This parameter must be enabled if you intend to perform a sparse smoke simulation; see the sparsity section of the solver’s help card for more information.

Enable this option if you want to perform a two-dimensional simulation.

The size of each simulation voxel. Smaller voxel size corresponds to a higher resolution simulation (more detail, but slower).

This multiplier is applied on top of Voxel Size to determine size of velocity voxels. Larger values of this parameter thus correspond to lower- resolution velocity fields, which will simulate faster but produce less detail from the motion.

The starting location of the simulation container. If Max Size is turned on, this parameter also specifies where the bounding box is centered.

By default, the container will grow as the simulated smoke and fire inside it evolve. Enabling this option allows you to set a maximum size the container may grow to.

Determines if the creation frame refers to global Houdini frames ($F) or to simulation specific frames ($SF). The latter is affected by the offset time and scale time at the DOP network level.

The frame number on which the object will be created. The object is created only when the current frame number is equal to this parameter value. This means the DOP Network must evaluate a timestep at the specified frame, or the object will not be created.

For example, if this value is set to 3.5, the Timestep parameter of the DOP Network must be changed to 1/(2*$FPS) to ensure the DOP Network has a timestep at frame 3.5.

Instead of making a single object, you can create a number of identical objects. You can set each object’s parameters individually by using the $OBJID expression.

The name for the created object. This is the name that shows up in the details view, and is used to reference this object externally.

When turned on, newly created objects are solved by the solver on the timestep in which it was created.

This parameter is usually turned on if this node is creating objects in the middle of a simulation rather than creating objects for the initial state of the simulation.

By preventing a large object from being cached, you can ensure there is enough room in the cache for the previous frames of its collision geometry.

This option should only be set when you are working with a very large sim. It is much better just to use a larger memory cache if possible.

The created object will contain a flame field when this parameter is enabled. This field is used by pyro simulations that involve combustion or light emission. You can turn off this toggle as a very minor optimization if the simulation will not make use of the flame field.

Controls the sampling pattern of the velocity field. Center sampling yields faster simulations, but may give rise to some artifacts (which may be fixed with the help of Hourglass Filtering controls on the solver). Face sampling is slower, but does not suffer from any artifacts.

This parameter specifies the initial state of the velocity field, as well as its default external value. This parameter can be set to endow the smoke with a natural travel direction, as if it were influenced by a strong uniform wind force.

Controls the sampling pattern of the divergence field, which can be used to add expansion/contraction to the velocity field. Center sampling should generally be faster if you are adding expansion from one of the fluid’s fields at simulation time.

When Velocity Sampling is set to Center and all modifications to the divergence field will go through a Volume Source (this includes having Add Expansion disabled on the Pyro Solver), then setting Divergence Sampling to Corner will be faster.

When this option is enabled, Cd and Alpha fields will be added to the smoke object, containing the smoke color and color amount, respectively. If the Pyro Solver detects the presence of these fields, it will ensure to evolve them as the simulation advances.

This parameter specifies the default color of smoke and the initial state of the Cd field.

Controls the initial (and minimum) value of the Alpha field. Intuitively, the fluid will contain Default Alpha amount of dye of Default Color at the beginning of the simulation.

Relative path for Position data. This will be used to transform the fluid box, allowing for non-axis aligned fluid simulations. As the sparse solver is efficient in its use of memory, you don’t need to use this most of the time, even in situations where smoke is blowing diagonally.