FLIP Low Res To High Res Ocean Workflow

[GlennimusPrime]

Hello Houdini wizards! I'd love to hear from anyone who has blended high and low res flip ocean sims together.

I've been studying Igor's HUG presentation on combining low and high res FLIP surface and vel fields. He goes into quite a bit of depth on the subject, but not quite exactly what's going on inside his attribute transfer vops.

I've built a network following along very closely to what he's done, but I'm not quite getting the correct result with my two yellow vop networks. These are supposed to blend the edges of the high res surface and vel fields into the low res fields.

If anyone has tried a similar approach to what Igor is showing us here, I'd love to hear your thoughts!

.hip file attached of where I'm up to in this difficult process.

..and to help out, I've also uploaded the high and low res cache frames so you don't need to export a cache.
You can either grab the full cache, or just a single frame from the middle of the sim. Both caches can be downloaded here

blend_low_high.hipnc

[Atom]

I played around with that and got some help on a Discord. It's hard to see in the video, but inside the VOP blending the @vel, there are two types of volume samples. The top one is a volumesamplev (used to sample vectors such as velocity) and the bottom one is a volumesample (used to sample floats such as density).

Try swapping your top volumesample node with a volumesamplev.

Edited May 25, 2023 by Atom

[CeeGee]

Maybe this can help
Blend surface
- what i am doing is sample from low mesh position with attribut trasnfer on high res mesh, and then using bbox of high res sim domain, converting to volume, and finaly using it ask maks, then blending low_P and original high res P with that volume maks, so that high res mesh P blend into low res P and edges are matching|
- then converting back to vdb and using as surface field for wwater or layer on for meshing

Blend vel
- same idea like surface
- resample low res vel to match high res vel, bring them both into vop, with same maks, and just blend then like surf field, and export as new vel

Thats all, its very simple idea, it was more to make something working for my tests

Hope this help

[Atom]

That does help, but I'm still playing around with the OP's hip file and can't seem to eliminate the edge. What input min/max values are you using inside the FIT nodes? I assume the fit remaps to 0-1 to drive the ramps?

Edited May 25, 2023 by Atom

[CeeGee]

Hi,

In his scene there was few problems with vdb operation, attribute transfer stuff.
His scene is very small, i meen upres region is close to same low res sim, so it can be tricky to blend all edges.
This is fixed version

blend_low_high_02.hipnc

Edited May 25, 2023 by CeeGee

[GlennimusPrime]

10 hours ago, CeeGee said:

Blend vel
- same idea like surface
- resample low res vel to match high res vel, bring them both into vop, with same maks, and just blend then like surf field, and export as new vel

Thanks so much @CeeGee for the help in adjusting the surface field. So great to hear from the man himself!

I appreciate the images of your vop networks too, however I'm still having difficulty with blending the vel.
I'm using a volume trail to visualise the vel field after blending the high and low res fields, but the vop net doesn't seem to be making any changes to the vel field?

It doesn't look like there is any blending working here at all. I have the vop net setup the same as your example image.

[CeeGee]

here is fixed version, one of main problems in your scene is that your bound that you use for cuting fields is not matching your cache sim domin, you need to think about that
every sim first have small reseed boundry most of time 0.5, you need to remove that before doing any combine, and also when you are doing wwater sims

blend_low_high_03.hipnc

[GlennimusPrime]

15 hours ago, CeeGee said:

here is fixed version, one of main problems in your scene is that your bound that you use for cuting fields is not matching your cache sim domin, you need to think about that
every sim first have small reseed boundry most of time 0.5, you need to remove that before doing any combine, and also when you are doing wwater sims

Right, ok! This makes more sense. Thank's so much for this Igor, this is a huge help in understanding this workflow a lot better.

I'm sure this will be a valuable thread for the community to follow too.

 

- Glenn