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 MrUnderhill08-18-2006, 05:49 PMA colleague and I were having a discussion about pole vectors. Some of the animators we work with hate them and don’t like them on a rig. He has taken to setting an attribute on the arm controller and using the “twist” channel from the IK instead of a pole vector. The question that I have is does the “twist” attribute represent the same functionality of the pole vector or are they different? Thanks.
PEN
08-18-2006, 09:33 PM
Depends on what the twist value is dependant on. Been a while since I looked at it closely in Maya but if you are dealing with twist values they need to have some point of reference. That can be the parent object of the chain or the goal end of the chain. Either way it can be come hard to control in extream poses. With a pole vector you know where it is and you can better visualy see where the problems will lie.

MrUnderhill
08-19-2006, 12:52 AM

From the Maya Help...

Twist Disc

The twist disc is a manipulator that you can use to twist or rotate the joint chain. The twist disc is located at the end joint of the IK chain. Translating the pole vector often leaves the IK chain pointing in the wrong direction. You can use the twist disc to re-orient the plane after you move the pole vector to prevent flipping.

Pole Vector

The pole vector is a manipulator that lets you change the orientation of the IK chain. The pole vector also lets you control flipping.

Since moving the pole vector changes the orientation of the reference plane, moving the pole vector can also change the orientation of the joint chain directly; just as manipulating the twist disc can change the orientation of the joint chain. This is because the joint chain's degree of orientation—or twist—is defined as the difference in orientation between the reference plane and the joint chain plane.

It sounds like they are designed to be used in tandem and not exclusively one or the other?

eek
08-20-2006, 04:49 PM

From the Maya Help...

Twist Disc

The twist disc is a manipulator that you can use to twist or rotate the joint chain. The twist disc is located at the end joint of the IK chain. Translating the pole vector often leaves the IK chain pointing in the wrong direction. You can use the twist disc to re-orient the plane after you move the pole vector to prevent flipping.

Pole Vector

The pole vector is a manipulator that lets you change the orientation of the IK chain. The pole vector also lets you control flipping.

Since moving the pole vector changes the orientation of the reference plane, moving the pole vector can also change the orientation of the joint chain directly; just as manipulating the twist disc can change the orientation of the joint chain. This is because the joint chain's degree of orientation—or twist—is defined as the difference in orientation between the reference plane and the joint chain plane.

It sounds like they are designed to be used in tandem and not exclusively one or the other?

Sounds like the disc is a way of reseting the orientation of the bones against the pole vector, like a look at in max with a float list controller stuck on top. The pole vector is a way of essentially letting the solver know what plane of reference its on. As with basic trigonometry you need a plane of reference to work out the angles.

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08-20-2006, 04:49 PM
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