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  • Precise tracing flickering

    Hello guys,
    I have a rather simple cloud simulation. The animated volume noise is used to emit smoke. Than there is plain force to move it across the scene.
    After the simulation I set the precise tracing and playspeed on 0,1 (with advection origin and velocity channells exported). However, the result always produce some "jump" after ten frames or so. I tried it in several different scenes made from scratch with slightly different setup and I cannot get rid of it.
    You can see the example here (it is rather low resolution for testing purposes, however with higher resolution grid it is even more visible):
    It is essential for our project, the fluid is moving really smooth without any noticeable "jumps" or stops. I saw several demonstrations of precise tracing and it seems that it should be perfectly possible.

    I am using Phoenix FD 3.12 and Maya 2018.

    In general, I need to achieve developing cumulus-like cloud. I was unable to set the parameters on regular timeline as the smoke was always dissipating and not producing the nice "cauliflower" structures. I was able to get to this result only in very short time scales. So if you could point me to another direction how to achieve this effect, I would be very grateful.

    Thanks.

  • #2
    Hey there,
    we're looking into this right now. I'll ping you as soon as I have more info from the dev team.

    Cheers!
    gosho.genchev@chaosgroup.com

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    • #3
      Hello again, woytha ,
      we managed to reproduce this behavior in a simplified scene. It boils down to how many voxels your smoke travels per frame. The slow-down algorithms work by looking up the grid channel content for the current and next frames and interpolating. So in this case the flicker is smoke that appears out of nowhere in front of the leading edge.

      For the flickering to go away, the base(regular speed) simulation should be slower such that the difference in the position of the smoke in the grid between 2 consecutive frames is reduced.

      Since you've mentioned you're having trouble achieving the desired result at longer time scales, may I suggest trying to resimulate when slowing down your base simulation ? This tutorial (it's for 3dsMax but the workflow is the same) has the relevant info:
      https://docs.chaosgroup.com/display/...eletTurbulence

      I've tested with our simple scene - there's no flickering in the smoke even at 0.1 speed.

      Another possibility would be to try and increase the Scene Scale of the simulator to close to real-world values so the scale of your simulation is correct, and go from there. Note that this will dramatically change the way your simulation looks so please check if resimulating is enough for the task.

      Cheers!
      Last edited by Gosho.Genchev; 15-02-2019, 09:57 AM.
      gosho.genchev@chaosgroup.com

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