removing RBD from a sim

Sometimes you need to remove an RBD from a sim completely. Eg, you're using a block to push something and then need it to get out of the way...

Make sure you have a group for it on SOP level. It will probably be a point group, as you're most likely using packed geo.

Now use a SOP solver in your DOP network. Attach it to a multisolver, alongside your Bullet/RBD solver..
Inside the SOP solver, blast the group that you created earlier. Use a switch node or some other timing device (you could use a point wrangle with removepoint I think)  to trigger the group's deletion.
Eg. Switch node  could use $F>1000. Here it will switch from "all the geo" to "all the geo minus the group" input.

latticing VDBs/volumes

Bring in your VDB however you need to.
Plug it into a VolumeVOP and create an addpoint node. Plug P into the ptvalue input.
Next create a setattrib node and plug your addpoint's ptnum output into the setattrib's i1. Plug your density into the value node and name the parameter "density". Jump back out of the VOP.

This will have made a volume grid of points that represent your VDB, each containing the corresponding density value. The number of points created is dependent on the resolution of your VDB, although I guess you could duplicate points and hope that they interpolate nicely?

Next, add a Timeshift node after the VOP and freeze your volume at the point you think it occupies the most space. Eg. if it's a trail of cigarette smoke, it's last frame. Create a Bound node for this.
This is now the lattice you can transform and deform.
Then make a Lattice node and plug your Volume VOP into the first input, the output of the Bound into the 2nd and then finally whatever your transform/deforms are into the 3rd.

So far, we've transformed a bunch of points, that hold our density values.. Now we have to recreate our volume..


Connect a Bound node to your deformed points. We're making an empty volume that encompasses the limits of your deformed sequence. Add an Iso Offset to this, set the Output Type to Fog Volume, Mode to Ray Intersect and name it Density. You control the effective resolution with the sampling. Next let's copy the density back into your empty volume.

Make a volume VOP, plug the Iso Offset into the first input & the lattice into the second. Jump in and make a Point Cloud Open node. Connect the P to the P and the OpInput2 into the File input.
Create a Point Cloud Filter and set it's signature to Float Channel and label the Channel "density". Plug the Point Cloud Open's handle into the Point Cloud Filter's handle input. Finally plug the value into the volumevopoutput's Density..

Your blank volume now has a deformed version of the original's density!
Sit back, relax and pretend you're resimming now.

Pyro UPRES

Setup a Pyro as you would normally..This will be your low res sim. In a Geo sop somewhere, make a DopIO node and choose the pyro preset to make sure you're importing all the required fields from the low res sim. You could file cache this out..

Then..make a new Dop network. Inside this, create a smoke object and plug it into a Gas Upres node.
Point the Gas Upres node's Initial Data/Low Res Sop Path to a DopIO node you made earlier. Alternatively if you've cached it out to VDBs or bgeo.sc's you can switch the source to "file" and point it to that cache.


I've found that putting a copy of your low res sim's Source Volume helps a lot. Plug that into the last input of the Gas Upres. Switch it's Velocity setting to COPY, since you'll want to copy it from the lowres sim.

You might have to play with the smoke object's initial size settings, so that it encompasses your entire sim size. Oh - and change the division size to your desire resolution..we are upres-ing after all.

Mess around with extra dissipation or turbulence in the Gas Upres node...

That should be it.