Re: [Algorithms] Finding the best pose to re-enter animation graph from ragdoll

[Richard F. <rf...@tb...>]

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