Correct use of Skylight portals

[Reaversword]

I'm doing some test with skylight portals rectlights, but still I have some doubts and I'd like to know the right way to use it.


In first, Rectlight, never should be resized using Maya scale tool, but it should be resized using "U size" and "V size", even when we gonna use it in Skylight portal mode, right?

Skylight portals should be putted after or before the window crystal? (we're talking with the camera in the interior of the scene)

In the case the window have two or more panes, the correct would be add a skylight portal for each pane, or a single big skylight portal?

Its normal that skylight portals ups render times, for example, from 5 minutes wihout it to 30 minutes with it?. Or this is product of an uncorrect configuration?.

Which is the real purpose of Skylight portals?, give more control over the light enters for a window? Reduct the noise of a interior scene?, avoid Vray waste resources trying to render whats its outside of the window? (Specially in the case of Simple Skylight Portal)

What would be the correct configuration of a window crystal?. Disable contribution to GI/Caustics solution?

[vlado]

In first, Rectlight, never should be resized using Maya scale tool, but it should be resized using "U size" and "V size", even when we gonna use it in Skylight portal mode, right?

I don't think it matters anymore, but using the u/v size is the preferred method, yes.

Skylight portals should be putted after or before the window crystal? (we're talking with the camera in the interior of the scene)

Technically, after is more accurate but there isn't much of a difference.

In the case the window have two or more panes, the correct would be add a skylight portal for each pane, or a single big skylight portal?

Unless the panes are separated by a significant portion of opaque stuff, one portal would be more efficient.

Its normal that skylight portals ups render times, for example, from 5 minutes wihout it to 30 minutes with it?. Or this is product of an uncorrect configuration?

Using "simple" portals may help to speed up the render times with only little differences compared to the full portal.

Which is the real purpose of Skylight portals?

Their purpose is to reduce blotchiness and noise when light inside a space comes from a few (relatively small) windows.

What would be the correct configuration of a window crystal?. Disable contribution to GI/Caustics solution?

This is as you wish. I know a lot of people like to exclude the glass from GI, because it improves render times without altering the final result too much (unless the glass is tinted, of course).

Best regards,
Vlado


What would be the correct configuration of a window crystal?. Disable contribution to GI/Caustics solution?[/QUOTE]

[Reaversword]

Thank you for the answers Vlado.

[Reaversword]

Eeerr.. Appears Skylight Portals provoke noise, right?. How can we avoid it?.

Appears, for rect lights in "Skylight portals" mode, the Shadow samples is disabled, and augmenting light samples neither help. Thinking about maybe Skylight portals get samples inherited from the sun (sky not haves any "samples" parameter), I tried to raise sun shadow samples, but still not better results, so, any solution?

[snivlem]

good thread I have been wondering about these questions for a while.

Can you post a screenshot Reaversword? I wonder about the noise and where it is occuring for you.

One thing i noticed with simple portals is that they are usually much brighter than the regular ones but I guess this is understandable. Vlado, do the simple portals lights take any geometry into account? For instance the ground plane?

[vlado]

Eeerr.. Appears Skylight Portals provoke noise, right?. How can we avoid it?

Just increase the subdivs for the portal light.

Appears, for rect lights in "Skylight portals" mode, the Shadow samples is disabled, and augmenting light samples neither help.

This works fine for me. If you have a scene where it doesn't work can you email it to me at vlado@chaosgroup.com ?

Best regards,
Vlado

[Reaversword]

I'm sorry for the late answer, some illness and fever this past days, now better.

The images snivlem requested:




We can see a more uniform illumination in the skylight portals one, and a less white-clamped areas, but clearly more noisy sofa in the zone of not direct solar light.

The problem with the zone of the table illuminated directly with the solar light remains in two cases, but in sofa is just perfect. Raising Sun Shadow Samples give us control over noise in the transition between solar illuminated zone and GI illuminated zone, but thats all. Raising Shadow Samples of the Rect Lights doesn't avoids this odd noise. I tried too raise the Interpolation Samples of the Irradiance Map, Scene is with Subdivs at 50, Interpolation at 40, but not noise reduction. I still played with Light Cache glossy configuration (maybe the noise was based on reflections of the sofa), but not, in a "lambertian" VrayMtl materials occurs the same.

Effectively, in the non-skylight portals, its easy see splotches of light in the sofa (but its truth render is with low GI settings), of odd shiny-splotches in the table.

Appears Skylight portals smooth the light, avoiding splotches and high white clamped areas, but simply introduce some noise in the GI illuminated part scene.


A simpler scene when we can see the same effect. I don't know, maybe (I hope) there is something incorrect in the settings provoking this "noise" error.



Simple Scene:

ForChaos.mb.zip


Edit: I forgot it: Win7x64, Maya 2012 Suscription Advantage Pack, Vray 2.0 nightly, vray_adv_21501_maya2012_x64_17745.

[snivlem]

Maybe Vlado is best to answer this one.

But it looks like more sun shadow samples needed and more reflection glossiness samples in the couch???

Maybe subpixel mapping could help too

[Reaversword]

Sun Shadow Samples only fix the noise in the transition between the zone solar illuminated with the GI illuminated one. So yes, only in the borders of the direct sun.

Respect the reflections of the sofa, its at 24, no reason for this. But I'm gonna try with subpixel mapping. Thanks for the interest, snivlem.

[Reaversword]

Well, any reason/wrong set up in the scene for the skylight portal noise issue?

[snivlem]

After encountering a similar scene with noise problem the last project I went and found this site maybe you have seen it but it cleared a lot of things up for me.

http://interstation3d.com/tutorials/...yfing_dmc.html

Especially actually in that in cases scenes with higer quality settings (even with materials of 400subdivs in reflections) can actually render *faster* than lower quality settings with noise.

[Reaversword]

You can find a solar-skylight portal noise scene in the #7 replica of the post, below two cubes images (ForChaos.zip).

Its really interesting the tutorial you linked. Thanks for sharing it. I'm gonna do some test raising the dmc samples and lowering other ones. But it still doesn't explained why suddenly appears noise with skylight portals, in the cube case, color should remain without variations, nevermind if samples is taken at the edges of the pixel or in the center... or maybe I'm missing something.

[vlado]

But it still doesn't explained why suddenly appears noise with skylight portals

The portal is an area light source, so some noise is expected based on the subdivs for the portal.

Best regards,
Vlado

[Reaversword]

All right, its done. Just was a stupidity.

Noise was appearing in the non-direct sun lightning side of the objects. It has been enough just turning on "store with irradiance map" in every Skylight Portal of the scene. And well, at the same time, I've checked "invisible" for convenience.

Happy now!.