about volumes

[mcflait]

Hi juanjo,
i am pretty new using octane, and i am learning how to use octane to render some volumetrics stuff, i saw this post: viewtopic.php?f=102&t=52340&hilit=density, really interesting things there, thanks a lot, could you share some tips, or some steps to keep on mind to get nice render volumes.

Here a test and some questions:
For example, here my first explosion test using octane render, but the main problem is that i can not get the same look that using mantra, i mean my renders using octane lose all the details from my explosion as you can see in the viewport, i decrease the step size and looks better but now the smoke looks completely black, how can i change the density color and the sahdow density like mantra?
And another thing is about the ipr renders, i fo not know why looks like wrong aspect ratio or something like that compared with the camera view from the houdini viewport.


Would be nice to see some hip example from you.
Thanks a lot.

[juanjgon]

Can you share this scene to play with it? It is true that currently the volumetrics shading has some limitations in Octane, but the team is working in a ramp shader for the volume objects that should help a lot with the shading.

The IPR issue can be that you have two or more cameras in the scene, but the camera used for the IPR is the default one (/obj/cam1). You must set the camera to be used for render and for the IPR in the Octane ROP node.

-Juanjo

[mcflait]

Hi Juanjo, i tried to upload the scene, but unfortunately the explosion volume cache size is so huge, anyway... step by step i am understand how works octane for volumes, here a couple of pics.

[haze]

The volume shader ramps will be released in the next alpha. Once the fundamentals of volume rendering is fully finalised, I hope to write a tutorial on some best practices for rendering volumes with Octane standalone. One particular tip that I always need to keep in mind is that you should try to minimise the density of the volume ("scale" in the medium). For example, set the scattering and absorption colours to white, and reduce the density until you can see some detail in the volume. At this point, reduce the volume step length until you get more detail. Without changing the colours and scale, you then need to find the right balance between step length, appearance and of course performance.

I hope this helps a little bit, stay tuned for more info.

[mcflait]

Awesome!! Thanks a lot for the tips haze, really useful!
Here some pics using your tips.
Using White Color in Medium Scattering and scele to 10 for "test1.jpeg" and 100 for "test2.jpeg"

Nice to hear about the ramp color for the density in the next built, would be nice aswell to get a shadow density parameter , and a ramp to blend the transition between the temperature and the density.

[haze]

There will be independent ramps for absorption, scattering and emission. At the moment the only way to tweak the shadows is by modifying the medium scale (viz. density). You can tweak the object visibility using an object layer, but it might impact performance too much to keep track of a separate transmittance for shadows alone. Can you give me more detail on how you would use this?

I'm not sure what you mean by temperature to density blending - right now, for voxels with higher density, output emission is higher (increases linearly). Would the ramp on emission colour be what you were looking for, or did you mean something else?

[mcflait]

Hi Haze, Thanks a lot for your reply.
well, still my main problem, is about what the scattering and the absorption parameters exactly does, would be nice to get a quick brief about how the octane volumes works.
Sometimes is hard to get control about the smoke for example, because i can find any parameter directly connected to the density or density color or something like that.
Finally i can share my scene, a Single bgeo and hip file attached here.
https://dl.dropboxusercontent.com/u/303 ... losion.rar
Would be nice to get your feedback about the volume shading, to control all the fields (density, temperature) how to integrate the heat field to the shading, change the density color....
Thanks a lot for your help.

[lordpazuzu]

There will be independent ramps for absorption, scattering and emission. At the moment the only way to tweak the shadows is by modifying the medium scale (viz. density). You can tweak the object visibility using an object layer, but it might impact performance too much to keep track of a separate transmittance for shadows alone. Can you give me more detail on how you would use this?

I'm not sure what you mean by temperature to density blending - right now, for voxels with higher density, output emission is higher (increases linearly). Would the ramp on emission colour be what you were looking for, or did you mean something else?

About the "temperature to density blending", its more like you break the contribution of emission in two fields, the density aka alpha, and the color driving, so for example you use the heat as a coverage field and the temperature to drive just the color, this way you have even more control but sometimes a bit hard to control, but its all about getting more control for custom shading stuff; So in few words it will be nice to have a two fields approach for the emission contribution, one for the coverage (density), other for the color.

Also it will be nice to have field control in shading (I know that right now Octane can't sample attributes nor primitives form sops) or in the object parameters, not just field scaling but also a non-clamp fit range approach. This way you don't have to modified your fields in sops for a nice shading results, which its very slow with very high resolution primitives.

Thank you!

Alejandro

[haze]

I think I understand what you mean now - at the moment, the absorption grid is actually used as the particle density grid, when it comes to scattering and emission.

I'll take a look at the volume soon