5 thoughts on “How to Drift a Car in Blender

  1. Paul Docherty says:

    Hi Jonathan – I posted this the other day but it seems to have disapeared. If not sorry about the double post.

    Having gone through your excellent wheel spin tutorial I am doing wheel spin smoke to apply to footage of an actual car for a film project. Everything looks great except when I go for the hi res renders I get a weird crosshatching artifact hanging in the smoke, especially as it clears. It looks like sets of three lines in alternating vertical and horizontal checkerboard patterns made out of denser smoke, and seems locked in the air with the smoke sort of moving through it.

    I am trying to debug this but it’s difficult as you have to bake the sim before you can render and really see the artifact, which takes hours. I had thought it was to do with the wavelet compression but playing with the wavelet or fft settings seems to soften or harden the artifact a bit but doesn’t get rid of it. I’ve also tried various settings on the bake up to 256 resolution on domain and hi res divisions of 6 but the artifact is still pretty visible as a regular pattern in the smoke. I just wondered if you had any thoughts as to what it could be? I’d post an image of it but I don’t see how to do this on this webpage.
    My deadline is looming fast so any help would gratefully appreciated. Again thanks for the great tutorials!

    Paul

    • jonathanlampel says:

      Hi Paul, I definitely have seen what you are talking about. From testing it out, it seems like the higher the strengths of the wavelet division, the worse it looks. This is kind of frustrating, but I have seen the same results from programs such as Houdini, so it is not unique to Blender. I would not recommend using a value above 2, but even as low as 1.5 can show artifacts. I have also seen the same thing happen with high vorticity settings.

      This really is an issue, so unfortunately the best I can do is offer the workaround of using a lower strength.

      Good luck with the project!
      Cheers,
      Jonathan

      • John Paul Docherty says:

        Many thanks Jonathan. After hours of sim baking and fiddling it has become clear that the worst of the artifacts are created by the vorticity setting, as you suggest. I lowered it bit by bit and eventually got a reasonable result around vort .05 – the default of 2.0 was way too high. With the vorticity down to this level I could run wavelet up to around 1.5 and get a decent look. I’m now experimenting with adding turbulence forces to get some movement back. I’m also trying to reproduce my results in cycles using the 2.71 beta to see if this is more controllable.

        cheers
        Paul

        PS – much as I love this functionality, the “feature” where if you change your path to the baked sim files blender actually erases your entire existing sim cache (which in this case will have taken 15 hours) is pretty annoying. I’ve taken to copying my whole cache just in case, and I’ve used up half a terabyte in storage this way.

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