Problem with The Foundary’s Camera Tracker for AE *Z-axis*

[Tim Parsons]

OK, I’m a dork… I affirmed that it worked, but I had forgoten to switch on motion blur, which is what illuminated this problem to begin with… And it was still spinning! I can’t for the life of me figure out why!

Here’s the 3-frame progression of the problem with the original z-rotation values.

-179.93

-179.9626

179.9956.

The z-rotation values were changed because of the expression, but the image didn’t respond! It was as if the expression weren’t even there, even though the final numbers were correct.

So then I tried “Convert Expression to Keyframes” and it works wonderfully (I double-checked this time).

Why?! Grr!

[Cassius Marques]

Damn it! haha. I guess it can only be because AE can do subframe calculations(for motion blur reasons), and between frame 231 and 232 there are still negative values. Once it hits 232 and the expressions kicks in, values change for positive but with still subframe negative values. Expressions must only affect full frames and not for the n*samples subframes generated for the motion blur computation.

That’s my best guess.

[Cassius Marques]

And just to elucidate, earlier in the morning (here in Brazil) you asked but I didn’t had the time to figure out a proper answer to why it happens, so now I’ll try and here it goes. Check this image. It shows the expected behaviour of a real camera. Once you hit that 180º angle on the y axis, you gotta turn the camera around otherwise the whole world would turn upside down.

Perhaps the underlying math in the plugin doesn’t account the fact that we would interpolate frames, or perhaps it does but it chose that “optimal” solution because of some other expcted behaviour that we would never predict.