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Old 03-01-2013, 09:49 PM   #1
Broodstar
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Michael Rauwerdink
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Vray Light Fog

Hi hi

I have searched the internet high and low, including this forum, but I cannot find any useful information on how to create light rays in vray. From what I have gathered people keep mentioning the vrayenvironmentfog but I have no idea where to plug it in.

Also there is a vray scatter fog node, which I assume is exactly what I need, but again, where do I plug it in? Do I use it on geometry, in a light or in the render settings?

Help!
 
Old 03-02-2013, 01:18 AM   #2
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Render settings.

Check "Use environment volume", and drag n drop the vray envfog shader onto the "Environment shader" slot. after that just tweak the shader settings to get the effect you want.
 
Old 03-02-2013, 04:45 PM   #3
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thanks for the reply. I did that but it just renders black. What kind of light must I use? Any other setting I must change?
 
Old 03-03-2013, 06:25 PM   #4
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Richard Culver
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Lets see, if memory serves me correctly it is because it is a fake. I think it is the same as in Softimage.

My email to support:

Quote:
When you add volumetric effect it blocks out the Environment light

source entirely. So if you have a scene set up with VRay Sun Sky set up

you completely loose the visibility of the environment. Does not matter

the settings for the volumetric light. You can make it transparent and

the background renders black. Remove it and the sky returns.



Then the volumetric light settings are impossible. There are no sett

ings I found that actually make god rays visible clearly and also have

it so that the light is not so bright it washes out the objects.



So what you get is 1) Volumetric with settings that either don't make

sense (my user error) or don't work. 2) Volumetrics making lighting a

scene with the environment impossible. (Based on my knowledge)



I need GI with brute force illuminated by environment and working

Volumetric lights together. No post process.



If you can have a technician address these issues that would be great.

Kind of tired of playing around on the forums when I need serious

answers to these issues.


The response:

Quote:
Dear Richard Culver,

According to your question about VrayEnvironmentFog and Volumetric Lights we want to inform you:

About VrayEnvironmentFog:
Currently there is a limitation with the VrayEnviromentFog and when it is turned on the background become black. This is a known issue and our developers are working on it and it will be fixed very soon! However there is a workaround in this situation - it is possible to set-up your scene with a large sphere or plane and use this objects as a background. This way the fog is working correctly and the background is visible!

About Volumetric Lights:
Once the VrayEnvironmentFog is set right adding volumetric lights is easy process. Just add some directional lights and VrayEnviromentFog will make them volumetric. The rays are visible and the objects are not washed out!

We are sending you a scene file created with SoftImage 2012 SP1 and Vray 1.5.
Global Illumination is set to Brute Force/Brute Force , VrayEnvironmentFog is added to Passes Shaders > Volume , VraySun is main light source and SpotLights with small angle are added for God Rays, a simple plane is added for background!

The result is exactly what you want - Volumetric God Rays rendered by BruteForce/BruteForce!

Please let us know if this information helps you with this issue!
If you have any questions about the scene set-up , or anything else about Vray or our other products don't hesitate to ask us!

Regards
Svetlozar Draganov


My rebuttle:

Quote:
Hi,



I finally got a chance to check out your scene file using the demo limited version.



I can see from your example that I was not clearly understood as to the problem with Vray. In the attached scene you can see that there is almost no contrast at all in the volume lights from the fog background. Yet at the same time where they hit the object it is completely washed out. In a typical scene of this nature, the fog would be almost undetectable and the volume light would have sharp contrast to surrounding pixels. This is impossible to achieve currently with Vray from my experience. And if this is your best attempt that is confirmed. And actually it is more typically the case that fog is not required to

create volume shadows and this is the main drawback and limitation of

Vray and other 3rd party render solutions I have run into. I am not sure why this it is so difficult to simply use the Volume light effect with Softimage or write a shader or light to produce volume lights without the use of fog. This would be more in keeping with the typical workflow that has been proven over time to produce fast, predictable, useable results. Voume light with fog should be an option, but it should work in this scenario. Currently it does not. It would be better in my opinion to simply code a light that can produce volume and use objects in front of them to create shadows. (God rays through clouds, light streaming in through a window) The volume effect can be worked on. But I think it is problematic by nature, as most of the time in the real world fog is not required to produce this effect. It is rather dust particles or gasses etc in the atmosphere that get illuminated and are usually otherwise not visible.



Secondly, it is not where the light hits the object at the end of the ray I was talking about. Though that is clearly an issue. The Balls need to be the source of the volume shadow. Not several lights. So where the light hits the object that creates the colume shadows from the volume lights, they are unnaturally over lit and blown out. This is not natural.



What is needed is a natural looking light source that creates a volume shadow.



The reason fog is not workable for this is because by nature, there would never be contrast if the fog is to be visible in the BG. The result is that the light values get cranked to show anything and this blows out the things they hit. What is needed is Volume Lights without fog.


They never responded on this issue after that. Currently in Softimage it actually does not work in a useable way - from my tests.

Hopefully it does in Maya. I will be interested for sure if you can get it working.

 
Old 03-03-2013, 10:36 PM   #5
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Normally I try to limit fog to geometry. You do this by applying VrayMtl to an object, set opacity to 0 and plug Vray Environment Fog to the shading group's Volume material.

If you only want light rays and not fog in general, you can parent a cone geometry to your light and apply fog to that.

