[Robotics] IK Chain Joints ? pt1

[Florian Lier]

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
>
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