OTOY Forums

How do you get emission to work? I have a volume with density, heat, temperature and vel grids. I have tried rendering it natively as well as tried to write out an openVDB file. i only seem to be able to render the density... I'll link my VDB file and attach screenshots of my settings.

Im working in Houdini 15.0.347 in windows 10 x64 if that helps any.

https://www.dropbox.com/s/vxj2p5b5kn7a5 ... 8.vdb?dl=0 its 226 megs.

I have tried both the heat and temperature fields and get no change, I've also tried changing the absorption and scattering settings and I still get no emission.

What am I missing?

Thanks for any assistance in advance!

The problem can be the volume material: too strong absorption, low scattering, low emission power, or also the scale of the grid values. Attached you have a scene using your volume that seems to work fine, check it to know how to configure the volume material and the volume settings in the OBJ node.

-Juanjo

First of all thank you so much for the assist!! I've attached two renders after I tweaked a few settings. I changed the volume step length from 4 to 1 so to sample the voxels more to up the opacity. I also changed the absorption and scattering. I changed from a white sphere ENV light to a dusky sun lit scene to get some shadowing on the smoke plumes. I noticed after doing this that I got weird artifacting at the top and in various spots, see attached image suffixed with _temperature. I switched to the heat field instead for emission and I get the other attached render that was MUCH better in terms of artifacting. The last issue I saw was at the top of the volume there is an odd line I'm assuming where the BBOX is. Is there a way around these issues currently? if there is anything I could provide to assist with any of this stuff by the way I'd love to pitch in!!

ALSO, Is there a way to sample the fields and remap values arbitrarily? I've attached two more images where I have rendered the emission texture with your base blackbody and then with an emission texture(purple one). Why does the blackbody have a heavily weighted response curve to it and not the textured one(purple)? Is there a way I can adjust this myself?

Thanks again for all the help, LOVIN this volume rendering situation!!!

ptunstall wrote:First of all thank you so much for the assist!! I've attached two renders after I tweaked a few settings. I changed the volume step length from 4 to 1 so to sample the voxels more to up the opacity. I also changed the absorption and scattering. I changed from a white sphere ENV light to a dusky sun lit scene to get some shadowing on the smoke plumes. I noticed after doing this that I got weird artifacting at the top and in various spots, see attached image suffixed with _temperature. I switched to the heat field instead for emission and I get the other attached render that was MUCH better in terms of artifacting. The last issue I saw was at the top of the volume there is an odd line I'm assuming where the BBOX is. Is there a way around these issues currently? if there is anything I could provide to assist with any of this stuff by the way I'd love to pitch in!!

Can you send to me these scenes (with the volume file, if you are using an OpenVDB file) to the test them here?

The top line seems something that is there in the volume data.

-Juanjo

ptunstall wrote:ALSO, Is there a way to sample the fields and remap values arbitrarily? I've attached two more images where I have rendered the emission texture with your base blackbody and then with an emission texture(purple one). Why does the blackbody have a heavily weighted response curve to it and not the textured one(purple)? Is there a way I can adjust this myself?

A ramp shader for volumes is under development. This feature should help with volume shading.

This is how emission is working now:

"Volumetric Emission Modes
For emission, the Medium node can have either a blackbody emission node, or a texture emission node.

When using the blackbody emission node, it is important to ensure that the data used for the emission grid (see import preferences) contains temperatures in Kelvin. It is common to find VDBs that have unitless "temperatures" with arbitrary ranges such as 0 to 1, or even 0 to 45, as is the case with some sample VDBs from openvdb.org. Typical temperature values range between 0 to 6500, where lower values tend towards longer wavelengths (red colours) and higher values tend towards blue/white. In order to get realistic results from the blackbody emission for volumes, you must disable Normalize in the emission node. Lower temperatures give off less light than higher temperatures, but when normalized, the radiance emitted by all temperatures are equal.

When using the texture emission node, the input temperature grid is interpreted as emission power, not emission temperature. This is more linear in that the higher the "temperature" value, the more light will be given off at that point. Once volume gradients are implemented, you will be able to control the colour (of eg a flame) more precisely. "


-Juanjo

juanjgon wrote:

ptunstall wrote:First of all thank you so much for the assist!! I've attached two renders after I tweaked a few settings. I changed the volume step length from 4 to 1 so to sample the voxels more to up the opacity. I also changed the absorption and scattering. I changed from a white sphere ENV light to a dusky sun lit scene to get some shadowing on the smoke plumes. I noticed after doing this that I got weird artifacting at the top and in various spots, see attached image suffixed with _temperature. I switched to the heat field instead for emission and I get the other attached render that was MUCH better in terms of artifacting. The last issue I saw was at the top of the volume there is an odd line I'm assuming where the BBOX is. Is there a way around these issues currently? if there is anything I could provide to assist with any of this stuff by the way I'd love to pitch in!!

Can you send to me these scenes (with the volume file, if you are using an OpenVDB file) to the test them here?

The top line seems something that is there in the volume data.

-Juanjo

I've attached the modified .hip file. Use the same vdb file as before. Thanks so much!

To avoid the rendering artifacts and match the OpenVDB native rendering, you must enable the "Split Disjoint Volumes" option in the ConvertVDB SOP node. Anyway to render OpenVDB files I think that it is better to use the native Octane OpenVDB file loader.

-Juanjo

Champ status!!!!!! Thanks so much!!!

Hello and regards!

What exactly is the process for getting a VDB file to show in the Octane IPR?


For example, I imported in a cube VDB through the Houdini UI, and then when rendered it shows nothing. Then in the OpenVDB pane I loaded in a Torus. In the IPR I only see the Torus.
What happens to the cube in the IPR, does the imported object in the Houdini UI only act as the 'placeholder' for an external VDB to then be loaded in?

Thanks!