[Robotics] IK Chain Joints ? pt1

[Benoit Bolsee]

Tail = pose.tail

Indeed, the bone matrix/head/tail are fixed, they correspond to the rest
pose.

Benoit

> -----Original Message-----
> From: robotics-bounces at blender.org 
> [mailto:robotics-bounces at blender.org] On Behalf Of Florian Lier
> Sent: mardi 14 juillet 2009 18:07
> To: Blender and Robotics
> Subject: Re: [Robotics] IK Chain Joints ? pt1
> 
> 
> Hey,
> 
> sorry - but it just came into my mind:
> 
> "poseMatrixTail is simply poseMatrix where the 4th column is 
> replaced by tail."
> 
> What's tail? The bone.tail vector?
> 
> Cheers, Florian
> 
> 
> 
> Benoit Bolsee wrote:
> > The joint information is lost after the IK constraint 
> resolution, you 
> > must recomputed from the pose channel matrix. The 
> localMatrix will not 
> > be useful in this case, it containts the transformation matrix from 
> > the rest position to the current pose position for the 
> bone, this is 
> > not directly related to joint value except for the root bone.
> >
> > One thing you can do it get the poseMatrix for each bone down the 
> > chain, starting from the root and compute the relative 
> tranform from 
> > one bone to the next by this formula: relativePose[n] = 
> > inverse(poseMatrixTail[n-1])*poseMatrix[n]
> > where n is the bone for which you compute the joint values and 
> > poseMatrixTail is simply poseMatrix where the 4th column is 
> replaced 
> > by tail. For the root bone, poseMatrixTail is the identity matrix.
> > >From relativePose you can retrieve the joint value using euler 
> > >formula.
> > Note that this will give you joint value that are 0 when 
> the bones are 
> > aligned. This does not take the rest pose into account and will not 
> > necessirily give you the correct join value (in Blender 
> joint=0 when 
> > the armature is in the rest pose by definition).
> >
> > To get the real joint value, you will need to work the bone 
> matrix. I 
> > would have to think a bit more to find the correct formula.
> >
> > Hope this helps,
> > Benoit
> >
> > -----Original Message-----
> > From: robotics-bounces at blender.org 
> > [mailto:robotics-bounces at blender.org]
> > On Behalf Of Florian Lier
> > Sent: lundi 13 juillet 2009 22:03
> > To: Blender and Robotics
> > Subject: [Robotics] IK Chain Joints ?
> >
> >
> > Hello everybody,
> >
> > I need some help concerning an IK Chain and "hinge" Joints. I've 
> > moddeled a robot arm which has an ik solver at its ik-chain 
> top. The 
> > bones are limited (XYZ) to the appropriate DoF of the joints. I can 
> > get the poseMatrix of each bone, no problem so far...BUT the 
> > poseMatrix of each bone is a summation of its parents and the bone 
> > LOC/ROT/SIZE of itself. What I need is the angle (Quat/Matrix .. 
> > whatever) between one bone of the chain
> > and its direct parent (like "real" joints which have one DoF). I
> > couldn't figure out how to compute
> > this correlation. Is there any approach?
> >
> > If you need an impresion of the arm have a look at this: 
> > http://vimeo.com/5503690
> >
> > I've also tried the localMatrix...
> >
> > THANK YOU...
> >
> > Florian
> >
> > _______________________________________________
> > Robotics mailing list
> > Robotics at blender.org 
> > http://lists.blender.org/mailman/listinfo/robotics
> >
> >   
> 
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