[Carrara]Glass, Refraction and Flipping Normals

[Aunty Betty]

I'm running some quick glass test at the moment for a future piece.

I have been attempting to bring in a model from lightwave ( a Martini glass) this has a duplicated mesh with an outer surface and an inner surface i.e a glass duplicate mesh with flipped normals.

I was hoping that this would give me an improved refraction render quality by faking refraction "thickness" but I can see no difference even if I hide the flipped poly mesh in the test renders.

Does Carrara correct imported normals - I couldn't find a way to double check the normal directions in the vertex room.

Anyone with any knowledge on these kind of specifics please help a p'or boy.

I'm most probably am going about things the wrong way

[Couerl]

Ho hum.. I don't think Carrara cares and uses smart back faces by default anyway right?

I did some glass tests a while back and I don't think it's a matter of doubling geometry or tweaking shaders so much as it is adding in another channel for glossiness and maybe adding real world lighting system like IES.

This was the best I could manage in about one or two hours and a fifteen minute render:

http://3dsplash.com/Gallery/Glass%20Study.jpg

I think I can get it better, but lighting is a big key here and something more than just highlight and shininess maybe..

[molaram]

In default carrara import it is set to hide backfaces, if you change it to show backfaces you wont have an issue about flipping polygons. And yes you cant get a realistic glass effect without double faces causing the air between faces to refract light.

[Grendel]

In the vertex room click the little arrow icon on the top right of your viewport. This will pull up a display menu and towards the bottom is a show normal option for vertex/face and so on.

Also have you looked at the 3dxtract issues? There were several glass tutes in them from various people, worth a look anyway.

I've never doubled geometry to get a volumetric feel for glass though.

[Aunty Betty]

Apologies to my seemingly dumb question guys - I've never ever used glass in any render before.

Grendel thanks for that tip and indeed I'd been checking out 3D extract for some speed tips etc earlier on.

molaram - thanks for clearing that up.

Couerl - many thanks for your further suggestions.

Well as usual I can see from tests there's that discrepancy between reality and an artistic reality of a material such as how the impressionists may have rendered glass or indeed most painters. I'm trying to find a happy medium as I don't want the complexity of the surfaces to overpower the overall impressionistic effect.

[Grendel]

Here is a simple martini, it would look allot better in a full scene. Most of the glass characteristics get picked up from the environment they are in.

[bwtr]

http://forums.polyloop.net/gallery/s...searchid=16339

I tried to emulate (see on this gallery site). Patrick made the point that it was important to use caustics in rendering.
You will see in my second effort the great improvement it made.

[jbshorty]

Originally Posted by Grendel

...it would look a lot better in a full scene...

I think it would a lot better in my hand...

shorty

[bwtr]

http://forums.polyloop.net/gallery/s...c=4&userid=810
Only the non-caustic render of mine is here. Will try and show the caustic render.
However, please not that no fancy settings are involved anywhere. All the settings are default. The render settingis default with light through transparency.
(No global lighting settings)
The caustics version attached.

[Grendel]

You're right shorty, that's why it is empty

[Aunty Betty]

Thanks Grendel and Brian for your further assistance.
These added tips have made an enormous difference to the quality of renders!!

I noticed that in Patrick's example and reply to yourself Brian that translucency is discussed - is there a specific recommendation for this setting and what does translucency bring to the render quality ?

I notices as well as caustics being turned on fresnel in reflection is also recommended.

Aside from specific render setting recommendations other tips are:

soft box for local reflections

background for reflections

Use a grunge map to mix reflection
values and bump values.

Many thanks.

p.s although it's a Lightwave tutorial I found this great link for setting up a bottle of Jack Daniels http://www.the123d.com/tutorial/ligh...aniels01.shtml

[molaram]

Some samples i made with Carrara

[bwtr]

I find setting "down" a bottle of Jack Daniels a problem!!!!

Two things.
Experiment.
Analyse the information in the example scenes. Huge learning there. Don't be affraid to use those scenes, transplant your objects into them! (Saves a lot of time also!)

[Aunty Betty]

Thanks moloraram and Brian.
My Giddy Aunt caustics is steep on the ol' rendering.

In some place I found that the light creep from the caustics particularly at the base of the object seemed too spectral / glowy - more so than looked natural.

The main thing is that my basic quality has improved to a point where I feel it'll be good enough for jazz. With the piece I have in mind the glass will be a minor detail yet one where a degree of believability is vital. After much comparison of quality verses time etc I think I'm now happy to proceed.

Thanks again all for your most helpful input.

[Couerl]

Aunty, yes, caustics can give a bit of a neon/glowy effect, but at around 3-5% it actually promotes a bit of glossiness and does help.

Have you done some tests yet? Ice, water and glass are tricky ones I think and I've never seen a Carrrara render that looked "wet" or glossy enough to be convincing. I think you can get it pretty close though..

[Aunty Betty]

Thanks Couerl - great tip

I've never seen a Carrrara render that looked "wet" or glossy enough to be convincing

I know what you mean. I found Lightwave gives more convincing "real world results" as with reflections also.