xyz quaternion covert to quaternion in splishsplash

[BinglunWang]

Hi,

I'm trying to set rigid bodys quaternion q=(w, x, y, z) form pybullet which is a xyz coordinate to splishsplash xzy coordinate q'.

Do you know how to convert the q to q' in splishsplash? It seems depend on the implementation of splishsplash rigid body system?

Sorry about the different camera position.

Ground truth:
Figure 1,

I tried:
Figure 2, directly swap y and z to make q' = (w, x, z, y) in splishsplash.

Figure 3, as it might flip the chirality, so I make q' = (-w, x, z, y) or q'= (w, -x, -z, -y)

[janbender]

How do you set the quaternion in SPlisHSPlasH? Do you use the constructor: Quaternionr(w,x,y,z)?

[BinglunWang]

Yes. Thank you for your answer. It indeed the bug from quaternion order.

And it works now!!

[janbender]

If you use the .coeffs() function, the order is (x,y,z,w).

[BinglunWang]

I also made a 5 mins explanation to explain why we need to convert quaternion to q = (-w, x, z, y).

https://www.youtube.com/watch?v=VO0ol6qCOOc&t=2s
Hope the video can help other people have the same issue.