/usr/share/octave/packages/geometry-1.7.0/polygons2d/polygonArea.m is in octave-geometry 1.7.0-1build1.
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## Copyright (C) 2004-2011 INRA - CEPIA Nantes - MIAJ (Jouy-en-Josas)
## Copyright (C) 2012 Adapted to Octave by Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
## All rights reserved.
##
## Redistribution and use in source and binary forms, with or without
## modification, are permitted provided that the following conditions are met:
##
## 1 Redistributions of source code must retain the above copyright notice,
## this list of conditions and the following disclaimer.
## 2 Redistributions in binary form must reproduce the above copyright
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##
## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ''AS IS''
## AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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## -*- texinfo -*-
## @deftypefn {Function File} {@var{area} = } polygonArea (@var{points})
## @deftypefnx {Function File} {@var{area} = } polygonArea (@var{px},@var{py})
## Compute the signed area of a polygon.
##
## Compute area of a polygon defined by @var{points}. @var{points} is a N-by-2
## matrix containing coordinates of vertices.
##
## Vertices of the polygon are supposed to be oriented Counter-Clockwise
## (CCW). In this case, the signed area is positive.
## If vertices are oriented Clockwise (CW), the signed area is negative.
##
## If polygon is self-crossing, the result is undefined.
##
## If @var{points} is a cell, each element is considered a polygon and the area
## of each one is returned in the matrix @var{area}. The matrix has the same shape
## as the cell.
##
## References:
## Algorithm adapted from P. Bourke web page
## http://local.wasp.uwa.edu.au/~pbourke/geometry/polyarea/
##
## @seealso{polygons2d, polygonCentroid, drawPolygon}
## @end deftypefn
function area = polygonArea(varargin)
var = varargin{1};
# in case of polygon sets, computes several areas
if iscell (var)
area = cellfun (@func, var);
# area = zeros(length(var), 1);
# for i = 1:length(var)
# area(i) = polygonArea(var{i}, varargin{2:end});
# end
# return;
# end
else
# extract coordinates
if nargin == 1
area = func(var)
elseif nargin == 2
px = varargin{1};
py = varargin{2};
# indices of next vertices
N = length(px);
iNext = [2:N 1];
# compute area (vectorized version)
area = sum(px .* py(iNext) - px(iNext) .* py) / 2;
end
end
endfunction
function a = func (c)
N = length (c);
iNext = [2:N 1];
a = sum (c(:,1) .* c(iNext,2) - c(iNext,1) .* c(:,2)) / 2;
endfunction
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