Fellas, I'm trying to 3d model a vehicle (hobby of mine). Documentation is basically non-existant apart from general dimensions. What I'm trying to do is recover the position of the cannon's trunnions (the axis on which the gun points upwards/downwards). I know it can go a maximum of +20/-10 degrees.

So, I'm thinking on how to recover information from pictures like (pic related).

Assume XY for vehicle length/width, Z for height. Am I correct to assume that I can infer the Z rotation of the vehicle by just taking the proportion between the 19/26 degrees angles? That is, if the vehicle was rotated 45º on Z , I'd have 45/45 looking from above, going to 0/0 when parallel to the ground. If it was 30 degrees, would I always have a 1/3 : 2/3 ratio?

I don't have the camera info (though it doesn't look too distorted, not sure it influences much at all).

Anyways, open to ideas.