Unavoidable drift

Hi there,
I’ve noticed something slightly odd with Mocha AE. I’ve always found it to be very good but the biggest problem for me, as with any tracker really, has been drift.
I’ve noticed that if you track a sequence if entirely identical images, mocha still drifts! Does anyone know how/why this is possible? Does Mocha always drift around in an attempt to find the best matching frame?
Thanks
Tim

Image: http://carsmedia.ign.com/cars/image/article/627/627401/street-drifting-in-osaka-20050620041345962.jpg

Image: http://carsmedia.ign.com/cars/image/article/627/627401/street-drifting-in-osaka-20050620041345962.jpg

Hi there,
Thanks for your reply. Just to get this right- Mocha sort of ‘hunts’ for changes in shear and perspective? Is there a specific ‘hunting’ period before it settles down? I have noticed that often the largest errors can occur at the beginning of tracks - is it possible that the tracker is trying to settle in to position or something?
I have had this happen even with 100 % pixels switched on. It’s not a huge problem by any means, and as you say can be countered using adjust track but it is rather curios.
Thanks again

Hi,
Try tracking only rotation, scale, and translation and upping your % of pixels tracked in your settings, because if you have skew and perspective on mocha will search for those options even if they aren’t there and that can cause drift. Also, adjust track will help lock on any slight drifts.
Let us know if that helps you at all.
Cheers,
Mary

It only hunts for those shifts if you tell it to by having those options switched on, if they’re not in the shot, don’t check them on. That’s all I mean.
Now, if you have them checked off and you’re still getting a settling drift, you can try tracking forwards after it’s “settled” and tracking backwards from that point when the forward track is done… BUT I have not come across this drift phenomenon much unless there’s a weird reflection mocha is picking up OR I am looking for skew and perspective that isn’t happening in the shot.

That means you probably don’t have a large enough image or you have too much compression. It shouldn’t drift if the image isn’t changing.
I’d need to see an example. BUt too much JPEG compression and too small shapes will drift.

That means you probably don’t have a large enough image or you have too much compression. It shouldn’t drift if the image isn’t changing.

I’d need to see an example. BUt too much JPEG compression and too small shapes will drift.