Tracking drift issues

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Since being able to track a longer frame sequence, I'm finding that over time there is drift in the feature tracked location. An example of this is in the video below:

It may be hard to see in the video (watching it in full-screen may or may not help..!), but at around frame 100 the location of the marker begins to move away. It started in the middle of a darker area on the van's graphics. But it ends up in a lighter grey area. This area doesn't really have much track value, and the tracking eventually fails. Below is an image of the starting and finishing track positions, visualised in the selected feature tracking window.

Tracking drift visualised
Tracking drift visualised: on the left is the starting position, and on the right the failed finished position frame 209.

Tracking drift occurs when the tracking error builds up over time. The system can't get a 100% track each frame, so over time an accumulation of errors can result in a feature marker moving off its original target over a large sequence. These drifting markers will lead to poor looking track results. Most importantly, it will affect the camera pose estimation and throw off the final rendered animation. While one might get away with small differences, in more critical places the finished product could look poorly produced. Either way, it is still an issue I think we should address.

Now, we can address this by manually going back and fixing the frames where the drift starts to happen. Good tracking is done by an artist who is willing to do the leg work to get the best results. Ultimately, for best results, I think manual tracking is part of the toolkit. And I'm for it.

However, I have a few things that I think can help the drifting. And if this in turn helps reduce the manual workload, then that should be seen as a good thing, particularly when it comes to the time component of a track job.

More to unravel on this one.