Foot Slide

Ursine · **Joined:** Thu Jun 30, 2011 5:45 am **Posts:** 3

I'm a long time Vicon mocap user and I'm intrigued with the quality you can acheive with a markerless system with a half dozen inexpensive cameras. One issue that I keep seeing with the system is foot slide. Is this a calibration or camera placement issue? I know I can clean up in Motionbuilder, but I prefer not to have to.

Dave

Greenlaw · **Posted:** Thu Jun 30, 2011 9:23 pm

With the six camera PS3 Eye setup, feet sliding really isn't an issue if you have proper calibration and clean motion data. One problem I've seen is that the legs do not rotate around 'Y' much at the hips which can cause feet to rotate with the hips in certain 'twisting' positions. The video I posted a year ago illustrates this. On the bright side, this problem occurs rarely and it can be fixed easily in Motion Builder. I really haven't noticed it at all during walks, even when walking into turns.

What I really want now is head tracking. It's easy enough to add head motion in post, but right now I'm dealing with footage where head tracking could have been very useful: I have a character playing a harmonica and I'm trying to use Motion Builder's IK Constraint to keep the character's lips stuck to the instrument. But I'm having trouble making the IK work fulltime so I'll probably wind up rigging the IK Constraint in my main 3D program instead of Motion Builder.

For the most part, the iPi data has been surprisingly good for an entry level markerless system. Upon close inspection, the data can be a little 'shakier' than the high-end mocap we normally deal with at work, but in many cases it looks pretty solid. For many professional users it's excellent for previs and background characters, and within reason you could probably make it work for final quality motions. (Just don't expect to make the next Avatar with it.)

For me personally, iPi DMC has been the perfect system for the short film project my wife and I are working on, and it capabilities have grown way beyond what I originally expected from it over two years ago. :)

G.

Michael Nikonov · **Joined:** Tue Mar 31, 2009 9:13 pm **Posts:** 805

Can you please provide more details about foot sliding that you see. Do you use Jitter Removal filter?

Current version of our software lacks certain degrees of freedom for foot sideway motion. Therefore some foot sliding is unavoidable for a motion like this (0:17-0:23): http://www.youtube.com/watch?v=G2KLtGsl-L0

For other types of motions there should not be foot sliding. If you see foot sliding in different scenario then we would be very interested to know more details because this can be a bug.

Ursine · **Joined:** Thu Jun 30, 2011 5:45 am **Posts:** 3

If you look at your video 'iPi Desktop Motion Capture - Technology Preview #4' you can see foot slide starting at the 12 second mark. Mind you it's not too bad, but it is evident. It looks like you're only using 3 cameras so that might be it.

Thanks,

Dave

Greenlaw · **Posted:** Tue Jul 05, 2011 10:40 am

Ursine wrote:

If you look at your video 'iPi Desktop Motion Capture - Technology Preview #4' you can see foot slide starting at the 12 second mark.

The video you're referring to is 'ancient history' and was created using a early beta version of the software about three years ago. The software has significantly improved since then, especially in this past year.

G.

Edit: Sorry, I thought you were referring to another video, but the one you did refer to was also done using a pre-release beta version about two years ago.

Ursine · **Joined:** Thu Jun 30, 2011 5:45 am **Posts:** 3

Can you point me in the direction of some recent raw captures that might show more stable feet?

Thanks,
Dave

Greenlaw · **Posted:** Wed Jul 06, 2011 11:32 am

Jean Dellac has very interesting examples on his YouTube channel:

MoCap - 6 cameras rig - first results

I'm tempted to show some of mine but it will have to wait until we're done with the short film. We really only have one walking shot in the film but FWIW it is pretty solid. The main issues we're dealing with have more to do with the fact that my characters have really HUGE heads. Tip: if your characters have BIG heads, make sure you perform as if you have a BIG head. :)

Anyway, the best way to find out if iPi DMC is stable enough for your standards is to just try it yourself. You can try iPi DMC for free for 30 days.

G.

Edit: If you're curious, here's a recent screen cap video I posted. No walking though, just big head: Motion Capture for Sergeant Marshmallow.

I should mention that the mocap data shown here is from last fall (2010) when we were still using four cameras. Recently we've been using six cameras for mocap and have done a few simpler shots using the Kinect, and the results have been pretty stable.

Greenlaw · **Posted:** Wed Jul 06, 2011 11:47 am

Hmm. Sorry to get off-topic but in re-watching Jean's footage, I'm feeling tempted to recapture s01-s07 mocap for Sergeant using the six camera setup. I was never happy that in tracking the four camera shots, DMC seemed to have trouble picking up on the hand 'fanning' motion at the end of this data. (This motion might have been too small or too fast for four camera tracking.)

Or, maybe not. At this stage, it's probably easier to just keyframe the arm motion. :p

G.

Foot Slide

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