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sasbom

Intersection between volume and polygon terrain?

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Hey everyone,

I'm starting my houdini journey because the company I'm going to intern at in the summer does a lot of houdini stuff.
I don't want to be left in the dark, so I'm studying on my own for now.

When I was at the company in question, last time, someone showed me a way to use a volume from a mesh (he used the test_rubbertoy geo) to get a
intersection plane without using boolean. I remember he used some wranglers, and ended up with a grid with color data which he used to delete the unnessecary parts outside the colored intersection area.
Then he somehow turned the mesh into a isosurface, to smooth it out.

I've been trying this for some time now and I can't for the life of me figure out how he did it. 

I've had two nearly succesful attempts, one where I used the Intersection Analysis to get the intersection between a grid and the (rubbertoy -> vdb -> vdb to poly (to fuse seperate meshes together)),
then filled the edges I got from that, and then remeshed, which admittedly gets me at least a flat intersection plane. One major problem is that this approach makes the normals of the resulting mesh flip upside down randomly
everytime I move the intersecting mesh, which is a pain if you'd want to use it for particles or something. I tried using a wrangle to copy the point normals of the nearest points to the points of the remesh, but I haven't had much luck with that.
The other thing is that since the Intersection Analysis only returns edges, the shape of the surface is not taken into account, above method only returns planes and distorted planes on surfaces.

The other one I used a attribute transfer with a (mesh -> vdb fog -> wrangle to fit density to 1 everywhere -> scatter -> color {1,0,0}) to project red points from the point cloud to a grid surface, which works, but VERY slowly.
one bonus with this technique is that you can blur the resulting "intersection" but its way too slow.

So, what I've been thinking is this: A VBD is basically a point cloud, so there needs to be a way to compare mesh points to the points in the volume, and assign a color to those points that are close to points on the geo.
I remember said someone doing something like that with a pcopen, but I don't really understand how. I think I get the method, but if someone knows something better, please say so.
I've been struggling with this for a couple of weeks now.

I strive to be more than a shelf tool user, at the least.

Thanks in advance,

sasbom

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Hate to bump into my own thread, but I ended up searching for the "attribute from volume" node.
Appearantly, VDB only has a "outer" shell of particles most of the time, so I was looking for a Isooffset instead of a VDB.

http://www.entagma.com/quicktip-signed-distance-outlines/

I'm glad entagma made a tutorial on it.

Just leaving the message for people having the same problem.

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