Point Polygon Test

In this sample you will learn how to use the OpenCV function cv.pointPolygonTest.

Sources:

create sequence of points to make a contour

r = 100;
vert = r * bsxfun(@rdivide, [3 4; 2 6; 3 8; 5 8; 6 6; 5 4], [2 3]);

draw them in an image

sz = 4 * [r r];
src = zeros(sz, 'uint8');
src = cv.line(src, vert, circshift(vert,-1,1), 'Color',255, 'Thickness',3);

get the contours

[contours, hierarchy] = cv.findContours(src, 'Mode','Tree', 'Method','Simple');
contours = cellfun(@(C) cat(1,C{:}), contours, 'Uniform',false);
assert(~isempty(contours));

calculate the distances to the contour

[X,Y] = meshgrid(1:sz(2), 1:sz(1));
tic
D = cv.pointPolygonTest(contours{1}, [X(:) Y(:)], 'MeasureDist',true);
toc
D = reshape(D, sz);

Elapsed time is 0.191564 seconds.

depict the distances graphically

R = zeros(sz, 'uint8'); G = R; B = R;
R(D<0) = 255 - abs(D(D<0)*255 / abs(min(D(:))));
B(D>0) = 255 - D(D>0)*255 / abs(max(D(:)));
R(D==0) = 255; G(D==0) = 255; B(D==0) = 255;
out = cat(3, R, G, B);

show results

subplot(211), imshow(src), title('polygon')
subplot(223), imshow(D,[]), title('distance map')
subplot(224), imshow(out), title('inside, outside, on-edge')