Vray Light Fog

#4

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:

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:

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:

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.

[img]http://sn141w.snt141.mail.live.com/mail/clear.gif[/img]
#5

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.

#6

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

#7

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.

#8

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.

#9

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.

#10

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/s443/lostparanoia/volumetricShadows.jpg

#11

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.

#12

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.

#13

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.

#14

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… :curious:

#15

Here’s to hoping!

#16

I saw your thread the other night, and you are not alone.

Here are some links that I found on the subject -

Mostly a max/xsi user myself

http://www.peterguthrie.net/blog/2009/03/canova-museum-take-3/

http://www.fourdimensions.co.uk/wordpress/?p=499

http://cgworkshop.org/forum2/showthread.php?50-Vray-Volume-Light-and-Vray-Fog-%29

The links work based on vray although since you are in maya- but I’m sure you will find their equivalent.

Drove myself nuts for a while sometime ago DIY
( without just stopping to look for reference)
but these seem to be the most spot on- but that’s just my take on it.

they may be of some help.

gl.

#17

was just looking for something else in regards to vray and fog and noticed that this post mentioned the fog density is capped at 1.

You can make it go higher than the UI limits if you create an expression, right click it and create VRayEnvironmentFog1.density = 10;
and render, for maya 2014 appears to get denser.

#18

I could be wrong, but couldn’t volumetric fog also simulate dust particles being illuminated, and not just water vapor? In which case, the IoR would be different perhaps, but obviously the visual effects appear similar, often. Depending on the dust medium - gritty, dirty, or sandy dust would be kind of a different story. But not the same optical or physical effects.

One problem from the programming end of this, and why I imagine it’s so difficult for any rendering engine to reproduce accurately, is the gigantic fudge that is Rayleigh scattering. It doesn’t work to explain our own atmosphere and sky, and I would guess that when the coders plugged this in to their rendering engines they realized this and had to go with some other mathematical fudge to get anything to resemble what we see in real life. This is of course true with all atmospheric math, in all the applications and renderers, but likely becomes much more evident when we get to volumetric lighting and sunbeams.

I digress (of course), but I’m about to finally switch over to Vray and it’s key to know what limitations still exist, if any. Volumetrics won’t kill my decision in this case.

#19

The only raytracer that handles volumetrics and fog easily&fast is Arnold. Actually it handles volumetrics easier and faster than any renderer I’ve seen. Glass&caustics renders slow in Arnold, but throw in and combine anything else and it doesn’t slow down.

Anyway. To get those tiny reflecting particles in volumetric lights and beams you either would need to fake them entirely in post, or would need to build a dense particle field in your 3D scene. (Preferably making it only show up in the cone region of a spot light)

#20

-Panupat I will have to try this :slight_smile:

#21

What a juggling act. You can’t take a nicely lit scene and simply add fog to some of the lights - you have to re-set all the light intensities in the entire scene all over again, and by different amounts depending on what type and what brightness they are. Then if you’re disatisfied with the fog density and change it ( or a supe tells you to change it), you have to adjust every single light intensity all over again.

I appreciate the realism, but that’s not flexible enough. It’s like forcing us to use both diffuse and reflection for every light all the time, for the sake of realism.

#22

For the record, mental ray is no better, with or without volumetric lighting. It’s about as predictable as an asshole on your elbow. Why? Because the fundamental light equations are wrong, as I’ve been saying for years. Maxwell was close, but even he couldn’t separate light in his equations.

#23

the light / rendering / precalc part of all of this can be like * juggling a bunch of saws while standing on a net of rope. one adjustment and the whole things fails but it is improving. After spending years grinding towards a perfect beauty right in the viewport without any post- its safe to say post almost always wins. There should however be a way to render these types of physical phenomenon with current available computer strengths. Arnold is great although can get a little hungry at times with my machine resources.

What about precalc GI ? the moment you move your lights its the same story anyway- so in those cases the workflow is very linear. I don’t know of any people go in and merge their IRmap/LCmap passes together manually, they just say screw it and recalculate the thing.

Hope i’m not wrong in saying this.