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Mark Overmeer
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Math::Polygon::Calc - Simple polygon calculations


   is a Exporter


 my @poly = ( [1,2], [2,4], [5,7], [1, 2] );

 my ($xmin, $ymin, $xmax, $ymax) = polygon_bbox @poly;

 my $area = polygon_area @poly;
 MY $L    = polygon_perimeter @poly;
 if(polygon_is_clockwise @poly) { ... };
 my @rot  = polygon_start_minxy @poly;


This package contains a wide variaty of relatively easy polygon calculations. More complex calculations are put in separate packages.



Returns the area enclosed by the polygon. The last point of the list must be the same as the first to produce a correct result.

The algorithm was found at http://mathworld.wolfram.com/PolygonArea.html, and sounds:

 A = abs( 1/2 * (x1y2-x2y1 + x2y3-x3y2 ...)

Returns a list with four elements: (xmin, ymin, xmax, ymax), which describe the bounding box of the polygon (all points of the polygon are within that area.

polygon_beautify( [$options], LIST-of-$points )

Polygons, certainly after some computations, can have a lot of horrible artifacts: points which are double, spikes, etc. This functions provided by this module beautify The optional HASH contains the $options:

 -Option        --Default
  remove_between  <false>
  remove_spikes   <false>
remove_between => BOOLEAN

Simple points in-between are always removed, but more complex points are not: when the line is not parallel to one of the axes, more intensive calculations must take place. This will only be done when this flags is set. NOT IMPLEMENTED YET

remove_spikes => BOOLEAN

Returns the centroid location of the polygon. The last point of the list must be the same as the first to produce a correct result.

The algorithm was found at http://en.wikipedia.org/wiki/Centroid#Centroid_of_polygon


Be sure the polygon points are in clockwise order.

polygon_contains_point($point, LIST-of-$points)

Returns true if the point is inside the closed polygon. On an edge will be flagged as 'inside'. But be warned of rounding issues, caused by the floating-point calculations used by this algorithm.


Be sure the polygon points are in counter-clockwise order.

polygon_distance($point, @polygon)

[1.05] calculate the shortest distance between a point and any vertex of a closed polygon.

polygon_equal( ARRAY-of-$points, ARRAY-of-$points, [$tolerance] )

Compare two polygons, on the level of points. When the polygons are the same but rotated, this will return false. See polygon_same().


The length of the line of the polygon. This can also be used to compute the length of any line: of the last point is not equal to the first, then a line is presumed; for a polygon they must match.

This is simply Pythagoras.

 $l = sqrt((x1-x0)^2 + (y1-y0)^2) + sqrt((x2-x1)^2+(y2-y1)^2) + ...
polygon_same( ARRAY-of-$points, ARRAY-of-$points, [$tolerance] )

Compare two polygons, where the polygons may be rotated wrt each other. This is (much) slower than polygon_equal(), but some algorithms will cause un unpredictable rotation in the result.


Returns the polygon, where the point which is closest to the left-bottom corner of the bounding box is made first.



This module is part of Math-Polygon distribution version 1.06, built on July 16, 2017. Website: http://perl.overmeer.net/geo/


Copyrights 2004-2017 by [Mark Overmeer]. For other contributors see ChangeLog.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See http://dev.perl.org/licenses/