Hi!

I have a point cloud with a v@v value on each point. My goal is to create a vector field that represents the curl of this point cloud.

I figured that, in order to do this, I'd need to rasterize the point cloud into a volume and then use this cool setup [www.sidefx.com] to compute the curl.

However, when I use the volumerasterizeattributesnode, I can only create a single velocity volume (apparently?). The compute curl setup requires the volumes vel.x, vel.y, and vel.z. I'm sure there's a hundred ways to get these three volumes from a point cloud, but I haven't been able to figure it out yet.

One thing I've tried is to creating a volume with the volumenode with each vel.x, vel.y, and vel.z.



I've then tried to use a volumerasterizepointsnode to pull each component of the velocity from the points into the respective volume, but they don't seem to be copied over.

Maybe I'm overthinking this or missing something really simple?

Thanks!
Anson

After Volume Rasterize Attributes, try using a VDB Vector Split node.

Tanto
After Volume Rasterize Attributes, try using a VDB Vector Split node.

Interesting!

Hey, this worked! Interestingly, I had to convert the VDB back into a Volume... Not sure why, but it did the job!

Another workaround I found (although this is slower) is to copy to a new volume using a volume wrangle:

AnsonSavage

Tanto
After Volume Rasterize Attributes, try using a VDB Vector Split node.

Interesting!

Hey, this worked! Interestingly, I had to convert the VDB back into a Volume... Not sure why, but it did the job!

Another workaround I found (although this is slower) is to copy to a new volume using a volume wrangle:

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Actually, the two approaches produce different results for the curl field... Still trying to determine exactly what the difference is...

AnsonSavage
Interestingly, I had to convert the VDB back into a Volume... Not sure why, but it did the job!

because Volume Analysis SOP works on Houdini Volumes, not VDB

but you can directly use VDB Analysis which has Curl mode
so essentially you should be able to just use Volume Rasterize Attributes + VDB Analysis, with no channel splitting required