Clouds: What is going with density, position and volumesamplefile?

[anicg 12]

Here are two simple volume noise set ups:
1. One uses position, but needs a volumesamplefile
2. The other uses both position and density and doesn't need a volumesamplefile
Both give results, different results.

if I however start messing with combinations using the volumesamplefile I get this:
3. position_without_volumesamplefile
4. position_and_density_with_volumesamplefile

Any idea what the real role of the volumesamplefile and its relation with the position and density?

[flcc 146]

The volumeamplefile is mainly used to retrieve values from another stream,
such as you want to make a boolean opreation between two vdb, or use the vdbanalysis node.
It just get any kind of value (Cd, gradient, density etc..) at a given position

In your example the volumesamplefile node is not necessary.
Just subtract aanoise (3D input, 1D noise) result to density (wich is a simple float value). Don't forget a fit node with aanoise.
No reason to add or multiply density with position (vector), unless you want an attenuation according to the distance to the center.

Another reason to use volumesamplefile in place of input P is when your volume vop is in a solver.
Don't really know why, I'm also curious to know.
 

Edited May 6, 2020 by flcc

[anim 1,262]

volumesamplefile() allows you to get density at another position than the psition of the current voxel

so if you add vector to position, you can reach voxel value from that offset/displaced location, so essentially adding vector noise to P and sampling volume density at that location will displace the input volume

 if you just bind the @density directly, that will give you density value of a current voxel (same as volumesample at current P), if you multiply it by noise value you will just mask the density