native Houdini volumes

[ghiom3d]

Hello, on the Vray4houdini page of chaosgroup website we can read :

VOLUME RENDERING

Fast and accurate rendering of native Houdini volumes and OpenVDB caches.


My english isn't 100% accurate, but for me it's mean that i can render fire and smoke like i do in Mantra or redshift. using the bgeo.sc cache files i' usually do not ?

so, i create my fire and smoke with Pyro, i assign a material with Vray-phxShaderSim. in parameter i setup Houdini fire/smoke then i fill the Fields with the correct temperature density etc attributs.

I'm trying to render .. nothing appear.

I check in rendering parameters in OUT context. i see a probabilistic volumetrics, i try to see if if's change something but not.


How to render native Houdini Volumes ? needs help. thanks you.

[ghiom3d]

I'm trying to use vdb cache instead of bgeo.sc .something wrong happend.

[ghiom3d]

it's say only .aur is supported

[ghiom3d]

ok i find, i think.. it's simpler than i was think. i have to find now the good parameters to render the same thing we have in viewport .

[ghiom3d]

physically Based = 0.9 in volume grid fire intensity is a good start.

[chakarov]

Hello ghiom3d , you can use houdini`s native File or FileCache SOPs to load vdbs. VolumeGrid Cache SOP works only with aur files /ChaosGroup Phoenix FD cache files/. Looks like we are forgotten to update the docs page.

[ghiom3d]

thanks you chakarov looks like i can use the bgeo.sc cache right now instead of a vdb sequence.

Physicaly Based set to 0 make it very bright.
Physicaly Based set to 1 make it fully black.

It's like opposite than what i see on documentation. and 1 > flame are black look like a error to me not ?
inb doc we saw that physically 1 make it more bright than 0 and in my case it's inverted.

Nightly from 14/12/19 on H18 18.0.318

[Gosho.Genchev]

Hey, ghiom3d ,

the Physically Based option expects real-world temperature values, so a good start would be to remap the heat or temperature field to values between e.g. 800 and 3000.
For instance, using a Volume Wrangle, you could

f@heat = 800 + fit(@heat, 0, 2, 0, 1200);

This should give you the expected behavior.

We're currently working on adding information guides on major features so such information is readily available.

Cheers!

[ghiom3d]

Hi thanks you Gosho.Genchev . DOn't know if it's the nightly build or i misunderstand something.
I add the volume wrangle node after my cache file. i change heat by flame because it's the name of my attribut in my case.
now it's look thousand times too much bright. so i put physically based at 1 and i see better my fire. but i loose the colors of the flame. it's very long to render, it's not nice.

In the doc, when we change physically based from 0 to 1 , we add a lot of power in the fire. HEre, it's not the case, we have a powerfull fir at 0 and many less one at 1.