IK FK Blending 2004-07-06 - By OO's mailbot
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Actually you can get the IK solver to use the preffered rotations
parameters rather than the kinematics rotation, which means that the IK
is no longer influenced by the FK animation. However, it looks like
there is a bug in the IK/FK blending code, because if you set IK/FK to
0.5, and turn IK/FK ghosting on, you will see the FK working correctly,
the IK being solved correctly, but the result jumping around...
To test, create a 2 bone IK chain, animate the second bone in Z
rotation from -90 to +90. Then constrain the effector to a null moving
around.
Set the IK/FK ghosting and blending at 50%
then change the IK solver to use preffered angles rather than joint
rotation, and look at the difference in the pure IK ghost, then the
resulting blend.
OO
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Olivier Ozoux's mailing list robot
mailbot@(protected)
On Jul 7, 2004, at 7:11 AM, Bradley Gabe wrote:
> The main problem with XSI's built in IK-FK blending is that it stores
> the FK rotations in the preferred angle parameters, which means your
> keyframed FK animation will affect which quadrant the IK calculations
> solve for. Therefore, as long as you stay within the same 90 degrees
> of your IK solve, you shouldn't get any flipping or jitter issues.
>
> If you're going to use the 3-chain technique, make sure the chain
> that is being blended between the IK and FK chains is split into
> separate, single-bone chains (I only use multi-bone chains to do IK
> solving). I tend to use a pose constraint on them (which is faster
> than an orientation constraint) and use the built in constraint
> blending to do the mixing. It works like a charm.
>
> -Brad
>
>
>
> Hi guys
> �
> I have asked this once this morning, so please excuse my repeating the
> question but I promise it has evolved from earlier...
> �
> I gather from reading xsibase posts etc that the IK / FK blending on
> standard bones is not great, but does anyone know a workaround that
> will allow me to blend between FK of an elbow joint bending back on
> itself, and an IK punching motion? All I seem to get is pops and snaps
> when trying to blend between the 2 motions. I know I could put them on
> the mixer, but I need a true IK - FK blender to animate with...
> �
> Which led me to set up the 3 chain IK - FK rig,� IK chain, Result, FK
> chain, expressions as clips on the mixer driving the rotation / roll /
> upvector angle, but the 2nd bone in the chain doesnt update until I
> change the frame...
> �
> Any thoughts sure would be appreciated...
> �
> Cheers all
> �
> Jamie
>
>
> --
> Bradley R. Gabe
> Industrial Light & Magic
>
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