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The Source Volume DOP is a microsolver used in building larger fluid
simulations. The 
Fluid Solver and 
Smoke Solver DOPs allow
microsolvers to be added before or after the main solver step to extend
or tweak the simulation. Alternatively, advanced users may attempt to build an entire new solver out of microsolvers.
The Source Volume DOP imports volumes and binds these to the specified DOP fields.
Any combination of volumes can be loaded and mapped. A set of default combinations are presented as presets.
These work together with the 
Fluid Source operator. Multiple Volume Source DOP microsolvers can be used to perform specific tasks, such as applying sources, sinks, or pumps directly from volumes created in SOPs, instead of relying on DOP specified relationships between objects.
Note
If the 
Smoke Object that the Source Volume operates on has instancing enabled, the sampled volumes are separated based on volumename_instancenumber. The volume name is specified under SOP To DOP Bindings and the current instance number is fetched from the DOP object being processed.
This object should have data associated with it under the name init_cluster. The init_cluster name is unique to every object and is used to fetch the correct volume for sourcing. This data can be generated using the 
Cluster SOP.
If the correct volume is not found, nothing is sourced. If the init_cluster number doesn’t match the correct volume to source from, a different volume might get used.
Parameters
Initialize
Configures the Source Volume microsolver according to the selected preset. Helps clarify and visualize the volume-to-field relationships.
Volume Path
The volume sample location. The specified node should contain the SOP volumes.
Activation
Controls if the source will be applied or not. Mostly useful for liquid sources that can’t be smoothly feathered in or out by controlling the scale source volume.
Scale Source Volume
Controls the scale of the (scalar) volume specified as a source volume to be added to scalar field X.
Scale Temperature
Controls the scale of the (scalar) volume specified as a temperature volume to be added to scalar field Y.
Scale Velocity
Controls the scale of the (vector) volume specified as a velocity volume to be added to vector field X,Y, and Z.
Use Object Transform
Takes into account animated objects.
Volume operation
Source Volume
Controls how to add or blend the SOP source volume on to the specified DOP field.
Temperature Volume
Controls how to add or blend the SOP temperature volume on to the specified DOP field.
Velocity
Controls how to add or blend the SOP velocity volume on to the specified DOP field.
"Blended average" is a very non-realistic pump designed to to make it easy to blend in a desired goal velocity without overshooting or hard-constraint effects. It blends the speed (rather than velocity) of the source velocity with the current fluid velocity. Basically, the node tries to match the speeds of the source and the simulated fluid.
Target Speed
Available when Velocity is "Blended Average". When the fluid is moving faster than this (m/s in in world space), the node will stop adding velocity.
Target Influence
Available when Velocity is "Blended Average". A per-frame normalized value, 0..1, where 0.5 means blend 0.5 times the source speed into the fluid velocity until the target speed is reached.
Max Acceleration
Available when Velocity is "Blended Average". The maximum percentage of Target speed the node can add per frame. After the amount of speed to add has been computed through the Target influence, that delta is then clamped to targetspeed * max_acceleration.
Particle Operation
Source Particles
Add the points from the SOP specified by Volume Path and the point group specified in Source Group.
Source Group
The point group from which to source particles.
Particle Fluid Object
The Particle Fluid Object node for the simulation to be affected.
Source Volume uses this node to obtain information such as fluid particle attributes, parameters from the 
Particle Fluid Object node, etc.
Time Offset Scale
Offset any new particles by adding their scaled velocity multiplied by a random portion of the current timestep. This can help ensure the emitted stream of particles appears regular even at lower simulation substeps.
Time Offset Seed
The seed used to randomly offset the particles by their velocities.
Life Expectancy
If enabled, set the particles' life attribute to control how long the particle will live. If sourcing particles
to the 
FLIP Solver, then Apply POP Solver and Reap Particles must be enabled on the solver
for this attribute to have an effect.
Life Variance
Particles will live the number of seconds in Life Expectancy, plus or minus this number of seconds. Use 0 for no variance.
