calculating view angle out of an image

I have an image and I need to get the view angle of each ROI.

by saying view angle i mean the angle between the picture eye, the ROI, and the ground plane.

I know the height of the camera, and I know some reference distances across the image.

is there any way to sample a point in the image and get the view angle?

Answer 1

[Matt J]

You have to calibrate the camera and get the 3x4 projection matrix, P, but once you do it should be quite easy:

u=dot( normalize(P(3,1:1:3),'norm')  , normalize(P(1:3,1:3)\[x;y;1],'norm')  );

angle=acosd(u)+90;