How to avoid smoke growing outside of the grid when using resim?

[LarsSonparsson]

This have happend few times for me.

I have a low resolution smoke sim with adaptive grid (smoke threshold 0.005). Everything looks good until I resimulate it, then the smoke starts to expand over the grid boundaries.
How to avoid it?

[ivaylo.ivanov]

are you using simple smoke transparency?

[LarsSonparsson]

Yes. 0.7 if I remember it right.

[ivaylo.ivanov]

Simple smoke has this "issue", that it doesn't have really fully transparent parts. This means that if the resimulation produces slightly more smoke (which can happen), the transparency will decrease and you will start to see some smoke that wasn't there before. In this mode, the only way is to simulate with even lower threshold or use bigger adaptive margin. But it's too much luck involved. The more robust way is to use manual transparency graph and tweak the first point of the graph a little if you see such issues. This will not change the simulation at all and always works.

[LarsSonparsson]

Ok, thanks. Have to do it that way then.

[Ivaylo Katev]

can you post a image?

[LarsSonparsson]

Here is the original and Resim frame taken from preview png's. It shows the problem well enough.
I think I'm gonna do the transparency curve manually anyway. Not that bit thing. It could be nice to have "extra margin" option for resim only. That could solve these kind of problems.

[Ivaylo Katev]

well, the original smoke also is very close to the borders.
i will ask our coworker svetlin, he is using intensively the adaptive grid (i'm not a big fan at all), as i know he is using the velocity channel as adaptive criteria instead the smoke

[LarsSonparsson]

Yes it is, very close.
Adaptive grid is a real time saver for me. I just have to remember to use enough small threshold.

I also had problem with starting the resim. I have a base simulation 2000 frames. I'd like to resimulate only last 1000 frames, but if I try to do that, I get "grid size doesn't match" or similar error. Is that because of the adaptive grid or is some other limitation?

[Svetlin.Nikolov]

Hmmm, it's a bug. I hope to fix it for tonight's nightlies and I'll keep you posted.

[Svetlin.Nikolov]

Alright, so the issue is fixed in the latest nightly and you can start resimulation of an adaptive grid from a custom start frame There is one more issue though, where again using an adaptive grid, you get the same error when trying to restore a resim, so now I'm working on it as well.

[LarsSonparsson]

Thank you!