Kill Inside
Kill any particles within the specified DOP field SDF. If Source Particles is enabled, only particles added in the current timestep are eligible to be killed. If Source Particles is disabled, all particles are eligible to be killed.
Stream Name
Any emitted particles will be placed in this group.
Masks
Field to multiply the sourced volume with. By enabling Absolute only parts of the source volume with a Mask Field value lower then 0 are being considered (but not multiplied).
SOP To DOP Bindings
Volumes
Specifies the SOP volume name to look for. In the case of Temperature and Density this must be a scalar volume, such as X. Velocity must be of a type vector, such as X.X, X.Y, X.Z.
Add To Field
Controls what field to add the sampled volume to. Source and Temperature volumes should be added to a scalar field. Velocity should be added to a vector field.
Instancing
Instancing
When performing clustered simulations it is important that each cluster receives its own individual sources. This is done by affixing the cluster number to the named volume that is sourced.
This option controls if this affixing of source names is performed. Auto-detect will attempt to determine it based on the smoke object’s instancing setting. However, some times one wishes to use the same source across many instances, in which cases this should be overridden to Off.
Clear
Fields to clear
A space-separated list of fields to clear after sourcing operations. Not clearing tempvel or source enables visualizing them later on.
Inputs
First Input
This optional input can be used to control which simulation objects are modified by this node. Any objects connected through this input and which match the Group parameter field will be modified.
If this input is not connected, this node can be used in conjunction with an Apply Data node, or can be used as an input to another data node.
All Other Inputs
If this node has more input connectors, other data nodes can be attached to act as modifiers for the data created by this node.
The specific types of subdata that are meaningful vary from node to
node. Click 
an input connector to see a list of available
data nodes that can be meaningfully attached.
Outputs
First Output
The operation of this output depends on what inputs are connected to this node. If an object stream is input to this node, the output is also an object stream containing the same objects as the input (but with the data from this node attached).
If no object stream is
connected to this node, the output is a data output. This data
output can be connected to an 
Apply Data DOP,
or connected directly to a data input of another data node, to
attach the data from this node to an object or another piece of
data.
Locals
channelname
This DOP node defines a local variable for each channel and parameter on the Data Options page, with the same name as the channel. So for example, the node may have channels for Position (positionx, positiony, positionz) and a parameter for an object name (objectname).
Then there will also be local variables with the names positionx, positiony, positionz, and objectname. These variables will evaluate to the previous value for that parameter.
This previous value is always stored as part of the data attached to the object being processed. This is essentially a shortcut for a dopfield expression like:
dopfield($DOPNET, $OBJID, dataName, "Options", 0, channelname)
If the data does not already exist, then a value of zero or an empty string will be returned.
DATACT
This value is the simulation time (see variable ST) at which the current data was created. This value may not be the same as the current simulation time if this node is modifying existing data, rather than creating new data.
DATACF
This value is the simulation frame (see variable SF) at which the current data was created. This value may not be the same as the current simulation frame if this node is modifying existing data, rather than creating new data.
RELNAME
This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).
In this case, this value is set to the name of the relationship the data to which the data is being attached.
RELOBJIDS
This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).
In this case, this value is set to a string that is a space separated list of the object identifiers for all the Affected Objects of the relationship to which the data is being attached.
RELOBJNAMES
This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).
In this case, this value is set to a string that is a space separated list of the names of all the Affected Objects of the relationship to which the data is being attached.
RELAFFOBJIDS
This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).
In this case, this value is set to a string that is a space separated list of the object identifiers for all the Affector Objects of the relationship to which the data is being attached.
RELAFFOBJNAMES
This value will be set only when data is being attached to a relationship (such as when Constraint Anchor DOP is connected to the second, third, of fourth inputs of a Constraint DOP).
In this case, this value is set to a string that is a space separated list of the names of all the Affector Objects of the relationship to which the data is being attached.
ST
This value is the simulation time for which the node is being evaluated.
This value may not be equal to the current Houdini time
represented by the variable T, depending on the settings of the 
DOP
Network Offset Time and Time Scale
parameters.
