Joint Orientation Question

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  03 March 2013
Joint Orientation Question

Well my questions about joint orientation are the following:

How does the orientation affects the rig?
How does the orientation of the joints affects the animators job?

Does it matter which axes are use to aim and to be the up axis? For example i have seen that the default arrangement is to use the Y axis to Aim and the Z axis to be the Up axis. Does it change something if i use X as the aim and Y as the Up(or any other different arrangement possible)?

Thank you for your time.
  04 April 2013

Well, I believe which axis points to where depends on what the rotation order is. You usually want the twist rotation axis to be the aim axis of the joint.

Cactus Dan
It doesn't matter what people say about you, just as long as they're talking about you., cactus3d-Plugins, CD Character Plugins forum
  04 April 2013
there are many ways both joint orientation and rotation orders can affect an animator.

First, Joint orientation is important, it really doesn't make much difference which axis you put where, but it's more important to be consistent. so that arms rotate with the same axis's on both sides, or to spread the feet is +X on both feet, not -X on one side and +X on the other, or twisting is always on the X. you have to give the animators consistent controls (rotations) throughout the rig.

Rotation orders are important because they dictate how a particular object solves it's rotations. Gimbal lock is the result of poorly set rotations order (sometimes it's unavoidable depending on the animation) but a general rule, is that the Middle axis in a rotation order is where gimbal lock lives. You want your least used rotation in the middle, if this middle axis rotates 90 degress - you've got gimbal lock. So I assess how an animator will move/use a particular control and set my rotation order to fit. You basically want your dominant rotation last in the order. the last rotation axis in the rotation order will cause all the other rotation bands to follow, view this is gimbal mode, the entire manipulator rotates with the last axis. the least used axis goes in the middle, this again is the axis that will cause gimbal lock, so plan this accordingly. and the second most used axis should go first, the first axis in a rotation order will not rotate any of the other axis's.

Always use the rotation manip in gimbal mode to see the effect of switching around rotations orders. I almost never use the default of XYZ.

rotation orders, and joint orientations are things that need to be consciously thought out before things get too complex, as often times changing these after expressions, constraints, and connections can cause problems.

an entire book could be written about the subject and Euler angles, but this should get you started and your brain thinking.

  04 April 2013

Thanks for both of your answers now i have a better understanding of joint orientation and orientation order, i certainly have lots to think about and experiment with.

Once again thank you very much
have a good day
  04 April 2013
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