Mental Ray Volumetric Effects

[CJI]

I have been looking at Peter Guthries blog again and it makes me jealous no end! Anyway, i was looking at his beautiful images of Mies Van Der Rohe Farnsworth House (again!), in particular his environmental effects like subtle fogs and mist. i know his renderer of choice is Vray and his techniques are fantastic. I just started thinking that these things must be possible in Mental Ray, so i gave it a try. On first try i got nothing worth even posting.

 

I will keep trying but i was wondering if anyone else has had similar thoughts or even break throughs on the subject.

 

Mental ray has caught up so much to Vray in arch vis lately and a lot of people say its pretty even however simple things like the ease of the Vray2sided material and the vrayenvironment seem to be frustratingly awkward with mental ray.

 

Im hoping this is just because i've not tested it enough but we will see...

 

Any ideas or comments welcome.

[DanGrover]

One thing I know for sure is that if you're going to do it, use shadow maps on the lights. Just by altering these settings (ie the resolution of the map) you can get a large variety of effects. Using Raytracing is utter suicide.

 

(Note, this is obviously only true is you're actually using shadows - ie, if it's coming in through a window, it actually is, and isn't just a sneaky rectangular light placed in the window - which is always another option.)

 

That said, as an avid MR user who now uses VRay, I still do all my volumetrics in Post. There are some incredible methods to do it that look great still.

[CJI]

I just did a volumetric light effect using a standard direct light aligned with the sun and rendered it out as a seperate pass without GI, FG and Exposure comping in photoshop using screen layer. It worked nicely, used mental ray and got a nice colour bleed through the glass (stained).Shadow samples in this method had to be quite high to avoid shadow artifacts. Render at high rez 3508 x 4981 took far too long, maybe 48+ hours but when i lowered the samples per pixel it came out fine and quick. I am very happy doing things this way but i was just hoping mental ray could match Vray in this example in render?

[Camby1298]

Hey there Uddie,

 

Jeff Patton has pretty much done all the sweat and backache work of figuring out how to work Volume effects of lighting. And luckily he shares it with everyone:

 

http://www.thegnomonworkshop.com/includes/bundles/jpa_bundle.php

 

http://mrmaterials.com/jeffs-blog/107-projected-caustics.html

 

Or another tutorial Done by Ramy:

 

http://3dsmaxrendering.blogspot.com/2009/03/parti-volume-shader.html

[CJI]

Hey Brian,

 

I had seen those Tuts before but i have never had the time to really try it properly and experiment with the settings. Turns out its fairly intutive and once optimised is actually quite fast. This on a simple test, im sure this would be different on a more complex model (anything thats not just a cube with a hole).

 

I will experiment with outdoor mist now, see how that goes. Will post result if i find anything nice.

 

Thanks fopr posting those though, if nothing else they prompted me to pull my finger out, haha.

[Jennifer]

Just FYI, when using Shadow Maps in mental ray, mr always considers the light source to be onmidirectional for purposes of calculating the shadows. Therefore you need high map sizes to get a decent resolution.

 

Jenni