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General => Terragen Discussion => Topic started by: helentr on March 20, 2007, 03:06:07 am

Title: Caustics?
Post by: helentr on March 20, 2007, 03:06:07 am
Fooling around, I came with this image.
The red part of the shadow of the left sphere looks like caustics. Since that is not possible in Terragen AFAIK, I wonder what it is. Transparency, reflection, GI?

Helen
Title: Re: Caustics?
Post by: RealUser on March 20, 2007, 06:51:02 am
I would say this is simple transparency or translucency. No?
Title: Re: Caustics?
Post by: DiscoBall on March 20, 2007, 08:58:28 am
Translucency or Luminosity.

Coupled with high reflectivity, it can produce that :P

Found out when texturing my plane in TG2 today ^ ^
Title: Re: Caustics?
Post by: rcallicotte on March 20, 2007, 10:27:56 am
Sort of like this...sort of.
Title: Re: Caustics?
Post by: MeltingIce on March 20, 2007, 10:40:08 am
It's most likely the global illumination.  The way GI works is that it bounces light rays off of objects, and takes that object's properties with it.  So when the sunlight bounces off of that red sphere, it casts a reddish glow on the ground.  Luminosity greatly increases this effect, since luminous surfaces actually emit a little light.
Title: Re: Caustics?
Post by: helentr on March 20, 2007, 12:33:18 pm
It could be the global illumination, but I have never seen it so intense before. Even once when I had set GI to extreme values, I only had weak shadows.
There is no reflective shader or transparency or luminance in the scene. I did not change anything from the defaults, except for the render settings. I find it a little eerie  ;)

Helen
Title: Re: Caustics?
Post by: DiscoBall on March 21, 2007, 04:51:29 am
Check your models :p

Maybe the models had high reflective properties/textures already?
Title: Re: Caustics?
Post by: helentr on March 21, 2007, 05:48:12 pm
DiscoBall,

The model (which is uploaded) has specular/reflectivity of 1, which is not too much (or too little) I think.
But this scene is strange in other ways. It occasionally crashes on opening and, every time it is rendered, the results are different.
In this render the "caustics" has moved to another sphere and the lighting on the objects has changed (and it is the same TGD with no changes)

Helen
Title: Re: Caustics?
Post by: Mohawk20 on March 21, 2007, 06:13:50 pm
I still think it has something to do with the GI...

As we have seen in the past, the GI system has a mind of it's own, allways rendering scenes different. Oshyian warned about GI in animations, giving different lighting in every frame, or even with cropped and stitched images. Or what about the red renders?? Those are still showing up too, abort and render again, nothing is wrong.

Just this afternoon I had a render of a vulcanic scene. I had a dark gray base layer, a bright red voronoi pattern surface layer, and a white ash layer. On one of the 10 cropped renders I made (800x600 had to be rendered in 2 halves....) the red layer suddenly had all these orange spots. Rendered again nothing wrong.

All this points towards GI randomness, in this scene too.
Title: Re: Caustics?
Post by: Will on March 21, 2007, 06:43:05 pm
I also agree with the others, I'm guessing its a GI thing.

Regards,

Will
Title: Re: Caustics?
Post by: Oshyan on March 21, 2007, 11:57:43 pm
Yep, almost certainly GI-related. The GI system is still in need of a lot of fine-tuning. It will get more accurate and probably faster as well with further development. But keep in mind it's still a landscape-focused GI system, intended to work particularly well with atmospherics. It's never going to be a candidate for a good result on the "Sponza Test" (http://hdri.cgtechniques.com/~sponza/show_list.php). But you'll be hard pressed to find a better outdoor GI solution. :)

- Oshyan
Title: Re: Caustics?
Post by: Cyber-Angel on March 22, 2007, 02:04:00 am
Could some one test the TG2 render using the Cornell Box Method as I would like to see the results, and would show up areas that need refinement.

Regards to you.

Cyber-Angel
Title: Re: Caustics?
Post by: Oshyan on March 22, 2007, 02:36:36 am
The Cornell Box is largely irrelevant for the same reason that the Sponza test is - the GI system is focused on looking good (and rendering at reasonable speed) over large landscapes and complex atmospheres. It's not designed to work well in that kind of closed environment. Conversely if you took a general purpose GI solution and threw a TG-equivalent landscape scene at it, it would either choke or produce inferior results. It may be possible to "dual-tune" the GI system in the future to allow for great rendering of enclosed interiors as well as landscapes, but TG's real focus is on landscapes, plain and simple, so that's not going to be a priority.

Not to mention that TG2 doesn't have transparency yet so the Cornell Box would be impossible to properly reproduce. ;)

- Oshyan
Title: Re: Caustics?
Post by: DiscoBall on March 22, 2007, 08:06:39 am
Ah I see...
no wonder the red shading was different in each picture...
Title: Re: Caustics?
Post by: helentr on March 22, 2007, 02:44:26 pm
So the verdict is GI. Thank you.
I am beginning to visualize Terragen GI better - it is a little different from the POV-Ray one.

Helen
Title: Re: Caustics?
Post by: DiscoBall on March 23, 2007, 06:53:46 am
Terragen GI seems to be unique, on its own..:P