wolffd@0: function  a = polygon_area(x,y)
wolffd@0: % AREA  Area of a planar polygon.
wolffd@0: %	AREA(X,Y) Calculates the area of a 2-dimensional
wolffd@0: %	polygon formed by vertices with coordinate vectors
wolffd@0: %	X and Y. The result is direction-sensitive: the
wolffd@0: %	area is positive if the bounding contour is counter-
wolffd@0: %	clockwise and negative if it is clockwise.
wolffd@0: %
wolffd@0: %	See also TRAPZ.
wolffd@0: 
wolffd@0: %  Copyright (c) 1995 by Kirill K. Pankratov,
wolffd@0: %	kirill@plume.mit.edu.
wolffd@0: %	04/20/94, 05/20/95  
wolffd@0: 
wolffd@0:  % Make polygon closed .............
wolffd@0: x = [x(:); x(1)];
wolffd@0: y = [y(:); y(1)];
wolffd@0: 
wolffd@0:  % Calculate contour integral Int -y*dx  (same as Int x*dy).
wolffd@0: lx = length(x);
wolffd@0: a = -(x(2:lx)-x(1:lx-1))'*(y(1:lx-1)+y(2:lx))/2;
wolffd@0: a = abs(a);