It appears that splats’ orientation components do not agree with rotation of the scene’s meshes. In the example below, I create a disk and Gaussian splatting with a single splat. I use the same quaternion (x=0,y=0,z=1, w=1) for the disk’s rotation and for orientation of the splat. As you can see, their orientations do not match
Splats are rendered as 2D planes facing the camera but there are not.
They are oriented 3D ellipsoids that are projected and appear as 2D planes.
Imagine them as some kind of Zeppelin.
Math is a bit complex but at their heartm they are volumetrics.
With an identity quaternion and uniform scale, a splat appears as a spherical object.