QuaterNet: A Quaternion-Based Recurrent Model for Human Motion(github.com)
github.com
QuaterNet: A Quaternion-Based Recurrent Model for Human Motion
https://github.com/facebookresearch/QuaterNet
8 comments
Wait, so previous ones didn't consult the literature for animation systems and how (at least the ones I know) most of them nowadays use quaternions because of discontinuities and gotchas? That seems weird, even if you don't care about ik, quaternions have very nice properties for animation systems, and only add an extra variable (4 vs 3) so aren't too much of an overhead compared to reduced error handling or going all the way to 3x3 matrices.
I assumed that too until I read this slightly grouchy but very interesting thread: https://github.com/KhronosGroup/glTF/issues/1515
Did they in the end settle with quarternions as glTF is an export format (same playback on different apps) and not an authoring format?
Rotations in GLTF are specified with quaternions.
Ha, sadly no! Whereas it's unacceptable for let's say an airplane to use euler, or a modern video game camera engine...
Most animation software used by artists/animators uses euler angles, and in order to deal with gimbal lock they just... Use a 2 or even 3-child hierarchy (they call it "controllers") where each controller animates one axis (or two). That's a huge overhead compared to just using quaternions, but if it makes animators more productive it's probably worth it. Computer vs Human time. Especially in situations where render farms are used and a frame takes an hour to be rendered, does it really matter?
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So, it's not the animation applications fault. it's the animators who always prefer euler + messy scene hierarchy :) I 've even see robotic arms be animated like that... robotic arms!
Most animation software used by artists/animators uses euler angles, and in order to deal with gimbal lock they just... Use a 2 or even 3-child hierarchy (they call it "controllers") where each controller animates one axis (or two). That's a huge overhead compared to just using quaternions, but if it makes animators more productive it's probably worth it. Computer vs Human time. Especially in situations where render farms are used and a frame takes an hour to be rendered, does it really matter?
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So, it's not the animation applications fault. it's the animators who always prefer euler + messy scene hierarchy :) I 've even see robotic arms be animated like that... robotic arms!
I was wondering about the advantage of quaternions over matrix/vector algebra, and found this quite interesting post:
https://stackoverflow.com/questions/8919086/why-are-quaterni...
https://stackoverflow.com/questions/8919086/why-are-quaterni...
Recurrent neural networks for modeling physical systems are starting to really come into their own. We have a few exciting years ahead of us.
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