We then need to put the 2D image points in another vector. Remember that they must be put in the array in the same order that the model points were inserted in; this way, the i'th 2D image point matches the i'th 3D model point. A catch here is that the origin for the 2D image points is located at the center of the image, which might require you to translate them. You can insert the following 2D image points (of course, they will vary according to the user's matching):