Giving imported geometry from Maya output groups

[eirik.m]

Hello friends!

I have a project going and I have this building to collapse. I made my geometry in Maya, and grouped them in respective groups (in houdini it became 4 subnets). I'm going to take this structure into a glue solver, glue it together and simulate it. But when I direct my SOP path from the Glue solver to the geometry it will not collide with my collision object. Do I need to give each object an output group? I guess the groups from Maya doesn't count And if so, were do I do this? I had this test structure, were I made the geometry in a SOP net inside the autoDopNetwork, and gave each "floor" an output group from the copy node, but this time the geo comes from another package. So how do I do the same with the one made in houdini with the imported one ?

Thank you for your time

- Eirik

[old school]

Here's hoping you used the RBD Glue Tool from the shelf to set stuff up...

If you did that, then you "should" have all your pieces coming in as separate RBD objects. Open the details view / spreadsheet while in DOPs and see if you indeed have all your RBD objects constructed. If not, go back to SOPs and make sure that each piece coming from Maya is "manifold". Manifold means water-tight or all faces on each piece have shared points (I know Maya'ites always call these vertices or verts and I really wish Alias got it right in the late 1980's and called them points but eh, whatever) and no open holes / missing polys plus no self-intersecting polys.

You can achieve this manually with the Assemble SOP which really is an asset wrapper on top of the Connectivity SOP (creates a unique attribute for each group of prims with shared points) and Partition SOP (which creates groups from an attribute).

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If you have all your RBD pieces in to DOPs and they are all manifold, then it's the collision SDF volume representations that aren't being constructed properly. Either the geometry has complex surface features causing the sdf generator to fail (try enabling laser scan) or the geometry is quite large/small where you need to adjust the Divisions. On the RBD Glue Object DOP, in the Collisions > Volume tab, enable "Show Collision Guide Geometry". The collision SDF volumes should show up as red iso-surfaces. If not, there's your problem.

The Houdini RBD solver by default collides points against these SDF volumes. If the volumes are not formed correctly, you don't get collisions.

You "can" disable "Volume Based Collision Detection" and use the geometry thin-plate collider to see how it performs. Still having proper SDF collision volumes is the way to go with Houdini's RBD solver.

[Nik S]

Whenever I work with RBD sims in Houdini I usually make sure that I have proxy geometry for high res pieces coming from maya. Our definition of Proxy Geometry is as follows:

"A single piece of polygon geometry that is built around, as tight as possible, the high resolution asset. Additionally we require that the proxy geometry be a closed surface."

Additionally try using a good old "Ground Plane Object" if your floor is a plane, if non uniform geo, try feeding the ground geo into a "Terrain Object".

If your pieces are moving too quickly the solver may "miss" the collisions in which case you should set substeps on RBD Solver and DOP node higher (generally 5 is good start). Also bump up collision passes in the RBD solver.

Soon there will be Houdini 12! Bullet Solver doesn't care about Signed Distance Fields!

when bringing the proxy geo back into maya either wrap deform the high res onto it or else (if wrap is too slow) you can use some Python magic to create Rivets on all the high res geo then Parent Constrain the High res to the Proxy.

Hope this helps,

- N

Edited November 2, 2011 by Nik S