Volume: Store vel as one att ( not vel.x,vel.y,vel.z )

[morn66]

Hi everyone,

I want to create a volume that contain a velocity att to my voxel.

I realize that in some situations, vel can be store as one att but sometimes it duplicate it for each axis (vel.x, vel.y, vel.z). I guess it's probably faster to only have vel store one time as a vector attribute.

How can I achieve that for this simple exemple below? Should I use a different node than "volume".

Thanks

 

[morn66]

I have just found out that it is possible to convert vel to a vdb with a "convert vdb" and after use a "vdb vector to merge". Not sure if it's the right thing to do but it works.

If you guys have extra info about that topic, let me know!

Cheers

[char]

Volume SOP creates vel.x, vel.y, vel.z field which is different to what VDB from Particles would create. VDB from particles would only create one field (ex: vel).

In H documentation for VOLUME SOP, there are a couple of things I can quote.

Quote

Stores a vector at each point. This is actually represented using three scalar fields (for example Cd.r, Cd.g, Cd.b) but Houdini knows to treat them as a single volume.

You can use VDB Vector Merge to merge the .x, .y, .z fields into one single VDB field.

Volume SOP (as far as I know), is an old way of creating volumes, now that OpenVDB workflow is around, it's more efficient in terms of resolution and speed. There is an in-depth explanation if you Google "Volume Houdini".

Quote

Because of the way this volume type is represented in memory, it does not require that you specify a box containing the volume; it can extend infinitely. Despite this, a VDB does define a 3D grid of voxels over the whole space.

 

[morn66]

Thanks @char for the explanation!

[morn66]

I found out that: "vdb"node follow by "vdb activate" will create exactly the vel attribute as one. Doesn't need to use the vector merge.