Vray Environment Fog is the only fog I use. I can't really get Scatter/Simple fog to do what I want, but I haven't really played with them for a while already.
 
Old 03-04-2013, 04:59 PM   #6
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Quote:
But I think it is problematic by nature, as most of the time in the real world fog is not required to produce this effect. It is rather dust particles or gasses etc in the atmosphere that get illuminated and are usually otherwise not visible.
In nature, there is no such thing as "otherwise not visible" - gasses and particles still block out a bit of what's behind them. So using fog to represent this effect is a perfectly valid solution. However, the density of the fog in that case is very low, while the intensity of light sources (typically spot lights and the sun) is very large. At the same time, the volumetric rays are usually a very subtle effect (at least in exterior scenes) - which means that the renderer may have a hard time to sample the right places.

I realize of course, that you may want a different effect in the end, which may or may not be physically accurate. In that case rendering the volumetric lighting separately and adding it as a post effect, will probably work better in most cases - plus, you can adjust the intensity as needed.

Best regards,
Vlado
 
Old 03-04-2013, 06:31 PM   #7
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Quote:
Originally Posted by thev
In nature, there is no such thing as "otherwise not visible"


Sure there is. It is called what is "visible to the naked eye". And this is in the field of optics, I suppose if we are to classify it.

The bottom line is that it it does not work so it is not a valid solution to me. Maybe in theory it might seem logical but it falls apart immediately on application. Because I think it has more to do with optics than with the psychics of gasses and particles alone. Just to take a stab at it.

But however you want to spin it. It does not work.

I'd rather have a cheap fake in this case rather than something that attempts to be real (whatever that may actually be) but fails.

The scene they sent me as a solution, did not work! If anything it was a better scene to send them to describe the problem. And they did not have an answer. Because there is no answer. This is fog. It does not work to fake or even produce the real effect of particles illuminated by light in a controlled way.

So the answer is, there is no solution for volume lights and shadows in Vray.

The solution is to render in Mental Ray and fake it with Volume Lights.

Or as you say, do it in post.

Hence my plea. Just write a shader for a light. Done.
 
Old 03-05-2013, 10:26 AM   #8
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I think what Richard and others are missing in the VrayEnvironmentFog is the capability to reproduce the effect of light scattering in tiny liquid particles in the air. This humidity will not block the light, only reflect and refract it in a way that makes it visible to us without creating any darkening effect.
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Old 03-05-2013, 12:37 PM   #9
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Not missing that at all.

But again. This does not make the effect work or useful for volume shadows which was specifically what I asked for in my email to support.

From my tests - and what Chaos group confirmed it is not useful for volume shadows.

If you have other uses for this great.

If the OP can use the dome trick as a solution great just to see the BG and have fog. Happy to help.

I only included the other parts of the email exchange as additional info for my particular situation.

If you want to prove me wrong. Please. Whip up a scene. I'd love to be wrong.
 
Old 03-05-2013, 03:06 PM   #10
lostparanoia
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Quote:
Originally Posted by cineartist
Not missing that at all.

But again. This does not make the effect work or useful for volume shadows which was specifically what I asked for in my email to support.

From my tests - and what Chaos group confirmed it is not useful for volume shadows.

If you have other uses for this great.

If the OP can use the dome trick as a solution great just to see the BG and have fog. Happy to help.

I only included the other parts of the email exchange as additional info for my particular situation.

If you want to prove me wrong. Please. Whip up a scene. I'd love to be wrong.



I wasn't trying to prove you wrong. I was trying to clarify what I thought you were looking for. I meant "missing" as in "the feature is missing from the program".

Now I see that either I don't have a clue what you're talking about, or you don't have a clue what you're talking about. You were talking about an optical effect and the only optical effect present in volumetric light in the real world is that of humidity and particles refracting and reflecting light. Anything else you perceive is glow in your eye or in the lense of the camera. That's something you should add in post and not be doing in you 3D app.
Even more likely is that you expect something to happen that actually would not happen in the real world. I assume you know that shadows are not a thing. Shadows are only absence of light. I just whipped this up and it seems to me that it's working just like it should. http://i1052.photobucket.com/albums...tricShadows.jpg
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Old 03-05-2013, 03:37 PM   #11
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We are tracking 100 percent. I think understand the physics of it pretty well. And what you said, is fine with me.

It is the example I have an issue with. Reference my note to Chaos above.

I don't have the scene in front of me, however it does look like the same issue in Softimage. But Maybe not. Maybe Maya is a better implementation and that would be good.

I explained it fairly clearly above.
 
Old 03-05-2013, 05:23 PM   #12
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Ok, I did another test and I think I see what you mean. The problem becomes quite apparent in larger scenes.

The way I see it, the problem arises because "Fog density" for some unknown reason is capped at 1. In a large scene you will probably need to have a very high "Fog distance" in order to encapsulate your entire scene. This makes the fog very thin, and you have no way of increasing it's density. I can see why this becomes a problem when making things like god rays.
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Old 03-05-2013, 07:32 PM   #13
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Thanks for testing that. I don't have Vray installed in Maya at the moment.

Pretty much it in a nutshell.

I wish they'd just do their own version of a fake volumetric light.

That would work for me.
 
Old 03-06-2013, 12:41 PM   #14
lostparanoia
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Well. let's hope Chaos group fixes that then. It should be really easy. I see absolutely no reason why it should be capped at 1...
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Old 03-08-2013, 12:49 PM   #15
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Here's to hoping!
 
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