Advice Needed - Smooth surface appears faceted when rendering behind clear plastic.

[Brute Guy]

Hi All,

 

Been having this issue for a while and never really got to the bottom of it or how to stop it. Using Vray with 3ds Max.

 

Using irradiance map and light cache.

 

Basically I've got a sealed plastic surface which behind is a smooth flowing curved surface (this is the purple plastic in the image).

 

When I hit render, the surface beneath the clear plastic outer layer appears all faceted, does anyone know why this is happening and how I can prevent it? I've tried a lot of things so far and no luck.

 

In the cross section diagram attached, A is the clear plastic sealed poly-surface and B is the glossy plastic surface behind it. B is very smooth and flowing.

 

Any help would be appreciated.

 

B

 

[Francisco Penaloza]

That could be penetrating geometry, you may want to apply a smooth modifier to the back geometry too, so the fold looks more natural,

Also depending on the number of transparent objects that you have over each other, thy increasing the raytracing depth.

In some cases also Irradiance Gi won't be a good choice for a situation like this. overlapping transparencies is a complex raytracing solution, you could try brute force in both bounces and see how that helps.

[Brute Guy]

Hi Francisco,

 

Thanks for your reply. By penetrating geometry do you mean the two surface are overlapping? In my model I've made sure that there is space between these surfaces.

 

I'll take a look into the raytracing depth, is this the value in the material slot and global switches (see picture)? I have often played with this when overlaying multiple transparencies.

 

As for the Irradiance GI, we did change the secondary bounces from Light Cache to Photon map which did help sort it.

 

Thanks,

 

Marc

[Brute Guy]

[Francisco Penaloza]

the Ray depth , could be changed on the shader but if it is limited (smaller) in the render windows then it won't work, you can set the same number in both.

Regarding Photon mapping, maybe is working better because Photon mapping is less precise. so is creating a large interpolation, if you see the difference with Photon mapping I would recommend then using Brute force.

The latest VRay is more optimized so using Brute force is not that limiting regarding speed, actually, I use all the time, I don't use irradiance any more, you save so much time because of the no need to check settings and testing what it works.

in your case, Brute force in first bounce and maybe in the second bounce too. may ensure you that the GI is a good as it gets, then any problem has to be shader or mesh-related.

 

The geometry overlapping can be self penetration or with other geometry. Check smooth groups or apply the smooth modifier to avoid sharp triangulation.