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Effects of wind beyond level 1 & 2?

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  • Effects of wind beyond level 1 & 2?

    So I've got a good tree model going that essentially consists of a Trunk, Boughs, a further three levels of branches, and no leaves (I'm adding these in Maya).
    I need to have this tree blowing in a gentle breeze, but it appears SpeedTree only actively calculates geometric wind deformation up to a certain point into the hierarchy. Right now I am getting no deformation on my upper two levels of branching, they are only inheriting transformation from their parents. This of course looks very stiff and artificial. The highest level of branches (from which the stems+leaves will sprout) are quite long and need to be swaying in the breeze (think Weeping Willow). I have the 'Wind' property enabled on all the branch generators, to no avail. So how can I make this work?
    Looking into the Global Wind Properties, there are Level 1 and Level 2 controls under the 'Branch Motion' panel. I suspect this is the culprit. Is there any reason this is capped at two?

  • #2
    Apologies for pushing this thread, but I could use some clarification on this issue. Am I doing something wrong or is there a hard limit to wind dynamics in SpeedTree? If it's the latter, I need to start looking for ways to make up for it in Maya. Which is an R&D project I'd rather not have to do at this point.

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    • #3
      Sorry for the delay and you're correct, branch motion levels are the culprit. Without getting too far into it it's capped at two for both performance reasons and model fidelity reasons. Our wind isn't skeleton based and too much independent motion can introduce skewing of the geometry.

      That being said, two is usually enough. Here's how to go about it:

      1) Use the settings in the "Global" group to get the general swaying of the tree, including the trunk.
      2) Check "Apply" in the wind group judiciously. Starting from the root, the first generator encountered with "Apply" checked gets level 1 motion. Continuing on the next one gets level 2. This means you can skip levels and make sure that your long, final branches get level 2 and then tune it accordingly.

      The key here is don't waste a wind level on the trunk - global will take care of that 99% of the time. Use the two indepedent motion levels at target spots in the model.

      Hope this helps!

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      • #4
        Thanks for the explanation Michael. Very interesting to hear that you can skip levels. The shots I'm working on right now only exhibit a gentle breeze, which certainly wouldn't require dynamic deformation on the trunk or bows and maybe even the first branch level.

        I wasn't aware that the Global group would be able to control the trunk in this fashion. That's very useful.

        Thanks again for your help Michael! SpeedTree is slowly but surely revealing it's many layers to me.

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        • #5
          Okay, so that works beautifully.
          A further question if I may... Is there a way to control the stiffness/flexibility of a branch? Obviously a branch of an English Oak tree is a lot more rigid than a long thin branch of a Weeping Willow. Is this in part controlled by the amount of bones? Or perhaps the Segments Accuracy?


          ps. How many posts does it take to pass the moderation phase?

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