[RESOLVED] Separating every points that moved at least once

[Marinc]

Hi ! 

I'm currently working on a vellum grain simulation for snow. I need to export it to Maya for the rendering process! (our light rig and texturing is made on Maya) 

So my idea was to separate my meshing in two parts:

• one will be particles that moved at least one time (the real "grains") aka a dense meshing to get grains almost individually

• the other will be the particles that did not move/are less important aka lighter meshing to get the shape of the grains.

in these way, for big scenes, I'll have a two alembic low & high, instead of one very heavy alembic file.

Problem is : I can't seems to find a way to separate the two of them. 

I saved my simulation (cache) with P and V , and wanted to create a group that'll update at every frames to put the new points that moved in it. Unfortunately: Houdini is overreding the group, like it's creating a new one for every frame. 

Any idea what I can do ?  

 

Thank you so much, 

Marine 

 

PS : On the file I attached, the idea is to get everything around the foot shape in red

Edited June 1, 2020 by Marinc
resolved !

[skomdra]

Maybe use a timeshift node and transfer velocities on the first frame of the sim, make a group by velocity and transfer the group to the moving points after? 

Though I don't see why wouldn't you select part of the sim with the group node, group by bound to select part of the sim which you already know it is more important for the final output? You can even animate bound if you need it to follow the steps and update it based on another sop which is in the second input, etc. 

Edited June 1, 2020 by skomdra
more ideas

[Marinc]

Thank you !
Well I didn't though of your second solution, so I tried it , but once more, Houdini override the group at every frame.

Gonna try to combine it with the first solution ! (i'm sorry, still a novice in Houdini, I've got a lot to learn ! )

 

[skomdra]

I have to check exactly what you want to do, maybe make a small prototype and upload a hip file? But if you need it to update during time, then I think you would need to use a sop solver, which I am not very familiar with but it seems very simple to setup. 

[Marinc]

Well ! After looking for solutions, we finally found something that worked !

I'm taking the first and last frame with a time switch (freeze) , then I'm comparing the p value (with a threeshold) via a point wrangle and I can select the falloff of my "velocity" ! It's working like a charm !

Thank you so much for your help !!