What does Mat::checkVector do in OpenCV?

The official OpenCV's doc says:

cv::Mat::checkVector() returns N if the matrix is 1-channel (N x ptdim) or ptdim-channel (1 x N) or (N x 1); negative number otherwise

OpenCV considers some data types equivalent in case of some functions i.e. objectPoints of cv::solvePnP() can be:

• 1xN/Nx1 1-channel cv::Mat
• 3xN/Nx3 3-channel cv::Mat
• std::vector<cv::Point3f>

With checkVector you can make sure that you are passing the correct representation of your data.