Motive Direct to Unity Skeleton Re-Targeting is inaccurate

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bteitler
Posts: 18
Joined: Thu Jun 12, 2014 12:57 am

Motive Direct to Unity Skeleton Re-Targeting is inaccurate

Post by bteitler » Fri Sep 09, 2016 6:40 pm

The re-targeting provided by the direct Unity plugin seems to not provide a one to one correspondence between the source (i.e. Motive) bone angles and root (hip) position. It is pretty close, but is off enough that it is problematic for my use case. Here is an example video that focuses on the foot plants in a walking animation in slow motion which makes the problem quite visible:

https://www.youtube.com/watch?v=GmYyIHa ... e=youtu.be

Note that I understand completely that motion on a re-targeted Unity Mecanim skeleton will not look exactly the same as the skeleton rig in Motive due to different bone lengths on the target model and bone weights for the target model skin. However, it appears that the joint angles for the bone correspondence and root transform don't even match up, which I would expect to be the same. There is a lot of lateral sliding on the feet which doesn't seem to be explainable by different skeleton dimensions.

It is unclear to me if this is a problem with the plugin or a bug in Unity's muscle space re-targeting. I tried to do my own implementation of re-targeting on top of simple BVH files and ran into similar issues. My thread on this issue on the Unity forums is here:
http://forum.unity3d.com/threads/mecani ... on.430381/

bteitler
Posts: 18
Joined: Thu Jun 12, 2014 12:57 am

Re: Motive Direct to Unity Skeleton Re-Targeting is inaccura

Post by bteitler » Sat Sep 10, 2016 3:00 pm

Looks like this is indeed caused by the muscle space transform, which seems to assign the hip bone translation as some sort of center of mass calculation in some normalize fashion with respect to the floor plane. I think the motivation Unity has for this is to help re-align the motion with respect to the floor plane automatically for different skeleton dimensions. However, this is probably not what is wanted in all cases. You might want to add an option to override the hip bone to the true offset after the muscle space transform.

Shagan.Overman
NaturalPoint Employee
NaturalPoint Employee
Posts: 19
Joined: Mon Mar 21, 2016 2:02 pm

Re: Motive Direct to Unity Skeleton Re-Targeting is inaccura

Post by Shagan.Overman » Mon Sep 12, 2016 2:33 pm

Our developers are actually on the phone with them right now. Issues like the Inverse kinematics in mecanim are something their team is fully aware of and working on now. Unfortunately there's not much we can do from our end to improve the situation while we wait.

I'll forward your comments to the dev team.

If you need something thats works today you might look at our Unreal plugin in combination with Ikinema Live Action. https://www.youtube.com/watch?v=a32sHf7HxUM
-------
James Shagan Overman
Customer Experience Manager
shagan.overman@optitrack.com

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