Quaternion order?

[namheegordonkim]

brax/js/system.js

Line 317 in b3e75f9

const rot = system.rot.map(r => [r[bi][1], r[bi][2], r[bi][3], r[bi][0]]);

Mostly FYI for those implementing their own renderers.

It seems that the quaternion coordinates used by Brax is in a different order than convention. Is there a good reason behind this?

[btaba]

Hi @namheegordonkim, yes the quat order in brax is w, x, y, z, so we do a little switcharoo to plug into THREE.js

[JoeyTeng]

With the release of JAX 0.4.12, their quaternion order is in x, y, z, w (deduced from code here) is there a plan to adapt their change and make these behaviours consistent?

[btaba]

Hi @JoeyTeng , sorry for the late reply. It looks like jax.scipy is following scipy convention, but we are unlikely to switch to x,y,z,w. We are aligning brax more with MuJoCo these days