Square pattern and stair-steping issue in Simulation

[turner_studios]

Hi,
I'm having an issue where the fire around the emitter has this strange stair step look and then a square pattern look in the first couple of frames in the Simulation. I'm using Vray for rendering but Mental Ray has the same issue too.

At first I use a simple squashed sphere emitter but then I switch it to object emitter and I'm using a texture map in the fuel section of the emitter and I'm having the same issue with both methods.

I'm attaching a couple of pictures of the renders I'm getting, the last one looks ok because it's mostly covered by the smoke but as you can see that's frame 18 so for 17 frames it doesn't look good.

Thanks in advance for any help on this issue.

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[rconover]

Is your time scale extremely slow?
Almost looks like 'voxels-stacked-upon-voxels' with lots of time to 'slowly' shift away from each other.
Also whats your emitter's rate set to?

[sitnisati]

Hello,

Could you please post a scene so we can check it ?

Thank you.

Regards,
Kresimir Tkalcec

[turner_studios]

My time scale is set to 1. I'm attaching the file which was done in Maya 2014. Also is there a way to get more detail in the fire area? The smoke looks great but the fire looks a bit voxelly. I also tried to make a version where it explodes fast and then have the smoke as I have it now but when I animate the time scale, the smoke looses it's billowing quality and it's super dispersed.

Also when I rendered the sequence, the multiple scattering seems to be flickering, not sure what's causing that. It was rendered locally, not on a render farm. Here's the link to the video.

https://www.youtube.com/watch?v=MLFt-4dQ...e=youtu.be

Thanks for your help in advance.

[sitnisati]

Hello,

I have checked the scene and this stepping is normal and unavoidable because FumeFX uses voxels for simulation and your mesh source is slightly sloped.
You could maybe smooth it out a bit if you set the object source type from solid to volume.

As for the flickering. I will sim it and render to see what happens.

Thank you.

Regards,
Kresimir Tkalcec

[rconover]

I have checked the scene and this stepping is normal and unavoidable because FumeFX uses voxels for simulation and your mesh source is slightly sloped.
You could maybe smooth it out a bit if you set the object source type from solid to volume.

Regards,
Kresimir Tkalcec

Another trick that sometimes helps is to have Fume calculate 5-10 or so fames early and key the emitter's rate for the timing that you want. Maybe I'm deceiving myself - but i feel it lets Fume pre-stir the voxels a bit so they birth more oganically. Otherwise you might need to hide the source and have the effect emit through the floor or something. Also for tiney detailed fire I find emitting from a tiney detailed geometry (a geometry with most of the poloygons deleted in a random fashion-leaving only a few scattered polygons) and a tiney detailed noise map (or both) help a lot to scatter flame accross a surface more realistically.

[turner_studios]

Thank you for the 2 ideas. I will try that and report back.

In the meantime, I'm finding out that using Vray Dome lights or any Vray lights that emit soft shadows, create a rendering issue within the smoke. Like cross bands and dark areas. Vray Rectangular lights are fine but I can't seem to use Dome lights unless I set the subdivision to be super high thus making the renders excessively longer.

Although with Vray Rect lights if you set the directional setting to be anything other than 0, it creates the same issue. I'm attaching a picture with the render issue I'm talking about. You can also see at the bottom of each picture, how long each one took to render. One is with One Vray Rect light and a Vray Dome light. The other one is using 2 Vray Rect lights.

[sitnisati]

Hello,

I've reported to Chaosgroup few issues in Vray and still waiting for reply.
They should have been fixed in Vray 3.0, but it seems they are not.
You can try to render without Illumination Map and see how it goes.

Regards,
Kresimir Tkalcec

[turner_studios]

Thank you Kresimir for your response. I'm used Vray 2.45, I haven't tried it with Vray 3.0 Beta but I will do that to see if it happens there too. Also I'm not using GI, that's just when I add a Vray Dome Light or if I have a Vray Rect Light with the Directional setting to anything higher than 0, then it happens.

It sounds like you said that it's a Vray issue but wanted to clarify so if you though it was happening only with GI, you know that there are other things causing it as well.

Thanks,
Mario.

[sitnisati]

Can you please let me know if you've tried to disable the illumination Map with FumeFX and render and the result?
It's usually the problem on the renderer side as they work a bit differently than the Scanline.

Regards,
Kresimir Tkalcec