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JohnMarston

Gas Upres Node Reducing Detail

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Hey all,

 

I've been trying to take a written out pyro sim and slow it down with a gas upres setup. However, I've run into an issue where the retimed simulation seems to lose detail in the flames when rendered. I've attached both a picture that shows the example in my original simulation and then a .hipnc that has a simple example that shows the same behaviour. Has anyone run into this before? And if so, what did you do to fix it? I have a theory that it involves the shape tab on the upres solver lacking some of the parameters that the pyrosolver contains, but I'm not sure how I'd add those parameters to fix it.

 

Thanks for any help!

post-11749-0-75551300-1409365985_thumb.p

gasUpresTest.hipnc

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That was how I originally tried to slow it down, but it ends up not really working out- it works great for particle systems because each point has a unique ID and x/y/z coordinates that can be used to interpolate their positions somewhere in between the two frames that are actually rendered to fake the in between frame, but because pyro is a volume it doesn't work so cleanly. It introduces a stepping issue where it sort of fades from one frame to the next rather than actually calculating the motion in between. I've just thrown together the same .hipnc but with timeshift this time and set up a mantra node so if you render it out it's pretty clearly visible. Shouldn't take more than a minute or so of rendering to see what I mean. That's why I've been using the gasupres instead- it actually re-sims the in-between frames.

 

gasUpresTest_Timeshift.hipnc

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You can't blend a resizing volume. Copy your pyro sim into a static volume, blend that and it will work fine.

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You can't blend a resizing volume. Copy your pyro sim into a static volume, blend that and it will work fine.

I haven't heard of a static volume before, and I can't seem to find it in the documentation. Would you mind elaborating a bit?

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I haven't heard of a static volume before, and I can't seem to find it in the documentation. Would you mind elaborating a bit?

What I meant by static is a volume that isn't resizing, ie it is always 10x10x10 or whatever size you want. Pyro sims by default have resizing volumes since that is more efficient so simulate, but you can't blend those. So you copy the data from the pyro sim into a fixed sized volume, and blend that. For the size of the volume you probably want it to be the same as your pyro sim when it's at it's biggest.

 

Does that make sense?

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What I meant by static is a volume that isn't resizing, ie it is always 10x10x10 or whatever size you want. Pyro sims by default have resizing volumes since that is more efficient so simulate, but you can't blend those. So you copy the data from the pyro sim into a fixed sized volume, and blend that. For the size of the volume you probably want it to be the same as your pyro sim when it's at it's biggest.

 

Does that make sense?

Yeah it does! Unfortunately, I don't think it's the answer to this problem. I volume resized it to be constant, and then timeshifted, and it still has the fading effect. I threw together a quick video that shows the difference between the gasupres method (left) and the timeshifted, static size volume method (right). You can still see the stepping. It's a convincing substitute when there isn't much change in the size of the volume or the slow-motion effect isn't too extreme, but if either of those are a factor, it becomes apparent what's really happening. (Unless, of course, I'm doing it wrong somehow, haha!)

comparison.mov

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Works fine here, added nodes in red:

attachicon.gifgasUpresTest_Timeshift_dv.hipnc

It still is :( I just upped the buoyancy lift on your file to 200 so it moved fast enough that you could notice it. I'm trying have my fire spread over gasoline from a molotov cocktail, so unfortunately it has to be moving pretty fast, otherwise this technique would probably work.

gasUpresTest_Timeshift_dv.hipnc

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Ah right I see, yes if it's moving too fast or you are slowing it down too much it will look like that - since it's just a straight interpolation. Maybe the Gas Upres is the way to go then, however I haven't used it much so I'm not able to help there. Good luck!

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