Caustics position

[GabrielChahoud]

Hi guys,

Lately I've been doing more tests with caustics on V-Ray for SketchUp, and I was able to understand (or at least I think I did rsrsr') almost everything about it, but there is still one thing that I don't get it and I think it's important. Could you help me, please?

The "problem" happens when I use V-Ray Sun to generate caustics. Look at the image below. The superior right corner of the pool is ~0,75m from the point "0,0,0". In that position and using these shadow settings > Hour 13:57; Data 07/07 everything is working fine.



But if I change the time to 15:40 it doesn't matter how high I set the "Emit Radius" caustics on the Sun Light, Those caustics generated by the sun won't cover the entire pool area (as shown in the image below; emit radius: 1000 ) unless I literally move the model position until I find the area where caustics are. I know it is possible to make it work by moving the model by I don't think it is a very good way to do it, because of two things:

- It isn't accurate, there is no way (or maybe there is and I just don't know it) to know exactly where the caustics will be, we need to try and fail until we find it.
- If I work on a job with complex models and lots of geometry, it wouldn't be interesting having to move the entire model every time I wanted to explore a new lighting by changing sun's position.



Could you help me?

[nikoleta.garkova]

Hi there,

Our developers are aware of the issue you're experiencing and we believe it could be fixed in the next update. Apologies for any inconvenience!

The good news is there is a possible workaround providing a decent result.

You can 'fake' the caustics effect by using a bitmap texture:

1. Set a Blend Material and add your pool tiles as Base Material.
2. Create an Emissive material, and add that material as a Coat on the Blend Material.
3. In the Blend texture slot, add a black-and-white texture representing the caustics.

Apply that material to the pool base and inner walls, and you should have caustics material. Please keep in mind that if there are places where you don't want to see the caustics, you will have to split the geometry and add another desired material - e.g. in places where you have shadows and the caustics shouldn't be visible.

I've prepared and attached an example scene: Caustics test.zip

[GabrielChahoud]

Hi nikoleta.garkova ,

thank you very much for your response and attention. Actually, I managed to use "Photon Mapped Caustics", the one inconvenience was that about needing to move the model sometimes, which I'm glad to know will be fixed in the next updates.
Beyond that caustics is working pretty well

[konstantin_chaos]

Hi GabrielChahoud,

The actual problem here is the position at which we auto-generate the sun light.
It is in fact sort of matching the position of its target.
This doesn't cause any issues at first glance but apparently causes photon emission problems.
The solution from our side would be to move the sun back along its orientation vector, making sure it's outside of the scene's bounding box.

Thank you for bringing this to our attention.

Regards,
Konstantin

[konstantin_chaos]

This problem has been addressed in the latest release:
https://forums.chaosgroup.com/forum/...-now-available

The sun photon emission cone will no longer be cut in halve.
You also have the ability to move the sun cone by changing the origin point of the project.
This way even if the pool is to the side, you'll be able to emit photons exactly on top.

Note that once you move the origin, you'll have to manually change the shadows angle slightly to provoke an update.
Otherwise V-Ray will still use the photon emission cone position.
Another way to force an update is by saving and opening the project.

[GabrielChahoud]

@konstantin_chaos

Sorry if my way to say sounds too informal, but you guys rock! As someone who also needs to deal with the challenge that is running a business,
I need to say, I'm amazed about the way that Chaos keeps an open line to talk with the community and also the efficiency in developing your product!

I'm a fan!
Best regards,
Gabriel Chahoud