Calculates a contour area

a = cv.contourArea(curve)
a = cv.contourArea(curve, 'OptionName', optionValue, ...)

Input

• curve Input vector of 2D points (contour vertices) stored in numeric array (Nx2/Nx1x2/1xNx2) or cell array of 2-element vectors ({[x,y], ...}).

Output

• a Output area.

Options

• Oriented Oriented area flag. If it is true, the function returns a signed area value, depending on the contour orientation (clockwise or counter-clockwise). Using this feature you can determine orientation of a contour by taking the sign of an area. By default, the parameter is false, which means that the absolute value is returned.

The function computes a contour area. Similarly to cv.moments, the area is computed using the Green formula. Thus, the returned area and the number of non-zero pixels, if you draw the contour using cv.drawContours or cv.fillPoly, can be different. Also, the function will most certainly give a wrong results for contours with self-intersections.

Example

contour = {[0 0], [10 0], [10 10], [5 4]};
area0 = cv.contourArea(contour);
approx = cv.approxPolyDP(contour, 'Epsilon',5, 'Closed',true);
area1 = cv.contourArea(approx);
fprintf('area0 = %.2f\narea1 = %.2f\napprox poly vertices = %d\n', ...
    area0, area1, numel(approx));