Camschnapper and Principal Points

General TouchDesigner Discussion
1

Does a Camschnapper solution calculate the ‘principal point’ of image? In this case - basically every projection situation encountered these days - an offset in the principal point would equate to a lens shift.

This seems to indicate yes:

r = tdu.calibrateCamera((geoPoints,imgPoints),width=pWidth, height=pHeight, fov=80, useIntrinsicGuess=True, fixAspectRatio=True, zeroTangentDist=True, fixPrincipalPoint=False)

Ah ha - there are the resultant principal points… and they seem to make a bit of sense… if in pixels. So, my lens shifted up (bottom of screen) projector has 2560 x 1440 res (for some reason) and shows principalX as 925 (I’d expect 1280, but that seems in range) and 1424, which makes sense.

So - where do those values go? Do they end up in the matrix?

Follow-up - I’m trying to visualize the projection frustum. I put a simple box (3D parented to camera/projector), and applied the matrix, and get something. But it’s pretty odd - physically shifted down and off aspect. Has anyone done this already? I’m thinking there’s a formula.

I know other people want this - be good to add it to camschnapper when it works.

Bruce

2

To visualize the frustum in world space multiply the inverse of the projection matrix by the points in the unit cube going from (-1, -1, -1) to (1, 1, 1). This will give you a frustum with one side of the shape at the near plane and one at the far plane.

3

Great, I’ll try that, thanks.