Here is an exercise for sightseers. Choose a famous photo that was taken at a recognizable location, somewhere that should still look similar today. Travel to that site and explore it until you know how the photographer set up the shot. Where was the camera positioned and how was it rotated?

If you found an answer, and if you are sure of it, you must have already known which lens (and, for a zoom lens, which zoom setting) the photographer used. Without this information, you could not have narrowed down the feasible camera poses to the one true pose.

We face a similar problem when trying to determine the pose of a photographed object relative to a monocular (single-lens) camera. To find a unique solution, we first need to know the camera's horizontal and vertical field of view, and horizontal and vertical resolution in pixels.

Fortunately, we can get this data via the android.hardware.Camera.Parameters class. Our CameraProjectionAdapter...