View Full Version : Photons going trough geometry

10 October 2005, 06:43 PM

I have a problem that i think has been addressed here already, but i didnt find an answer. I have a simple scene with a point light, with area shadows inside a revolved geometry, and it works just fine. It acts as a lamp. The lamp has a DGS material with photon shader attached, and that works just fine (i think). The problem is when i turn on photon casting (caustics) for my point light all the photons that should be stopped by the geometry are going trough it and hitting the wall you can see on my picture.

Why is that heppening?

10 October 2005, 07:17 PM
This picture better represents my problem. There shouldent be any caustics on the upper side of the lamp, there shouldent be any caustics on the upper side of the wall, and photons should stay inside the object.

10 October 2005, 07:52 PM
I think you shoud flag the objects that you don't want to receive caustings by setting it to: don't recveive caustics. This kind of setup should also speed up your rendering time.

11 November 2005, 01:37 AM
Ok, i didnt explain what i want to get. I want to get those nice light caustics that you can see when light is near some wall or something difuse.

So i cant set the wall to "dont receive caustics" and light has to be with all caustics flags on because the light "to be precise, the object around point light" has to cast and receive caustics. My final goal is to make realistic lights with IES profiles attached to point lights, but thats not possible when caustics are not working as expected.

Has anyone a sollution for this or some kind of workaround?

11 November 2005, 03:52 AM
Maybe the caustic photon max radius is too high. What happens when it is reduced?

Does it disappear if you move the light away from the wall?

Check out the photon distribution with diagnostics.

And just checking, but there's no transparency in the DGS for the lamp shader, right?

11 November 2005, 12:30 PM
1. I have reduced the caustic photon radius, and i still see the problem. I have attached the picture. You can see the photons on places where they shouldent be.

2. No, the photons are still bursting trought the lamp. you can see it on pic 2.

DGS is not transparent.

I have attached a picture without caustics, so you can see that everything is ok.

While writing this post i have tested something out. If i increse the lamp size or in other words, move the light slightly away from the lamp, the problem goes away. I have attached the picture. But i think thats not a sollution as i want my lamps to be smaller then this one. Resizing the point light doesent affect anything.

I have attached another picture with incresed photon intensity and evething is ok as long as the lamp stays bigger, no photon bursting.

11 November 2005, 12:31 PM
Here are other pictures.

11 November 2005, 08:05 PM
if the photons act ok when you scale the lamp up, then scale all the scene up hehe :D

btw it must be smth wrong with the light... did you turned mentalray Area Light on? did you attach the light profile directly on the maya light or did u use the Photometric mentalray light?

11 November 2005, 01:02 AM
Area shadows are on. No IES light profiles attached if i do, there is no change, photons are still going trough geometry.

I tryed something else, i created a simple box placed a point light inside it, turned on caustics, and turned on photons on the point light. Now someone might think that the render will be black because the light is in the box, but i can see the photons and i get some kind of SSS effect. I dont know what i am dooing wrong...

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11 November 2005, 01:02 AM
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