## Outputs

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
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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.
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## Modification History

Mark Fardal, Nov 1999:
Written as PNPOLY.
Mark Fardal, Jul 2001: