I'm a newish user to Houdini. I've been following along with a few of John Kunz's streams, and he has a really interesting set up for pyro/smoke where he rasterises attributes inside the solver instead of outside using a gas particle to field DOP.
I am currently trying to source Cd as a volume using this set up, and I can't work out why I can't visualise it when using a volume visualise node post sim. It appears on frame one, and then disappears. When I only visualise density I can see the smoke in full, but when the Cd volume is added to the diffuse section it just disappears.
Try adding an Alpha of 1 to your points and sourcing it the same way you do Cd. Alpha is the mask with which the Cd field is composited on your default smoke color.
That definitely helps make colour visible with the volume visualise, however, the colour is still staying only within/close to the source object. I've added a Gas Advect Field into the advection input of the smoke solver (with Alpha and Cd in the field section) but they are not visibly advecting like density is.
The smoke solver will advect Cd and Alpha by default, no need to add the Gas Advect Fields. The problem is that your Cd sourcing is set to copy, so it's basically replacing the entire field with your source at each frame. The correct way should be to blend it on top of your existing field using the Alpha, but I'm not sure how to do it with your setup, maybe somebody else can chime in.
