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'cubic' patterns, voxels freezing, and/or flat spots
#1
Hi all,

Anyone else noticing the following with 'cubic' turned on?
  • 1 - at the start of the sim, the first several frames before voxels spread show a boxlike pattern (i'd call it a cubic patternSmile) down the midpoint of each box side
  • 2 - likewise, after the sim starts to slow down, a linear x and y cubic pattern can be seen within smoke - as if it's moving through a 3d screen door
  • 3 - when temperature and/or pressure start to fade, some voxel areas seem to all of the sudden become frozen in the grid (see QUICKTIME)
  • 4 - the above noticed effect can also show up as what appear to be flat spots (almost like leaves of a tree) where the frozen voxel areas are hitting invisible shelves (see QUICKTIME), might be the same as #2
Perhaps 1-4 are all part of the same issue.

http://webarea.com/uploaded/aroberts/vox...g_test.mov
After you load the quicktime, scrub back and forth to see issues 3 & 4

Btw, with cubic turned off, none of these show up, though unfortunately the sim lacks the detail cubic offered it.

BRIAN DEMETZ
SR. TECHNICAL DIRECTOR
http://www.digitaldimension.com
818 845 2866
4100 WEST BURBANK BLVD, SUITE 200
BURBANK, CALIFORNIA 91505 USA
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#2
Hello,

Here is just a guess of what might be going on. Cubic can probably 'pull' smoke, temp, etc, further away from center to the border of the effect. However, at the border of the effect, velocities might get damped much before the smoke disappears, so you end up with smoke hanging in the area where there is no velocity.
You can try to add some temperature diffusion, increase smoke dissipation strength in order to solve the problem.

Kresimir
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#3
Kresimir,

Thank you very much. Theoretically that is what seemed logical to me - that if the smoke is becoming frozen in place, then it has drastically lost temperature and/or density and hence no gravity nor bouyancy will affect it. I'm still trying some tricks, however the temperature diffusion is one I haven't tried yet.

Any thoughts one issue #1 where a cubic pattern is seen at the start of a simulation? Or is this just the nature of cubic?

Best,

BRIAN DEMETZ
SR. TECHNICAL DIRECTOR
http://www.digitaldimension.com
818 845 2866
4100 WEST BURBANK BLVD, SUITE 200
BURBANK, CALIFORNIA 91505 USA
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#4
"Any thoughts one issue #1 where a cubic pattern is seen at the start of a simulation? Or is this just the nature of cubic?"

Do you maybe have a shot of it as I can't notice it in your animation ?

Thanks

Kresimir
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#5
here is a still illustrating the problem. this is a very large ffx box with fuel/smoke emitting out quickly with high expansion from a noisy sphere. this is frame 20 of a crop of an HD resolution render:

[Image: explosion_J_019-060a21_003.max_f20.jpg]
BRIAN DEMETZ
Senior Technical Director
Final Light VFX
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#6
Hi Brian,

Can you please point me on this image what to look at ?
Do you mean that smoke on the 'ground level' ?

Thanks

Kresimir
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#7
Hi Kresimir,

If you look at the middle of the volume on the front there is a vertical area from bottom to top that looks like a noise pattern that crunches in on the midpoint - imagine a 4 way divider like a cookie-cutter that the volume is rising up through dividing the volume into 4 parts and is causing a noise pattern to appear. The will show up on each side of the ffx box when cubic is active. I should have documented my past cases better because I wasnt able to reproduce it here very well. It was far more noticable in some other scenes in my archives. Please let me know if that doesn't quite explain it. Thanks again.
BRIAN DEMETZ
Senior Technical Director
Final Light VFX
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#8
ok, i think i've found what is causing the 'freezing' problem. when i have 'cubic' turned on, and animate expansion from a higher value to a lower value, the freezing 'leafy' cubic problem shows up, but not when expansion is static. this does not happen with cubic turned off.

it's tragic i'm having to keep from animating expansion because for doing explosions it is usually required to have expansion higher at the intial moment of a blast and then bring it down later on in the blast to keep it from expanding too much. many vfx filmakers also have this problem when filming practical blasts because sometimes they do not expand quickly enough at first so they speed up the start of the blasts in post.

perhaps this might be listed as a bug?
BRIAN DEMETZ
Senior Technical Director
Final Light VFX
<!-- m --><a class="postlink" href="http://www.finalight.com">http://www.finalight.com</a><!-- m -->
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#9
its not in the list of the bugs .. simplify scene and post it on the beta please.. If this is really whats happening , it will be a good 1 !
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