This value is guaranteed to have a value of zero at the
start of a simulation, so when testing for the first timestep of a
simulation, it is best to use a test like $ST == 0 rather than
$T == 0 or $FF == 1.
SF
This value is the simulation frame (or more accurately, the simulation time step number) for which the node is being evaluated.
This value may not be equal to the current Houdini frame number
represented by the variable F, depending on the settings of the DOP
Network parameters. Instead, this value is equal to
the simulation time (ST) divided by the simulation timestep size
(TIMESTEP).
TIMESTEP
This value is the size of a simulation timestep. This value is useful to scale values that are expressed in units per second, but are applied on each timestep.
SFPS
This value is the inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.
SNOBJ
This is the number of objects in the simulation. For nodes that
create objects such as the 
Empty Object node,
this value will increase for each object that is evaluated.
A good way to guarantee unique object names is to use an expression
like object_$SNOBJ.
NOBJ
This value is the number of objects that will be evaluated by the current node during this timestep. This value will often be different from SNOBJ, as many nodes do not process all the objects in a simulation.
This value may return 0 if the node does not
process each object sequentially (such as the 
Group
DOP).
OBJ
This value is the index of the specific object being processed by the node. This value will always run from zero to NOBJ-1 in a given timestep. This value does not identify the current object within the simulation like OBJID or OBJNAME, just the object’s position in the current order of processing.
This value is useful for generating a
random number for each object, or simply splitting the objects into
two or more groups to be processed in different ways. This value
will be -1 if the node does not process objects sequentially (such
as the Group DOP).
OBJID
This is the unique object identifier for the object being processed. Every object is assigned an integer value that is unique among all objects in the simulation for all time. Even if an object is deleted, its identifier is never reused.
The object identifier can always be used to uniquely identify a given object. This makes this variable very useful in situations where each object needs to be treated differently. It can be used to produce a unique random number for each object, for example.
This value is also the best way
to look up information on an object using the dopfield expression
function. This value will be -1 if the node does not process objects
sequentially (such as the Group DOP).
ALLOBJIDS
This string contains a space separated list of the unique object identifiers for every object being processed by the current node.
ALLOBJNAMES
This string contains a space separated list of the names of every object being processed by the current node.
OBJCT
This value is the simulation time (see variable ST) at which the current object was created.
Therefore, to check if an object was created
on the current timestep, the expression $ST == $OBJCT should
always be used. This value will be zero if the node does not process
objects sequentially (such as the Group DOP).
OBJCF
This value is the simulation frame (see variable SF) at which the current object was created.
This value is equivalent to using the
dopsttoframe expression on the OBJCT variable. This value will be
zero if the node does not process objects sequentially (such as the
Group DOP).
OBJNAME
This is a string value containing the name of the object being processed.
Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.
The object name can
also be used to treat a number of similar objects (with the same
name) as a virtual group. If there are 20 objects named "myobject",
specifying strcmp($OBJNAME, "myobject") == 0 in the activation field
of a DOP will cause that DOP to operate only on those 20 objects. This
value will be the empty string if the node does not process objects
sequentially (such as the Group DOP).
DOPNET
This is a string value containing the full path of the current DOP Network. This value is most useful in DOP subnet digital assets where you want to know the path to the DOP Network that contains the node.
Note
Most dynamics nodes have local variables with the same names as the
node’s parameters. For example, in a 
Position node,
you could write the expression:
$tx + 0.1
…to make the object move 0.1 units along the X axis at each timestep.
Examples
The following examples include this node.
fieldforce Example for Field Force dynamics node
DensityViscosity Example for FLIP Solver dynamics node
FlipColumn Example for FLIP Solver dynamics node
SpinningFlipCollision Example for FLIP Solver dynamics node
VariableViscosity Example for FLIP Solver dynamics node
EqualizeLiquid Example for Gas Equalize Volume dynamics node
UpresRetime Example for Gas Up Res dynamics node
AdvectByVolume Example for POP Advect by Volumes dynamics node
Open CL smoke Example for Smoke Object dynamics node
ColourAdvect Example for Fluid Source geometry node
CoolLava Example for Fluid Source geometry node
| See also |
