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

[Ben Sunshine-H. <sn...@gm...>]

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 <
mic...@gm...> 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 <rf...@tb...> 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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