wolffd@0: function [is,S] = isintpl(x1,y1,x2,y2)
wolffd@0: % ISINTPL Check for intersection of polygons.
wolffd@0: %	[IS,S] = ISINTPL(X1,Y1,X2,Y2) Accepts coordinates
wolffd@0: %	X1,Y1 and X2, Y2 of two polygons. Returns scalar
wolffd@0: %	IS equal to 1 if these polygons intersect each other
wolffd@0: %	and 0 if they do not.
wolffd@0: %	Also returns Boolean matrix S of the size length(X1)
wolffd@0: %	by length(X2) so that {ij} element of which is 1 if 
wolffd@0: %	line segments i to i+1 of the first polygon and 
wolffd@0: %	j to j+1 of the second polygon intersect each other,
wolffd@0: %	0 if they don't and .5 if they "touch" each other.
wolffd@0: 
wolffd@0: %  Copyright (c) 1995 by Kirill K. Pankratov,
wolffd@0: %       kirill@plume.mit.edu.
wolffd@0: %       06/20/95, 08/25/95
wolffd@0: 
wolffd@0: 
wolffd@0:  % Handle input ...................................
wolffd@0: if nargin==0, help isintpl, return, end
wolffd@0: if nargin<4
wolffd@0:   error(' Not enough input arguments ')
wolffd@0: end
wolffd@0: 
wolffd@0:  % Make column vectors and check sizes ............
wolffd@0: x1 = x1(:); y1 = y1(:);
wolffd@0: x2 = x2(:); y2 = y2(:);
wolffd@0: l1 = length(x1);
wolffd@0: l2 = length(x2);
wolffd@0: if length(y1)~=l1 | length(y2)~=l2
wolffd@0:   error('(X1,Y1) and (X2,Y2) must pair-wise have the same length.')
wolffd@0: end
wolffd@0: 
wolffd@0:  % Quick exit if empty
wolffd@0: if l1<1 | l2<1, is = []; S = []; return, end
wolffd@0: 
wolffd@0:  % Check if their ranges are intersecting .........
wolffd@0: lim1 = [min(x1) max(x1)]';
wolffd@0: lim2 = [min(x2) max(x2)]';
wolffd@0: isx = interval(lim1,lim2);  % X-ranges
wolffd@0: lim1 = [min(y1) max(y1)]';
wolffd@0: lim2 = [min(y2) max(y2)]';
wolffd@0: isy = interval(lim1,lim2);  % Y-ranges
wolffd@0: is = isx & isy;
wolffd@0: S = zeros(l2,l1);
wolffd@0: 
wolffd@0: if ~is, return, end  % Early exit if disparate limits
wolffd@0: 
wolffd@0:  % Indexing .......................................
wolffd@0: [i11,i12] = meshgrid(1:l1,1:l2);
wolffd@0: [i21,i22] = meshgrid([2:l1 1],[2:l2 1]);
wolffd@0: i11 = i11(:); i12 = i12(:);
wolffd@0: i21 = i21(:); i22 = i22(:);
wolffd@0: 
wolffd@0:  % Calculate matrix of intersections ..............
wolffd@0: S(:) = iscross([x1(i11) x1(i21)]',[y1(i11) y1(i21)]',...
wolffd@0:                [x2(i12) x2(i22)]',[y2(i12) y2(i22)]')';
wolffd@0: 
wolffd@0: S = S';
wolffd@0: is  = any(any(S));
wolffd@0: