Sharp lines in volumetrics ("godrays")

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josephmcs
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Joined: Mon Feb 01, 2021 7:02 am

Sharp lines in volumetrics ("godrays")

Post by josephmcs »

Hello all,

I'm trying to make an interior scene with prominent volumetrics and am having a hard time.

I'm using a cube surrounding the scene with a scatter interior volume to create them.

I've been trying all sorts of setups (spots, sun lamps, area lamps...) and haven't gotten any visible volumetrics at all. The only thing I end up with is what seems like a "foggier" scene but with no dimension to it or interaction with the light.

There are precious few resources online that go deep into volumetrics settings. Can anybody give me some pointers? Attached is a screenshot and the blend file.
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tristan.blend
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tristan test 2.png
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B.Y.O.B.
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Re: Sharp lines in volumetrics ("godrays")

Post by B.Y.O.B. »

You have probably not specified the camera exterior volume.
Set it in the camera properties (near the bottom) to tell LuxCore in which volume the rays from the camera should start.
josephmcs
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Joined: Mon Feb 01, 2021 7:02 am

Re: Sharp lines in volumetrics ("godrays")

Post by josephmcs »

I've tried that with no luck, unfortunately.

Attached is a screenshot of the project's current state. Not ideal as you can see. It's really strange -- I've successfully added a good volume with godrays to the "HallBench" example scene using the same settings but I cannot reproduce it.

Some relevant volume settings that might be useful to know:
scattering scale - .02
priority - 10
absorption depth - 1m
ior - 1.5

What about setting exterior and interior volumes for the different materials on the walls and the stairs? I've seen that done in some example files but it always seems to increase the scattering to a huge amount and whites out the scene when I try it.
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tristan example ii.png
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B.Y.O.B.
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Re: Sharp lines in volumetrics ("godrays")

Post by B.Y.O.B. »

In the scene you uploaded the scattering cube is disabled for final rendering.
After making it visible, it works:
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Capture.PNG
josephmcs
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Re: Sharp lines in volumetrics ("godrays")

Post by josephmcs »

Thank you. Obviously a stupid oversight on my part! I see now that the angle was an issue too and washing the godrays out. You can see them much better when I moved the camera.

But I also figured out what was causing the most problems: I didn't have a fully enclosed scene around my camera. So whenever I tried it with a sun lamp, the scattering from the outside atmosphere was drowning everything else out. I attached versions with a spot lamp and with a sun lamp in case that may be useful to anybody who stumbles across this thread in the future.

One final question if you don't mind indulging me: is there a point to setting the interior and exterior volumes of the other materials in the scenes to the scatter volume? I noticed that it's done that way in the "UnderwaterPainting" example scene but I can't wrap my head around the logic.
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tristan iii.png
tristan iv.png
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Re: Sharp lines in volumetrics ("godrays")

Post by B.Y.O.B. »

In the underwater example scene, it's done more for completeness' sake, because it is intended as an example.

In general you only have to take care of the starting points of the rays (camera, and maybe light sources if using light tracing/bidir/PhotonGI) and any point where the ray should change volume, e.g. when travelling from air into fog or into water. All other surfaces, where a ray just bounces "from fog back into fog" don't need explicit exterior/interior volumes set.
josephmcs
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Re: Sharp lines in volumetrics ("godrays")

Post by josephmcs »

Hugely helpful, thank you so much!
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