Hi folks, I'd be keen to hear some feedback from users on a couple of regular issues in using iPi. It would be good to get an understanding of how others cope in these situations.

Situation 1.

At point 1. leg tracking is fine.
At point 2, the tracking has been lost.
So you go to point 3, where the software can track the leg again and you track backwards. You track backwards from point 3, to about point 2 and the tracking is ok, and so now in theory you have good tracking throughout the whole motion.

Except, theres a jump, because the tracking backwards doesn't quite match the first pass, where you tracked forwards. What do you do? Its like the second pass needs markers to instruct 100% influence at the beginning of reverse tracking, and 0% influence once its passed the 2nd point, where tracking was originally lost (thus allowing the forst pass to have 100% influence).

Anyways, what are peoples tips to smooth out the two tracking sessions where they meet?

Thanks a bunch
AaronC

It's a little difficult to nail down a workflow because different motions may require novel combinations of techniques.

That said, many common tracking errors can be fixed predictably.

When I get a tracking error, say a leg or arm starts to 'flip out', in many cases I can copy the last good limb pose, paste the limb pose throughout the ROI where the error occurs, go to the last frame of the ROI, click Refit Pose, and then Track Backwards through the ROI. Alternatively, I might correct the last frame of the ROI, click Refit Pose, copy and paste that throughout the ROI, and then Track Backwards through the error. This method usually works well. If I still see some bumps, I run a Refine pass through the error ROI, usually backwards.

Don't worry if the motion is jittering--that can be cleaned up later using Jitter Removal. When tracking, focus on smoothing the bigger 'bumps' in motion. You can tell normal 'jitter' from a 'bump' by enabling show Trajectory--'jitter' is constant and 'bumps' are the big spikes in the path. Pay attention to the big spikes that break from the general motion curve--often times, running Track Backwards through the spike will clean it up. If that doesn't work, manually adjust it and click Refit Pose. If Refit Pose happens to make the fit worse instead of better, simply undo the action.

Note 1: if you have head motion that looks good, disable head tracking so it doesn't get re-tracked. This can save processing time.

Note 2: if you use different Jitter Removal settings throughout the motion, remember to 'touch' the Trajectory Filter (i.e., bump the setting to another value and back.) This smooth the transitions between Jitter Removal settings.

Note 3: Jitter Removal is not additive--when you use it, it resets to the tracked motion within the ROI, so you can experiment freely with different settings without worrying about it messing up your tracking results.

I just worked on a motion that has some typical errors and I was thinking it would make a good candidate for a tutorial video. I'll post a general tracking error correction workflow video as soon as I can make time.

G.

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That would be outstanding. Thanks for your feedback, I was hoping you'd chime in!

~A