When blending rotations, the time editor seems to do some strange things. The problem showed up in the middle of a blend between two motion capture clips. The elbows would flicker from around a regular 90 degree bend to a 90 degree bend the wrong way, a 180 degree flip.
The rig is pretty complicated with a source mocap data hierarchy (where the issue is coming from), an offsets hierarchy and our regular animation rig. I wanted to eliminate as much complexity as I could so I have replicated the problem with only the source hierarchy (probably could do it with two cubes though to simplify further) using two very simple single pose clips. I have one clip with a static pose with an elbow bend of -80 in the channel box, and another with the exact same static pose but with a -100 degree rotation. Visually this blend looks ok but…
Here is how the blend goes in the channel box:
0% -80
50% -90
51% 269
99% 260
100% -100
Why!??! I get that rotations sometimes do weird things trying to find the shortest route from a to b but the shortest and simplest way to do that in this case seems to be to go from -80 to -100 through -90. It starts out well enough but why would it flip 360 at 50% to then count backwards to the target rotation to then snap 360 back again?? Once rotation is added from any other axis in either clip you start to see a rotation round the back rather than a snap but the core problem i guess is the way this initial rotation is calculated.
Can anyone offer any help? Are there any rotation interpolation options I need to look at?
Thanks
Adam