What are your motion blur settings when rendering this? Can you be more clear as to what the artifact is exactly? I’m not sure what is wrong from looking at this image. Perhaps it would be useful to post a render of the same frame without motion blur.
What are your voxel size settings? You should compare the results of halving (or quartering) the voxel size and doubling the voxel filter radius. You might see this sort of behavior if your voxels are really big on-screen, and your filter radius is 1.
Here’s the frame work for understanding the problem:
- There is a 3D lattice of sample points (ie. voxels) in space separated by “Voxel Size” units in each dimension.
- A particle’s values are filtered onto these voxels using its “Position” channel, and a filter with radius “Voxel Filter Radius”.
- As a caveat to number 2, the weights from the filter are normalized so that the entire energy of the particle is present in the voxel field.
If you have a single particle with “Voxel Filter Radius” of 1, this essentially means that the particle contributes to exactly the 8 nearest lattice points. This is essentially a trilinear interpolation. If this particle is assigned a high density (which most people seem to do when testing this), all 8 lattice points will get a density that is fairly high, no matter where the particle lies in between.Now, as we move this particle across the boundary of where it contributes to a different 8 set of lattice points, you will see an apparent jump of the cube (ie. aliasing).
This is negated by picking a higher filter radius, so the relative size of a voxel versus the size of the particle allows for a better reconstruction of the density function.
Is this relatively clear, or should I try to make some illustrations?