vdb mesh culling?

[microdot]

Hello All,

 

Is there a way to cull a vdb mesh applied to particles?

For example, if you have a basic flip tank, but only want to mesh the top portion , etc.

 

 

[JonathanGranskg]

Yes, when you convert it to polygons you can plug another vdb into the third input to mask out the areas you want to keep/delete. 

 

The vdbcombine node can also be used to do boolean operators on vdbs. Although, this does not achieve the effect you are asking for. Hope it helps!

[microdot]

Ah, makes sense, I'll try that out.

thanks!

[pbarua]

You can use reference VDB to activate from. Simply wire VDB by which you want to mask (like camera or clipping box) to second input of VDBactivate and set it to reference.

[microdot]

Thanks guys.

 

I'm noobin' it up. Is this close?

Sad I know, heh.

 

I know something must be missing since mesh disappears, but not sure what.

Edited April 29, 2015 by microdot

[LukeLetellier]

I prefer to do this in an attributeVop after it's been meshed. Place a "remove point" node inside an If/Then block, and make a condition like "If ty <  -.1" then all the points with a y value below that will be removed. If you're doing an ocean shot, and need to trim right/left/front/back edges as well, you can use a similar technique. The operation is pretty quick. 

 

Also be sure to wire the ptnum value into the if/then block, and hook it up to the remove point node. 

Edited April 29, 2015 by LukeLetellier

[microdot]

Ah, I have not yet ventured into the VOP world, but thanks for the solution.

I will have to figure that one out and try it.

[microdot]

I ended up using the third input mask technique with a box, since I'm using it to test settings before output.

Easiest way for me, but I'm going to try out the other tricks as well, to understand them better.

Thanks again guys.

[microdot]

Another question, how would I employ the same technique but with mask applied to the cached particles,

so its only calculating that section for faster mesh tests? Is that possible?

 

Thanks.

[dpap]

You can use reference VDB to activate from. Simply wire VDB by which you want to mask (like camera or clipping box) to second input of VDBactivate and set it to reference.

 

 

Anyone kind enough to make an example using this method? It is a bit  embarrassing but  I didn't manage to make it work either.

 

Thanks.

 

Edit: Never mind, I got it.

Edited May 7, 2015 by dpap

[BOON]

Maybe I did not understand your question fully, but why not just delete by expression $TY<1?

Or group with bounding object and delete grouped points?

Or color transfer attribute from geo and delete $CR==1?

 

Since points get deleted before the meshing process, there is no unnecessary calculation for those unwanted points.

[microdot]

Cool thanks. Yeah I'm super new to Houdini so didn't even know those were options.

 

The input mask works well, but I noticed if I turn it off it draws the full mush very quickly, making me wonder if its calculating the full cache, and then masking afterward.

 

Will def check out those tips, thanks.

[dpap]

 

Or group with bounding object and delete grouped points?

 

Since points get deleted before the meshing process, there is no unnecessary calculation for those unwanted points.

 

 

I realised afterwards that there's a better way but when I came back to repost I realised Boon spotted it first  

 

Here's an example

Selective Particle Meshing.hip

[BOON]

Here's another example of multiple ways to cull points before meshing.

delete_points.hipnc

[microdot]

wow, cool. Nice techniques.

The fact that I even start to understand some of whats happening in the nodes is amazing heh.

 

Not the initial question, but just out of curiosity, with the point delete method if you wanted to animate the mask object to reveal the inverse mesh, that wouldn't work right?

Edited May 7, 2015 by microdot

[BOON]

Might this be what you're looking for?

I'm not totally sure what are you trying to achieve, but animating mask object to delete points should be doable.

delete_points_animated.hipnc

[microdot]

Ah, I'm guessing I can't open these since I'm only using the apprentice version?

 

I'm playing with the delete points version based on the pic, but not sure how to set the bounding object.

 

 -Also dumb question, not that I've cached the sim as a .bgeo, is it seen as particles or geo?

I assume particles since vdbfromparticlefluid still worked?

Edited May 11, 2015 by microdot

[BOON]

I'm playing with the delete points version based on the pic, but not sure how to set the bounding object.

1. plug a bounding geo into the 2nd input of a group node.

2. on the group node, go to bounding tab > enable > bounding object. Make sure to specify primitive / points selection.

 

 

 -Also dumb question, not that I've cached the sim as a .bgeo, is it seen as particles or geo?

I assume particles since vdbfromparticlefluid still worked?

You can cache practically everything as .bgeo format, as long as they belong to the sops level.

[microdot]

Very cool, thanks!