Deborah R. Fowler
Fluids - Pyro
Posted: May 2 2020
Updated Feb 14 2021
See Introduction to Pyro
SPARSE PYRO
How does a sparse pyro differ? One of the problems with classic pyro was keeping up with fast moving sources in terms of the resize container. Many solutions were used, however sparse pyro eliminates the need for things like clustering
This has substantially changed from the
non-sparse solver.
- pyro (SmokeObject
Sparse) - controls the resolution of your simulation
but now labeled Voxel Size
- source_density (or fuel) - Volume Source - similar to the non-sparse, bringing in the density and temperature fields
- pyro solver (sparse)
https://www.sidefx.com/docs/houdini/nodes/dop/pyrosolver_sparse.html
Calculations are done in the areas of interest
only. These are determined by the reference fields in the
resizing subtab in the advanced tab. Positive areas are flagged
as active, this region is dilated.
This can be visualized if you enable Active Region under the
guides of the smoke object (sparse), below for sparse fireball.
PYROSOLVER (sparse) tabs
The look has substantially changed from the non-sparse solver. However we are still looking at similar controls. Below are the Simulation and Shape tabs for sparse.
For comparison these are the non-sparse
The controls are similar in some cases. In particular, dissipation is familiar, as well as many of the shape controls. In addition there is a pyro SOP node which integrates the controls and adds a Look tab.
In the SideFX documentation section on differences between legacy and sparse pyro, fuel was used and would ignite and then the burn field was linked to heat so that heat and burn accumulated to generate outputs.
The new workflow for H18 requires the burn to be generated in SOPs and brought in as part of sourcing to give more control. In 17.5 the workflow was shifted to point source so this gives an excellent way to shape your pyro.
In the legacy solver voxels were created for the simulation using bounding boxes. Even when adaptive, this causes issues, particularly with fast moving pyro. Sparse volumes create information where the volumes are, but these areas communicate. (An analogy is VDB versus standard volume). There is still a padding parameter that can be adjusted should your pyro get clipped. Entagma has an excellent benchmark comparison for speed on vimeo.
Excellent short videos from Entagma (in H18, not 18.5) on sop level:
- sparse Billowy Smoke with pyro sop solver by Entagma.
- I highly recommend walking thru this tutorial even though you can get the same results from the shelf tool it will help understanding
- I have created a sticky noted hipnc file created now in Houdini 18.5 if you get stuck
- spreading fire Pyro Fx | Spreading Fire by Entagma
- I have created a sample file now in Houdini 18.5 if you get stuck