Source Volume DOP - 2 Questions

[catchyid]

Hi,

Plz see attached images.

1- The DOP Source Volume has three parameters: Source, Temperature, and Velocity. what does "Source" refer to in the corresponding SOP volume? Meaning, "Temperature" would be read from "temperature" scalar field of the input SOP volume (see green arrow on left panel), same applies on Velocity (i.e. it's defined as vel in SOP Volume), both parameters are well defined, but what does "Source" here refers to? Is it density, and if so, is this always the case? 

2- What is the difference between "Volume Operation" and "SOP To DOP Bindings"? My initial guess is that "Volume Operation" does the mixing between the current fields and the fields imported from the Volume SOP (e.g. Copy, Add,...), and "SOP to DOP Binding" is another layer to shuffle the output, i.e. one can copy "density" to "temperature" and vice versa? Is that correct? What confuses me is the world "Add to Field" which is used in "SOP to DOP Binding" which indicates that the result is always added to the field (i.e. it will always Add SOP density to current DOP density)

Thanks,

 

[LaidlawFX]

You pretty much answered your own questions. 

http://www.sidefx.com/docs/houdini/dyno/fluid_sourcing

http://www.sidefx.com/docs/houdini/nodes/dop/sourcevolume

The way I learned was to just try all the different shelf options, example files and odforce examples, and compare the results, but if you read up on the help docs they go a lot further now a days.

For the source, it is the density volume in your case, but this is generally dependent on how the dop source volume is initialized with different presets and shelf tools, or different workflows. This can be completely changed however depending on your simulation, and how it is be remapped. Your screen grabs point out the connecting hierarchy of where density is being defined as the source volume under the SOP to DOP Bindings. So it is best to check that mapping until you get used to the different combinations. 

 

For the bindings from the docs:

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.

 

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.