Dan Wood

Heh, it's fairly rare to get properly-technical (how does this node work) questions answered on here I find :-)

As I understand it Gas Particle to Field does at least that - I assume it sums a linear interpolation of the velocity and weights between the 8 cells each particle is closest to, then divides one by the other. Not sure if it can do/does more elaborate kernels, or keeps it simple for speed.

(Ah, although I just remembered it extrapolates velocities into unoccupied cells too, so I guess it's a bit more complex than that)

I'm not sure anyone besides SideFX themselves could say what the maths behind microsolvers is. Might be worth reaching out to them directly...

I think the changing point count might be throwing off the deforming-geometry sourcing for the collider... it's more for actual deformation, not partial-deletion.

Try having each half be a separate, non-deforming static object, then just "switch off" the top one... not sure if there's a more elegant way, I've used a Switch DOP.

Mantra/Karma both unhide the vm_image_exr_dwa_level (DWA Compression Level) parameter if DWAA or DWAB exr compression is selected, and lets you change the compression level from the default of 85 - but in COPs (both latest Copernicus 20.5.550, and old COPs, at least since 19.5 it would seem), that option never appears, and if I add it manually from the Render Properties tab, it gets ignored - COPs seems to always output at 85.

Is there a way to set the compression level in COPs correctly, or does this seem like a bug?