Shoulder Issues
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Author:  Pat [ Tue Oct 18, 2011 9:24 pm ]
Post subject:  Shoulder Issues

Hey gang, I was running a test on dynamic cloth interacting with a mocapped character. The shoulders seem to keep "popping" out of place, whether or not I have shoulder tracking clicked.
You can see it here http://www.youtube.com/watch?v=y_6HQQ6Po84
The room was light colored and I was wearing the traditional Red sleeves under black t-shirt / blue jeans, black shoes fall fashion :)

Any ideas as to what the deal is? I was using four cams this time two were high up, about 7 feet while the others were at about 3 feet and 5 feet.



Author:  Greenlaw [ Tue Oct 18, 2011 11:10 pm ]
Post subject:  Re: Shoulder Issues

That's really weird...I don't think I've seen this before. Was it popping like that before you exported the data to Poser?

Could it be that you varied Configurable Jitter Removal during the take? If so, you need to set Trajectory Filtering to 0 and then back to your desired value. This usually smooths any 'bumps' in the motion curve.

Other than that, I'm stumped.

You might be able to fix this easily in your 3D program though. Look at the motion graph for the joints that pop. The frames where it pops should be obvious and eliminating the pop might simply be a matter of deleting the offending keyframes in the motion graph. Be sure to work with a copy of your scene before doing this kind of editing.

Good luck!


Author:  Pat [ Wed Oct 19, 2011 8:30 am ]
Post subject:  Re: Shoulder Issues

Thanks G,

I completely forgot about trajectory filtering. I'll keep that in mind next time.

Thanks again :)


Author:  RebelHill [ Sat Oct 29, 2011 9:29 am ]
Post subject:  Re: Shoulder Issues

Looks to me very much like a gimbal issue related to the crappy poser rigs.

Poser rigs usually use morfs to try and shape shoulders to make up for poor bone deformation... the problem is that these shapes are tied to bone rotation, and one thing you get quite commonly (especialy with mocap) is that a bone will "flip" 180-360deg in one or more axes to solve a given rotation... This translates into different shapes/morfs getting "popped" in, as they follow the bone rotation linking explicitly.

The only fix is to take the mocap bones, and run them through a gimbal filter which'll resample the rotations to try and remove flips... and to that you're gonna have to run through some bigger 3d package, max, maya, mb, si, etc.

Author:  Pat [ Sat Oct 29, 2011 10:32 am ]
Post subject:  Re: Shoulder Issues

Really? Interesting. Thanks for the info. Do the Daz characters have the same issues? I use this program because I hate modeling, and I thought that Poser Pro would have dumped those limitations. I think that another issue that I had was that my calibration was off and I didn't realize it until I re-read the wiki. The new video I posted only has one slight shoulder pop issue as compared to this video.

Does motionbuilder have a gimbal filter? I'm going to have to get that program anyway.

Thanks for the help. I appreciate it.


Author:  RebelHill [ Sun Oct 30, 2011 7:35 am ]
Post subject:  Re: Shoulder Issues

I should imagine so, yes...

Tbh, its got nothing to do with poser or daz rigs specifically... the same problem applies to any software.

Often (in fact, always) its impossible to get smooth, or rather CORRECT deformations at the shoulder through simple weighting (unless we're talking a VERY simple cartoon type character). One common way of fixing this is to make a series of morfs/blendshapes which "model out" corrections for certain poses of the shoulder. For ease, these can be tied to the rotation values at that joint to autocorrect (morf) the shape as you animate.

This by itself is fine. However, due to the range of motion in the shoulder, and the way that rotations are commonly interpreted (euler), the only way to transition between 2 poses in a certain direction involves flipping some of the channels at a single frame in time. When viewing just the bones, you cant see it... cos as one channel flips, an alternate channel also flips, compensating the overall pose. This ofc, gives you a hard value change in these channels between one frame and the next, and so if shapes have been tied to "follow" these values, they too will "snap" at the same frame.

Ofc, in other packages, where you have more thorough manual rigging tools, there are various ways to compensate for this... You can either euler (or gimbal) filter the curves to correct the flipped channels, or, you can resample the rotations at that point using quaternions, and use the results of the quat rotation data to drive the shapes instead (more or less whats referred to as a pose space deformer).

So yes, MB, maya, etc, all have channel filters that allow you to resample the curve data to try and avoid, or cancel out these flips as much as possible (in MB there's various types, gimbal killer, unroll, etc, each of which perform different reinterpretations/resampling of the curves).

Thing is... even with these filters... it isnt always worked out for you auto-magically... You will find that you may still need to perform manual changes here n there... or use different filters to resample different parts of the curve data.

Ofc, the simple fix, in poser, or wahtever else... is jsut to dump the morfs that are linked to the bone rotations. The flip of the bone will still happen, but you wont see it... cos the effect you are "seeing" isnt the bone flip, its the morf flip. Ofc, doing this will reduce you back to basic weighted shoulders, which will often lose volume, or look, pinchy.

Point is... you still have to make your own rigging decisions, and curve management in order to get things behaving exactly the way you want or need them to. Mocap is wonderful, but its by no means a panacea that can save you having to do other stuff manually... tahts just the way it is.

And tbh... as far as iPi goes, and wonderful as it is... I would consider it pretty useless by itself... too many inacuracies, too much foot skate, etc to be of any real value use withou having another package to edit and cleanup the resulting mocap data.

Not that thats a bad thing, ofc... Im not aware of a SINGLE mocap system out there that DOESNT require any manual cleanup.

As for what package to choose... MB is by far the leader, but if all you're looking for is some basic clean and fliter stuff, then you wont be using about 80% of the features in the package.

With that in mind, you might do well to look at Maya... it has mocap retarget and cleaning tools (brought in straight from MB, effectively giving you a "motionbuilder lite" right inside of maya). Add to this the fact that Maya is actually cheaper than MB, plus has a whole cavalcade of rigging, skinning, and animation tools that MB doesnt, and you may find it more suited to your needs.

Author:  Pat [ Sun Oct 30, 2011 9:38 am ]
Post subject:  Re: Shoulder Issues

Lot's of information, thanks for that. It's funny, the only reason I never went with Maya or 3dsMax, is because I don't model. I never considered them for MoCap issues. Since Blender has been gaining popularity over the years, I wonder if it has the channel filters you are referring to.....?

Thanks again for the detailed information. This helps me understand a lot better.


Author:  Pat [ Sun Oct 30, 2011 10:35 am ]
Post subject:  Re: Shoulder Issues

Actually, I think that BVHacker can eliminate roll bone issues and fix that shoulder issue by merging it with it's parenting. You think that would work?


Author:  RebelHill [ Mon Oct 31, 2011 5:48 am ]
Post subject:  Re: Shoulder Issues

Couldnt really say much about bvhacker tbh.

Ive NEVER gotten on well with those bvh files that use multiple bones at each joint (the extra bone is supposed to be for gimbal... meaning one bone can rotate normally to prevent the other having to flip)... a fair enough way to have things, but also not without its own hassles to deal with.

In truth, Ive never used them... Ive only ever bothered with FBX format motions, mainly due to the standardisation of it compared to bvh, and the only times Ive ever had to use one, I just sent it into MB and converted it.

Author:  Pat [ Mon Oct 31, 2011 11:41 am ]
Post subject:  Re: Shoulder Issues

I downloaded BVHacker and it seems to have worked. I using it on a test piece now which I'll post when I'm done.

Thanks for all the help :)


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