Include multiple objects in one contour

edit

How would I "union" the contours?

Just insert every points of one contour into the other one.

I made an image with two objects. I got the two contours then used a for loop to add the points in the second contour to the first using .push_back. This did not work and caused the following error: OpenCV Error: Assertion Failed (0 <= i && i < (int)vv.size()) in cv::_InputArray::getMat, file C:\builds\2_4_PackSlave-win64-vc12-shared\opencv\modules\core\src\matrix.cpp, line977. I'm not sure what I'm doing wrong and have been stuck here for days. I'd appreciate anymore advice you can offer.

Can you provide more information ? When exactly are you issuing this error? When calling the push_back() function ?

No, the push_back function seems to work. When I print out the cv::Points in the contour it shows the coordinates from both contours, so they seem to be added together. However, when I attempt to get the convexHull is when the error is caused. This is the code:

vector<Point> hull; convexHull(Mat(contour), hull, false); drawContours(img, hull, 0, Scalar(255), 1, 8, vector<Vec4i>(), 0, Point());

The error occurs on the convexHull line.

Can't you just use contour instead of Mat(contour) in convexHull ? i.e. convexHull(contour, hull, false) Can you also check that the error is not coming from the instruction "Mat(contour)"

Tried convexHull(contour, hull, false); and got a new error: OpenCV Error: Assertion Failed (i < 0) in cv::_InputArray::getMat, file C:\builds\2_4_PackSlave-win64-vc12-shared\opencv\modules\core\src\matrix.cpp, line963.