Vector Displacement on Cap mode vs Ocean mode

[andrezaguayo]

Hello everyone, I am pretty new to water simulation and and very happy to be learning. So far Phoenix has been giving me really amazing results.

We recently got a job where we have a lot of large boats in the ocean which we have to simulate. I have seen on other posts that the current best way to mix multiple simulations on the ocean is to have one simulation on ocean mode, and then the others on cap mode, then comp them together. For the most part I am getting that process to work except for one problem with the displacement detail not matching up exactly. When I render a Phoenix sim as Cap the displacement does not look the same as when I render it on Ocean. It feels like the displacement on the Cap is not subdividing as much as it is when on Ocean mode. So when I comp two different sims together you can see a clear difference in how the water looks. Does anyone know the proper settings for getting them to look the same? I have attached an image showing the same exact simulation just the top half is on Cap mode and the bottom on Ocean mode. Thanks in advanced for the help.

[Ivaylo Katev]

your observation is correct, the mesh subdividing arose as solution for some horizon issues, in order to avoid the sudden change of the lod, the subdivision is applied over the entire mesh, affecting the simulation area too.
the cap mode has no subdividing and looks smoother.
however, even if we fix this, you will hit the next issue, when the displaced ocean goes above the water in the simulator. here in your image this is not present, but it will appear in animation for sure.
in general, this technique does not allow to have close up shots of the ships rendered in cap mode, only the one who holds the ocean can be rendered in closeup. we are planing to add a mode for multiple ships, but this can't be expected in the nearest 2-3 months. perhaps you have to render all the ships that have closeup view separately and to blend the sequences in post.

[andrezaguayo]

Ivaylo thank you for the response! That sounds good we will definitely be able to make it work, most of our ships will be small with the exception of two hero ships. I am not 100% following you when you say "however, even if we fix this, you will hit the next issue, when the displaced ocean goes above the water in the simulator." What is the difference between when the ocean subdivides and when the cap mesh does? Would it be a bad idea to do this, turn off displacement in the sim, add a VrayDisplacementMod modifier on top of the cap and plug in the OceanTex. On my initial test it seemed to line up almost perfectly to the other Ocean I am rendering out when testing it out.

Thanks!

[Ivaylo Katev]

i mean when you use cap mode and the ocean extension of another simulator, the ocean is present even in the simulator area, this may cause z-fight or the simulator surface to be hidden behind the ocean surface
this can't happen when the ocean extension is owned by the simulator, because the ocean extension is built with a hole corresponding to the simulator size, and there is a special algo that connects them both with a seam.
btw as i see you are using the grid core, better ask for nightly builds access and use the flip. for the small ships there is no big difference, but for the close up views it's much better. see the attachments to compare them

[andrezaguayo]

Hey Ivaylo thanks for the response again. Thanks so much for the video examples if the grid vs. the flip solver I would love to try out the new solver. Excuse my ignorance, but how do you request access to the nightly builds?
EDIT: I think I just requested for nightly builds. Where can I find more information about all the new features?

[Ivaylo Katev]

you have to write to support@.... , they will explain you the details and will provide the access

[andrezaguayo]

Thanks Ivaylo, I am excited to try it out. Does the flip solver have any other benefits besides a smoother and better result. Is it faster to simulate or smaller cache files?

[Ivaylo Katev]

well, i didn't say smoother, it's not smoother, it's just better. about the simulation time - you can't compare them directly, the flip deals with particles the grid deals with cells. for equal count particles - cells they have similar speed, but the grid simulator requires higher spf , that makes it in fact slower.

[andrezaguayo]

Hey sorry I am asking you questions on two threads, but I wanted to keep related questions together. I just got the nightly builds installed and am messing around. I was wondering if I could ask more about the flip solver? I feel dumb but how do I enable the flip solver vs. the original grid solver? Is it automatically using the flip solver if you have liquid check on? Thanks

[Ivaylo Katev]

when you select to simulate liquid it's automatically enabled. the manual choice between flip/grid solver is in the advection method, technically the flip solver uses particles to keep the fluid properties and it's a kind of advection method. the conservation method is always smooth-direct, the conservation option is ignored. in few weeks we will separate the UI, currently we share the UI for the grid and flip solver, that is a bit complicating the users life

[andrezaguayo]

Hey Ivaylo, how safe would you say pushing the nightly builds in the production is? So far I am loving the results if the sims I at testing, but was having a few random problems. I want to use these new sims I am testing but am worried even more problems will arise because it is still being developed. Are the nightly builds not intended for production and just testing? Thanks.

[Ivaylo Katev]

you can use nightlies in production, some scenes in got 5 are made with very early version of the flip solver. of course they are less reliable, but if your setup works, the hidden bugs are not a danger, beside this we can fix any problem that you report in a day, that is impossible for official release. the main problem with the nightlies is that is possible the behavior to l be changed. we try to keep compatibility even with the scenes made with nightly builds, but sometimes just the simulation result is not similar, because change in the core.