I want to show a video over a user-defined target. The video must "fit" inside a rectangle that is presented to the user as a 2D GUI.
So if say, I have a GUI rectangle that is a third of the height of the device's screen height, what scale should be the 3D plane containing the video? So that the video appears "inside" the GUI rectangle? (of course only in the original state where the user is supposed to be parallel to the target)
Is there a formula? Should I try to find a relationship with CameraCalibration.getSize() ? Or CameraCalibration.getPrincipalPoint () ?