(EmberGen) Voxel size changes are counter intuitive to me

I’ve been experimenting with the voxel size control and its effects on the simulation. Take the default scene for example and scale the voxel size to 5 meters. The container resizes accordingly as you would expect - its now 1000 + meters container. Resize the emitter so you can see some smoke, But the sim itself looks a lot smaller now - everything is moving much faster than before. This to me is a bit counter intuitive as large scale smoke appears to move a lot slower in real life - like a volcano stack. Perhaps I’m mis-understanding the point of voxel size parameter…but there doesn’t appear to be a way currently to have a lo-res simulation in a very large container and the smoke behave in a way consistent with a large scale environment.

Video capture from Embergen

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so for a large sim your voxel size would stay the same and your count larger. if you wanted it to behave simmilar in a large environment. I dont know your level of understanding with fluid dynamics, so I dont want to come off the wrong way. But a way to describe voxels in space. say your in your room at home. that room has square feet cubed that make up the volume of the room. each in this case is a voxel. so your room is maybe 10 by 10 feet just to make the math easy. so your room would have 100 voxels total that fill the room, saying you wanted each voxel to be 1 foot squared. ok with that in mind lets think a room 8 times the size in order to maintain the fluids effect you would have to increase the voxel count, not their independent voxel size. So size 8 times. x= 128 x 8 y=128 x 8 and z = 128 x 8. Back when I used realflow there was this whole thing on pouring a cup of water out. And setting its relative size to a human. So when you were pouring out the water it could spill out like an ocean or a cup of water. this all has to do with voxel size.

Thanks for your explanation it’s really helpful - I’ve previously just used smoke sims casually, so not thought about the math too much before. Given your example, I’ll experiment some more and see if I can make sense of those settings!

One other thing, that is a little confusing to me is the time step. This also plays a big role in how the sim looks. Given my target application is running at 24fps, just wondering how many Embergen frames would be needed for 10 seconds of animation. Do I set the timestep to 24 and loop 240 frames?

Timestep doesn’t quite work like that. Just export 240 frames at any timestep in general if you’re playing back at 24 fps. We’ve noted your concerns about the bounding boxes and voxels but we don’t quite have time to answer it and dive into it right this second (beta launch day!)

Ok thanks Nick - hope the beta launch goes well!