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

Ben Sunshine-Hill <[email protected]> Fri, 14 Dec 2012 10:35:20 +0000
Newsgroups gmane.games.devel.algorithms
Message-ID <CAGZipVGb5fqK1LRHaJdETfTeYu+dsES+V+FdAOc229DZEYYBRQ@mail.gmail.com>
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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 <
[email protected]> 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 <[email protected]> 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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Ironically, that paper actually compares joint orientations instead of poin=
t clouds. For point cloud-based pose similarity estimation, Kovar&#39;s ori=
ginal motion graph paper is probably a good reference.<div><br></div><div>

<a href=3D"http://pages.cs.wisc.edu/~kovar/mographs.pdf">http://pages.cs.wi=
sc.edu/~kovar/mographs.pdf</a><br><br>Ben</div><div><br></div><div><div cla=
ss=3D"gmail_quote">On Thu, Dec 13, 2012 at 9:12 PM, Michael De Ruyter <span=
 dir=3D"ltr">&lt;<a href=3D"mailto:[email protected]" target=3D"_b=
lank">[email protected]</a>&gt;</span> wrote:<br>

<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">Also with the triangle normal idea, a notion=
 of distance is missing,<br>
so you should add something like distance hips - hand, hips - foot,<br>
foot - foot, etc to your comparison algorithm if u were to try this<br>
method.<br>
<br>
Though since there is already a paper on the point cloud approach,<br>
it&#39;s probably safer to start with it.<br>
<br>
Sent from my iPhone<br>
<div class=3D"HOEnZb"><div class=3D"h5"><br>
On 2012-12-13, at 12:47 PM, Richard Fine &lt;<a href=3D"mailto:[email protected]=
et">[email protected]</a>&gt; wrote:<br>
<br>
&gt; On 12/13/2012 8:09 PM, Michael De Ruyter wrote:<br>
&gt;<br>
&gt;&gt; - when comparing local quaternions for the joints, the comparison =
will take into<br>
&gt;&gt; account the twist around the limbs even though any amount of twist=
 doesn&#39;t<br>
&gt;&gt; change the position of the limb. Therefore you could get drastic d=
ifferences<br>
&gt;&gt; when visually there are barely any.<br>
&gt;<br>
&gt; True in the general case, but I&#39;m using a hierarchical setup, so a=
 twist<br>
&gt; in an upper arm can drastically change the position/orientation of a<b=
r>
&gt; forearm and so on. It matters less and less as you approach the leaf<b=
r>
&gt; nodes, but this is something I intended to eliminate with weighting.<b=
r>
&gt;<br>
&gt;&gt; - even if the joint orientation are different the position of the =
limbs,<br>
&gt;&gt; especially their endings like hands of feet, could still be in ver=
y close<br>
&gt;&gt; positions, i.e. potentially closer than limbs with similar rotatio=
ns but with<br>
&gt;&gt; their root joint (shoulder for instance) off by a bit. =A0You ment=
ion weighting<br>
&gt;&gt; system, but that is going to be a pain to tune.<br>
&gt;<br>
&gt; Ah, yes, OK. I&#39;d assumed that a pose with leaf-node discrepancies =
would<br>
&gt; be less visually different than one with trunk-node discrepancies, but=
<br>
&gt; that&#39;s not a sound assumption.<br>
&gt;<br>
&gt; This sounds like it would be a problem for *any* hierarchy-based<br>
&gt; approach, so anything based on comparing local-space positions is<br>
&gt; probably a non-starter.<br>
&gt;<br>
&gt;&gt; An other approach would be to find a comparison algorithm that com=
pares the<br>
&gt;&gt; overall position of the limbs.<br>
&gt;&gt;<br>
&gt;&gt; For instance you could consider;<br>
&gt;&gt; - modeling triangles based of significant body joints, for instanc=
e<br>
&gt;&gt; =A0 =A0 =A0+ hips, shoulder, hand<br>
&gt;&gt; =A0 =A0 =A0+ hips, hand, foot<br>
&gt;&gt; =A0 =A0 =A0+ hips, shoulder, shoulder<br>
&gt;&gt;<br>
&gt;&gt; Then use the normal of those triangles for your pose comparison.<b=
r>
&gt;&gt;<br>
&gt;&gt; You would still need to make the normals relative to the hips and =
then use a<br>
&gt;&gt; hips orientation comparison process.<br>
&gt;<br>
&gt; Right OK. Sounds similar to the point cloud approach, maybe a little<b=
r>
&gt; less prone to small discrepancies, as using the normal instead of the<=
br>
&gt; joint positions would equate similar triangles.<br>
&gt;<br>
&gt; Cheers!<br>
&gt;<br>
&gt; - Richard<br>
&gt;<br>
&gt; ----------------------------------------------------------------------=
--------<br>
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