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jdexforwords
09-04-2006, 09:05 AM
This topic might be a bit tricky to get the whole idea at the first sight, but I appreciate it if you could spend time on understanding what I meant to say.

When I setup the arm, I want to have them an ability to switch between IK and FK back and forth. I use classic 3 arm blending way. Then I write a script in order to snap IK and FK. From IK to FK is easy one, but FK to IK is tough.

I can do something like this. PointConstraint the IK control into FK wrist. delete the constraint. PointConstraint PoleVector control into FK elbow. then delete it. It actually snaps from FK to IK pretty nicely, except for one case, and this is my point.

The way I mentioned works only when FK_forearm joint was rotated in hinge axes. But most of the case Animator want to have a ball joint in FK elbow area, rather than hinge joint.

I have been thinking alternative way, but it seems logically impossible. As long as Maya uses RPsolver, which stands for Rotate Plane, IK chain can't snap into FK rotation accurately. Did you get my point?

So my question is what's the solution for that? I know one solution would be to limit the rotation axes of FK elbow so that it would act like hinge joint. But that's not what I want. I don't think all of big production limits their FK elbow. There must be some ways.

Any thought would be appreciated.
isoparmB
09-04-2006, 11:36 AM
The method of point constraining the pole vector to the elbow and the ik to the wrist temporarily should work, what was the issue you encountered with it? Was it that the joint rotation values on the elbows didn't match because the ik elbow rotated in one axis while the fk one had all three axis moving, which in turn gave a different skin deformation result?
jdexforwords
09-04-2006, 12:47 PM
Was it that the joint rotation values on the elbows didn't match because the ik elbow rotated in one axis while the fk one had all three axis moving

Precisely.

I wonder if there's any way to avoid that other than limitting elbow as hinge joint.

Well, as I type this, I feel stupid because I'm saying answer by myself. As long as maya calculates IK joint orientation by evaluating Rotate Plane, there's no way to match FK to IK in accurate way. My original question meant to be like this, How do the big production handle this issues? Animator wants to have ball joint in FK elbow, but they wants to switch.
isoparmB
09-05-2006, 02:04 AM
I'm thinking unless it's a cartoon setup, you should just lock the other two axis in the elbow joint for the fk setup. The very nature of an elbow, at least from a biped's perspective, is that it only bends in one axis: the flexibility comes from the ball joint of the shoulder. I don't think it should be any different in cg. It's just a matter of your animators getting used to that workflow where they pose the general direction from the shoulder and get the extension from the elbow joint.
animationrigs
09-06-2006, 06:19 PM
I've worked with both.
FK elbow locked ie (limited to hinge) so snapping works fine
FK elbow is completely free to move in all axis (pain for snapping).

It's great to have the freedom as an animator to "break the arm" so in that case (we didn't have proper snapping) we just didn't snap or we got the snap as close as possible and then animated through it if need be.

not necessarily a solution, but you had asked what a production does.
jdexforwords
09-07-2006, 07:00 PM
Thank you both.

It seems like having "close enough" snapping is way to go now.
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