Ambient occlusion + coplanar faces

[rikou]

Hi,
I just try to use ambient occlusion via V-Ray : Indirect Illumination (GI) panel. And after a few test, I saw a problem with coplanar faces.. (I know , coplanar faces are A problem !). I don't model so I can't have any control to that problem.
Usualy, I have a AO pass via a VRaydirt in VRayExtraTex but I never try this "global AO" option before and that why I wanna test it.
Anyway I just want to know if there is a way to avoid this..

[vlado]

In general V-Ray does not like intersecting geometry, but you can work around the issue if you set the "Secondary rays bias" to a small positive value like 0.001

Best regards,
Vlado

[rikou]

Thanks but it seem to be another problem because I always have my "Secondary rays bias" to 0,001.
This is why I thought this was not something to do with "Secondary rays bias".

In fact, this problem is appear only with AO.

[rikou]

No way to avoid this ? Theoretically, secondary rays bias can act with this problem ?

[Deflaminis]

I've had some success with this little script for vray: http://plugins.angstraum.at/vrayao/index.htm

Pretty sweet. Gives you the option of which method to use (Vray Dirt or skylight) and let's you render your ao right then and there without having to muck with settings much. Works with 1.5 and 2.

I did a little test scene with overlapping items and had no trouble at all. Did a slight levels to darken it up a bit, but very little tweaking needed for this gem.

here's the image, notice there no issues with overlapping. Sure it's cheating a little by using a script, but once you know whats involved in doing it yourself it's not really cheating anymore. :P

[vlado]

Thanks but it seem to be another problem because I always have my "Secondary rays bias" to 0,001.
This is why I thought this was not something to do with "Secondary rays bias".

In fact, this problem is appear only with AO.

I tried a simple scene with overlapping faces, but I did not notice any issues. If you can get me that portion of your scene to vlado@chaosgroup.com, it will be useful.

Best regards,
Vlado

[rikou]

Thank you Vlado
I sent you mail.

[rikou]

Hi Vlado,

Just in case of, did you find some time to have a look to this problem ?
Thanks

[rikou]

sorry to disturb you again but I have the same problem today ... any chance to have a look ? or should I absolutely avoid AO Indirect Illumination (GI) panel ?

[3DMK]

sorry to disturb you again but I have the same problem today ... any chance to have a look ? or should I absolutely avoid AO Indirect Illumination (GI) panel ?

If you model things properly with no co-planar faces you don't have this problem.
I know that sounds simplified but Modeling PROPERLY is the most important step in making 3D renders & I would suggest you do that rather than continually deal with problems associated with BAD MODELS [& believe me ...there are a lot of things that can go wrong with bad 3D models.

Hope this helps

[rikou]

yes, I know but as I said before " I don't model so I can't have any control to that problem."
I totally agree with you because I do 3D renders but people who don't have any touch with 3d renders don't think about it
If I have to modify every models I recieve, it will be really painfull you know ... It's why I ask it again...
Anyway, I can live without AO