OpenCV || matchShapes findContours assertion failed

Question

I am trying to match two contours with the matchShapes method but I always get assertion failed. I know this must have something to do with the wrong Mat format but I can't seem to be able to solve it.

The findContours is working very well:

vector<vector<cv::Point> > contours;
cv::findContours(incomingimage,
                 contours, 
                 CV_RETR_EXTERNAL, 
                 CV_CHAIN_APPROX_SIMPLE);

vector<vector<cv::Point> > contourstwo;
cv::findContours(incomingimagetwo,
                 contourstwo, 
                 CV_RETR_EXTERNAL, 
                 CV_CHAIN_APPROX_SIMPLE);

I get good output from these methods but then

matchShapes(Mat(contours), Mat(contourstwo), CV_CONTOURS_MATCH_I3, 0);

returns

OpenCV Error: Assertion failed

I am a bit in the dark here. Any help would be highly appreciated.

Thank you very much.

Answer 1

I'm also beginner at openCV, but I just figure out how to solve this today (after many trial and error). Please try this one

matchShapes(contours[0], contourstwo[0], CV_CONTOURS_MATCH_I3, 0);

Answer 2

The input to matchShapes according to the documentation should be of the type vector<Point> and not vector<vector<Point> >, as is the output of findContours, just iterate over each contour and pass it to matchShapes.