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From: Ivo Petkovi? on 28 May 2010 10:37
"Bruno Luong" <b.luong(a)fogale.findmycountry> wrote in message <ht1pcm$c74$1(a)fred.mathworks.com>...
> I have take a pain to code it, LOL. I also take opportunity to improve my poly2poly() function for speed. Here we go:
>
> function b = isintersect(P1, P2)
> % function b = isintersect(P1, P2)
> % Check if two polygons intersect
>
> c = poly2poly(P1, P2);
> if isempty(c)
> b = inpolygon(P2(1,1),P2(2,1),P1(1,:),P1(2,:)) || ...
> inpolygon(P1(1,1),P1(2,1),P2(1,:),P2(2,:));
> else
> b = true;
> end
>
> end % isintersect
>
> function c = poly2poly(P1, P2)
> % function c = poly2poly(P1, P2)
> % intersection of two polygons P1 and P2.
> % P1 and P2 are two-row arrays, each column is a vertice
> % c is also two-row arrays, each column is an intersecting point
>
> % Pad the first point to the end if necessary
> if ~isequal(P1(:,1),P1(:,end))
> P1 = [P1 P1(:,1)];
> end
> if ~isequal(P2(:,1),P2(:,end))
> P2 = [P2 P2(:,1)];
> end
>
> c = zeros(2,0);
> for n=2:size(P1,2)
> c=[c seg2poly(P1(:,n-1:n), P2)]; %#ok
> end
>
> end % poly2poly
>
> function c = seg2poly(s1, P)
> % function c = seg2poly(s1, P)
> % Check if a segment (2 x 2) segment s1 intersects with a polygon P.
> % s(:,1) is the first point s(:,2) is the the second point of the segment.
> % P is (2 x n) arrays, each column is a vertices
>
> % Translate and rotation so that first point is origin
> % the second point is on y-axis
> a = s1(:,1);
> M = bsxfun(@minus, P, a);
> b = s1(:,2)-a;
> nb2 = b(1)^2+b(2)^2;
> R = [b(2) -b(1);
> b(1) b(2)];
> M = R*M;
> sx = sign(M(1,:));
> % x -coordinates has opposite signs
> ind = sx(1:end-1).*sx(2:end) <= 0;
> if any(ind)
> ind = find(ind);
> % cross point to y-axis
> x1 = M(1,ind);
> x2 = M(1,ind+1);
> y1 = M(2,ind);
> y2 = M(2,ind+1);
> dx = x2-x1;
> y = (y1.*x2-y2.*x1)./dx;
> y = y/nb2;
> ind = y>=0 & y<1;
> if any(ind)
> c = bsxfun(@plus, b*y(ind), a);
> else
> c = zeros(2,0);
> end
> else
> c = zeros(2,0);
> end
>
> end % seg2poly
>
> % Bruno

I will try it now. Thanks man!
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