Working with glass and liquid.

[Voidmonster]

As part of my ongoing process of learning to use Octane, I'm working with glass that contains liquids.

Specifically I wanted to know what the correct modeling techniques are with Octane.

The correct technique in Maxwell Render involves a slightly non-intuitive physical construction -- the glass part is only double-walled up to the point where the liquid is contained, and a thin meniscus layer separates the gapless volume of liquid, so the liquid is fully contained and also acts as the interior wall of the glass.

There are some very nice diagrams, but I didn't make them and I don't want to link to images on the Maxwell forums.

This technique did not really work well for me in Octane.

There are a handful of things I noticed between the two renders. Foremost, I did not accurately match the scenes for camera layout. I just eyeballed position and FOV, so that's slightly off, as well as the rotation of the HDRI. I didn't try very hard to match up the material on the ground plane for anything but color. I think I forgot and inverted the specular texture in either Octane or Maxwell, which might account for the differences. It's otherwise the same model and texture maps.

In the Octane render, I notice that the glass doesn't appear double-walled where it 'contains' liquid. It looks exactly like what it is, a solid chunk of glass with a different material inside it -- there is no interreflection between the liquid and the glass.

Also, it looks like somewhere between Lightwave and Octane some precision was lost on positioning. The glass is sitting about 0.2mm above the ground plane, but in the render it appears to be intersecting, see the black ring where the glass 'rests' on the ground. Maxwell renders that properly.

Also, it would be very nice to have attenuation for dielectrics in Octane. (I forgot to re-render in Maxwell with no attenuation -- d'oh!) I assume it's on the drawing board, but I still miss it. How much do I want Octane-speed dispersion and complex IOR? VERY, VERY MUCH, thank you.

(I don't have a sig set up with my computer specs yet, but here they are for reference: Phenom X4 9550 @ 2.20Ghz, 8 gigs of ram, Win7 64bit, GeForce GTX 260 @ 576MHz, 216 core)

[Sam]

Do you used Pathtracing ?
The black area are where the rays doesn't go
That's maybe because you are using directlighting
or that you don't have enough bounces

For modelling, I don't have any experience in glass / liquids

[Voidmonster]

It's pathtracing, but you might well be right about the bounces. I'll run it again before I head to bed with 32 or 64.

Just to be sure.

[understand]

i only know the MODO technique which i haven't yet rendered in octane.

You got a contained glass mesh and a closed mesh of the liquid.

The liquid mesh is a little bigger than the space inside the container (1% or so) and it overlaps the glass mesh.

render

[[gk]]

http://splutterfish.com/forums/showthread.php?t=23804

that how you would do it with a render engiene like brazil2

[SurfingAlien]

Hi!
first, no expert here!
I'm wondering... when using physically based renderers shouldn't we use physically based modeling techniques (i.e. give each surface the correct relative IoR and avoid overlapping/space between glass and liquid)?
this is definitely a question and not an answer... I'm interested because I'm working on a similar scene too

cheers,
Alessandro

[radiant]

The second one looks to obvious [water in class].
But they look both have class and style

[understand]

oh great..just found out that Sun Light isnt penetrating glass in octane just yet.... so i guess make sure you are using hdrs

[Voidmonster]

I re-rendered with 256 bounces. Of course, the original render had 32 bounces, so I guess I shouldn't be surprised that cranking it way up didn't change anything. It even rendered at about the same speed -- 32 minutes to reach 16,000 samples.

I'll try a couple of other methods for modeling liquid-in-glass, but I'm very curious about that black ring at the base. It really looks to me like an intersection. I wouldn't be terribly surprised if the unit conversion is whacking me, but nothing else behaves as though the scale is off. Years of using Maxwell has taught me to make everything the correct size.

[radiance]

there's a tutorial by philbo somewhere (can't remember) on the forum.
maybe use the search function, it includes a diagram of how to make the liquids/meshes.

Radiance