Caustics strange behavior with big objects

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PDRA
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Caustics strange behavior with big objects

Post by PDRA » Tue May 12, 2020 11:27 pm

Hi guys,
I'm now dealing with this issue.
I have found that luxcore doesn't create proper caustics effects when I add the landscape geometry in my scene. I've notice that the calculations "disipates" when the geometry gets bigger. I've checked it creating a plane and while I scale it, this issue happens.
I've tried applying a transformation reset to make the scale of it to 1 but it didn't work.
I attach some images of what happens when I turn on and off the geometry.
No terrain and caustic.jpg
Terrain and no caustic.jpg
Is there anyway to tell the engine to not consider this geomtry for these caustics calculations?
Once again any hint will be appreciated.

Fox
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Re: Caustics strange behavior with big objects

Post by Fox » Wed May 13, 2020 12:33 am

I think the border render from small cut out around the subject is one way.
The option for don't store photons on that material, will still spend time on entire scene.

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B.Y.O.B.
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Re: Caustics strange behavior with big objects

Post by B.Y.O.B. » Wed May 13, 2020 1:21 am

Can you post two converged renders with more samples?

PDRA
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Re: Caustics strange behavior with big objects

Post by PDRA » Wed May 13, 2020 2:12 am

Fox wrote:
Wed May 13, 2020 12:33 am
I think the border render from small cut out around the subject is one way.
The option for don't store photons on that material, will still spend time on entire scene.
I am thinking that maybe a way to sort this out is to do the render without the background and later add it with other render... but I don't know.. it would be great to take it in one shot as I'm planning to do many takes from different angles
B.Y.O.B. wrote:
Wed May 13, 2020 1:21 am
Can you post two converged renders with more samples?
I didn't quite understood what you mean with converged, but I added more time to get more samples and I changed the materials to make the effect more evident. Let me know if this is what you meant!
No terrain V2.jpg
Terrain V2.jpg

epilectrolytics
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Re: Caustics strange behavior with big objects

Post by epilectrolytics » Wed May 13, 2020 6:07 am

Maybe this issue again?

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Dade
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Re: Caustics strange behavior with big objects

Post by Dade » Wed May 13, 2020 8:02 am

PDRA wrote:
Tue May 12, 2020 11:27 pm
I have found that luxcore doesn't create proper caustics effects when I add the landscape geometry in my scene. I've notice that the calculations "disipates" when the geometry gets bigger. I've checked it creating a plane and while I scale it, this issue happens.
This is somewhat expected because, as written by Fox, environment light sources emit light from the bounding sphere of the scene (including camera position). The probability to find the caustic paths from a very large sphere become so small to be impractical and often impossible due to (the lack of) numerical precision.
PDRA wrote:
Tue May 12, 2020 11:27 pm
Is there anyway to tell the engine to not consider this geomtry for these caustics calculations?
There are several way to work around this problem, for instance:

1) render the scene with CPU-only, light tracing 100% and a ground plane only large enough to contain the caustics. This type of setup will produce a caustics-only rendering (it is like having a caustic AOV).

2) render the original scene with GPU+CPU, light tracing 0% (but still enabled). This type of rendering will produce a normal rendering without caustics disabled.

3) just add the 2 images and you should get the correct result without having the problem to render the caustics over a very large plane (because they were rendered over a small one).
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PDRA
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Re: Caustics strange behavior with big objects

Post by PDRA » Wed May 13, 2020 4:27 pm

Dade wrote:
Wed May 13, 2020 8:02 am


This is somewhat expected because, as written by Fox, environment light sources emit light from the bounding sphere of the scene (including camera position). The probability to find the caustic paths from a very large sphere become so small to be impractical and often impossible due to (the lack of) numerical precision.

There are several way to work around this problem, for instance:

1) render the scene with CPU-only, light tracing 100% and a ground plane only large enough to contain the caustics. This type of setup will produce a caustics-only rendering (it is like having a caustic AOV).

2) render the original scene with GPU+CPU, light tracing 0% (but still enabled). This type of rendering will produce a normal rendering without caustics disabled.

3) just add the 2 images and you should get the correct result without having the problem to render the caustics over a very large plane (because they were rendered over a small one).
Ok thank you!! I was going to do something like this!

Just in case is there any AOV or method to extract the caustic information only?
I can do the final render mixing the 2 resulting images, but it would be cool if I could extract that info.

This is the same for the depth map.
I've seen the method that Alexey showed on Github in this post to extract AA depth maps but as far as I understood they seem to work just in cycles. Is there any way to achieve the same with lux?

Thank you again all of you guys for the help!

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