Vellum Sims On Models With Overlapping Pieces

[RyanJP]

I'm struggling to find a good way to sim imported OBJ's that have pieces overlapping (right now I'm using a model of scissors where the blade geometry intersects the handles, hidden from view so it looks good on the surface). My first thought was to just convert to a VDB volume and back again but then I get polygonal geo and running a remesh on that is useless because the resolution is too high. So maybe there's a good node that can lower a mesh resolution and convert it to triangles?

I also tried the Weld constraint but that didn't seem to help either. But it's very possible I'm not doing it correctly.

 

Thanks!

[Midasssilver]

Without seeing your hip file, I can suggest that if you change the Target edge length of the remesh you can change the resolution of the geometry to something lower. Also a Divide Sop with maximum edges set to 3 will triangulate your mesh. If you want additional suggestions, post the hip!

[RyanJP]

Sorry for the delay, got pulled onto other things. Hip attached-

Scissors Test Balloon Fail.hiplc

[RyanJP]

I got the remesh working correctly but the intersecting geometry still freaks out

[Midasssilver]

You need to lock your obj in the hip file you post, or we can't load it.

[RyanJP]

1 minute ago, Midasssilver said:

You need to lock your obj in the hip file you post, or we can't load it.

Ugh sorry my bad. OBJ attached!

Scissors.obj

[Midasssilver]

I'm not 100% sure what you are trying to do with your scene, but I got better results by changing a few things. First, I converted your geometry to a cleaner mesh that supports booleans. I used a boolean operation set to union to delete the overlapping area between pieces of the scissors. When that didn't improve the constraint issue you had, I tried to set up a similar sim just using the vellum solver outside of dops - it seemed to work a lot better. If you need your sim to operate inside of dops for some reason, then the differences between these two setups would be the next thing you resolve.

Scissors Test Balloon Fail_01.hiplc

[RyanJP]

Very cool very cool. I think I can learn a lot from this file, thank you! I just have a couple questions for clarity-

1) The assemble node is taking the broken up geometry and creating packed primitives from it, correct? Essentially splitting all of the unconnected geometry into individual parts?

2) The blast nodes then isolate the geometry into 2 streams

3) Unpack makes the geo editable again

4) Convert from packed to.. polys? Is this standard workflow when working with PP's?

5) The Boole I get, that's a really good idea

6) And then... the CHOP Net. I'm not really understanding the purpose of this.

 

So is creating packed primitives the best way to approach this type of geometry? I'm fairly new to Houdini and I've been spending most of my time learning about the "cool stuff" like liquids. particles. etc. but now is time to get into the nuts and bolts of best practices so I can use it comfortably in production and solve these type of technical problems. I really appreciate you taking the time to help me understand. Again, thanks so much.

 

 

[Midasssilver]

1. The assemble node is creating packed geometry from the separate pieces of the scissors. It makes 4 separate objects (I believe based on the primitive connectivity), which is why you get 1 for each blade and 1 for each handle.

2. Correct. I separate into two streams to that I can perform the boolean operation properly. The divide is to get the mesh triangulated.

3. Unpack brings the full point count back, but I have experienced components being unselectable without being converted to polygons first.

4. I can't tell you if this is standard, but I do it lol. I have noticed that unpacking geometry isn't always enough, especially with surface collisions in DOPs, so converting to poly usually fixes that.

5. Cool.

6.  The chopnet was because I wanted to get some noise on the geometry, but I didn't want to use the noise you added via dops. So instead, I right clicked on the wind parameter in the forces tab of the vellum solver, went to motion FX and selected noise. This animated the wind with a random noise similar to what you were doing in DOPs, but not in dops

[ryew]

14 minutes ago, Midasssilver said:

3. Unpack brings the full point count back, but I have experienced components being unselectable without being converted to polygons first.

4. I can't tell you if this is standard, but I do it lol. I have noticed that unpacking geometry isn't always enough, especially with surface collisions in DOPs, so converting to poly usually fixes that.

+1 on both of these points.  I have made it a habit to use a convert to poly any time I unpack geometry after experiencing inconsistencies with selection when only unpacking geo.  

[RyanJP]

1 hour ago, Midasssilver said:

6.  The chopnet was because I wanted to get some noise on the geometry, but I didn't want to use the noise you added via dops. So instead, I right clicked on the wind parameter in the forces tab of the vellum solver, went to motion FX and selected noise. This animated the wind with a random noise similar to what you were doing in DOPs, but not in dops

Super cool. Never would have thought of that. Need to learn more about CHOPs seems like they can be really helpful/interesting

[Midasssilver]

Yeah, Chops are super powerful and cool, but also pretty convoluted. Wish I was better with them too, but adding a simple preset like noise or a sin wave is super easy to achieve. Lmk if u have any other questions re: your scene if they come up