during a production last year we encountered an issue with Mayas Skin Cluster. As we worked on real world scale, where 1 unit is 1 centimeter, our characters moved across a environment approx. 1 kilometer length. This means our characters moved 500 meters to each side of the worlds origin. So far there was nothing obvious going on the scene. But at one point we had to troubleshoot some jittering with simulated nHair curves.
And we found out: The farer we move away from the world origin, the more inaccurat the evaluation of the meshes vertices gets.
I know that you have to be careful, when it comes to scene scale and decimal places. But I always thought, that this is a general issue with the evaluation in 3D space.
But when created a testscene, I found out, that direct transformation value change with constains are not a problem at all. No matter how far an object is placed or moved from the world center, there are always enough decimal places for a correct evaluation. However, if there is either a lattice, cluster, skin cluster or wrap moving a meshes shape components away from world center, decimal places are cut off relatively to the unit by 10. So, I assume that the effect will be always occur, becoming more and more visilble, with increasing distance to world center.
In our case an object moved by a skin cluster 400 meters away from the world center caused an inacuracy by a few milimeters, which results in vertices jittering. When I did an extreme displacement of 1000000 meters (which is a lot, I know), there are no more decimal places left and the vertices will always be moved by 1 unit, which results in extreme vertex jitterung. The effect not only shows up be moving the object, it also happened, when navigating the camera. A third Display evaluation inaccuray then was added by Viewport 2.0. (Which is less a problem, while not rendered, a least with renderers, thar are not the Hardware Renderer)
Getting back to our hair problem: I think the inaccuracy in deformer evaluation could cause the hair curves to jitter. This also could be an issue when rendering a velocity pass. Because often, when a non moving object (no camera movement either) still had velocity changes, which resulted in a slightly blurred image.
Long Story short:
If anyone has similar stuff happen, or some workaround or knows something about this issue, i appreciate the help. This happen more or less with cluster, skin cluster, lattice and wrap deformers but not with translation values. I did not tested the wire, shrinkwrap, wrinkle or jiggle deformer.
Test Scene Results:
Georg & Peter