I’d think you’d want to compare not just the static configuration of the pose but also the point/joint velocities. Your ideal choice will be one where not only the pose matches well, but the body parts are also moving at similar directions and speeds to the ragdoll’s current state.

 

From: Ben Sunshine-Hill [mailto:sneftel@gmail.com]
Sent: Friday, December 14, 2012 2:35 AM
To: Game Development Algorithms
Subject: Re: [Algorithms] Finding the best pose to re-enter animation graph from ragdoll

 

Ironically, that paper actually compares joint orientations instead of point clouds. For point cloud-based pose similarity estimation, Kovar's original motion graph paper is probably a good reference.

 

http://pages.cs.wisc.edu/~kovar/mographs.pdf

Ben

 

On Thu, Dec 13, 2012 at 9:12 PM, Michael De Ruyter <michael.deruyter@gmail.com> wrote:

Also with the triangle normal idea, a notion of distance is missing,
so you should add something like distance hips - hand, hips - foot,
foot - foot, etc to your comparison algorithm if u were to try this
method.

Though since there is already a paper on the point cloud approach,
it's probably safer to start with it.

Sent from my iPhone


On 2012-12-13, at 12:47 PM, Richard Fine <rfine@tbrf.net> wrote:

> On 12/13/2012 8:09 PM, Michael De Ruyter wrote:
>
>> - when comparing local quaternions for the joints, the comparison will take into
>> account the twist around the limbs even though any amount of twist doesn't
>> change the position of the limb. Therefore you could get drastic differences
>> when visually there are barely any.
>
> True in the general case, but I'm using a hierarchical setup, so a twist
> in an upper arm can drastically change the position/orientation of a
> forearm and so on. It matters less and less as you approach the leaf
> nodes, but this is something I intended to eliminate with weighting.
>
>> - even if the joint orientation are different the position of the limbs,
>> especially their endings like hands of feet, could still be in very close
>> positions, i.e. potentially closer than limbs with similar rotations but with
>> their root joint (shoulder for instance) off by a bit.  You mention weighting
>> system, but that is going to be a pain to tune.
>
> Ah, yes, OK. I'd assumed that a pose with leaf-node discrepancies would
> be less visually different than one with trunk-node discrepancies, but
> that's not a sound assumption.
>
> This sounds like it would be a problem for *any* hierarchy-based
> approach, so anything based on comparing local-space positions is
> probably a non-starter.
>
>> An other approach would be to find a comparison algorithm that compares the
>> overall position of the limbs.
>>
>> For instance you could consider;
>> - modeling triangles based of significant body joints, for instance
>>      + hips, shoulder, hand
>>      + hips, hand, foot
>>      + hips, shoulder, shoulder
>>
>> Then use the normal of those triangles for your pose comparison.
>>
>> You would still need to make the normals relative to the hips and then use a
>> hips orientation comparison process.
>
> Right OK. Sounds similar to the point cloud approach, maybe a little
> less prone to small discrepancies, as using the normal instead of the
> joint positions would equate similar triangles.
>
> Cheers!
>
> - Richard
>
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