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

[Michael De R. <mic...@gm...>]

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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