Track is fine, then add keyframes, makes shapes go funky

Hi, I just got done with a hard deadline, two week mocha 4 project. This problem happened enough for me to want to find the solution here. While I was doing the project, I just had to redo the roto, which was a pain.

Project: Making shapes on a car for a color change

Problem: I would have a perfectly fine track, and then start adjusting areas of shape mask (I first use one layer to track, then link my shape mask to tracked layer) Everything would be fine. Then as I added a keyframe all of sudden between it and the last keyframe the track would go funky. As I frame by frame everything is okay. Keep moving frame by fraem, it would be good, good, and then distort randomly. Points would go everywhere, shape looks like a two year old learned how to draw right angles, then a couple of frames later return to normal. I don’t have any of the project I can reference. But if it happens to me ever again I can show you.

I was just wondering if anyone knows about this?

Yes, this sounds like the problem where mocha can’t tolerate the planar surface moving behind the camera.

If you are using perspective when you track, it may be that your surface is going behind the camera in mocha and corrupting the data. In mocha, problem splines can occur when the tracking data has become so skewed it goes off or “behind” camera, the keyframes the tracking data generates can throw the shape information out of order. You may need to re-track the shape using only translation, scale, rotation, and shear instead of perspective. This is especially true for complex roto of an object that is turning away from screen or tracking an object that is turning.

I don’t use perspective at all when I roto, because roto has to track everything, not just sections in the shot that were planned for tracking.

Okay, I just got some example pictures I can email.