Perspective Transform + Crop in iOS with OpenCV

Question

I\'m trying to implement a cropping & perspective correction feature into an upcoming app. Whilst doing research, I came across:

Executing cv::warpPerspective f

Answer 1

I think the point correspondence in getAffineTransform is incorrect.

Check the point coordinates output by box.points(pts);

Why not just use p1 p2 p3 p4 to calculate the transformation?