Help with Volumetric Fog

I must be missing something but I’m d-----d if I can get the Volumetric Fog to show up!

I’ve got “Path Tracer” switched on, plenty of trees / shadows to show it up etc, artificial lights on etc. Attached is the options settings file and the resultant, not very hazy, image after 23 hours of rendering and 100 passes…

Am using version 4.0 LH14

Any pointers gratefully received

▶ Reply to This

Replies to This Discussion

Permalink Reply by Render Plus on October 4, 2012 at 10:26am

Volumetric fog is very tricky - everything has to be right.

Let me take a look and get back to you.

My first guess is that the camera has to be outside the fog volume...

▶ Reply

Permalink Reply by Render Plus on October 4, 2012 at 10:28am

Oh – now that’s interesting. The camera definitely was “within” the model.

Let me know if anything else comes to mind. I’ll play a little with a small simple model and see if that makes a difference.

Yes - start with a small model. It will be easier to get it working. You can tell if fog is working after just a couple of passes with the ray trace engine, even though it is still grainy. Especially if the edges of the fog volume are visible while you are testing.

What I did for my best sample, was to create a rectangular "ground" piece, and then using that for the volume boundary, and I was then able to place the camera outside of the fog volume.

The camera can be within the model, as long as it is outside the fog volume. For example, if you are looking from a hallway into a foggy room, you can make the fog volume match the room, and place the camera outside.

▶ Reply

Permalink Reply by Alain Bonnefoy on October 4, 2012 at 11:45am

AFAIR, there was a very beautifull Drive In rendering few months ago in the gallery no?

Maybe just after you introduced volumetric fog.

Alain

▶ Reply

Permalink Reply by Render Plus on October 4, 2012 at 12:10pm

Yes - that i the one above. (From a model by Museum Maker)

I think I'll go add it to the front page.

▶ Reply

Permalink Reply by Leigh Brooks on October 6, 2012 at 3:52am

Well, I've been messing around with a simple model (couple of trees, rectangular boxes, two lights and 'Susan'). The fog is showing up outside the model clearly (you can see it as a defined box) but I'm not seeing any discernable effect within the confines of the model itself! I'm really trying to replicate the "sunshine streaks through trees on a hazy morning" that is on one of the examples on the Volumetric Fog tutorial. Does anyone know what the settings were for that?? Thanks

▶ Reply

Permalink Reply by Render Plus on October 6, 2012 at 7:48am

Send me the model. support@renderplus.com

Did you set the volume area for the fog to be the model boundary?

▶ Reply

Permalink Reply by Leigh Brooks on October 8, 2012 at 6:22am

Hi, have set a new render running and I've got something that may work now (I'll post it when it finishes but expect it it to take a couple of days to render in sufficient detail to be worth looking at).

The key seems to have been the scatterting setting (I went up to 80%, bit too foggy, but then back down to 60% with abosbtion set at 0% and scatter at 0.2 - found the tip about what these different things mean!).

Without wishing to make work for anyone; how about a page showing the same image with different settings to really get a grip on what the setting change?

▶ Reply

Permalink Reply by Render Plus on October 8, 2012 at 6:35am

I have been working on a sun-streak example this weekend with no success.

It helped to read a few of the tips I posted when I made a sub-streak model a year or two ago. I need to try to see if I can find that model.

If you get one to work, send it along, and I will post some sample images with various values.

If you have a model I can share with others that would be great.

▶ Reply

Permalink Reply by Leigh Brooks on October 10, 2012 at 9:15am

24 hours of renders, over 70 passes, and this was the result. No streaks :-(

Oh, and have no idea what the strangley materialising rectangle box is in the driveway just to the right side of the house... There's nothing in the geometry in front or behind that this relates to! I may simply have to look at post-rendering sunstreaks in with photoshop. At least I'll be able to avoid using the path-tracer render engine which takes an age!

Ah well. Let me know if you have any luck with the settings (I've tried all sorts to no avail including sun behind model, sun behind viewer with negative scatterings etc).