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Help with special (needles) scatter rotation case please :)

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Help with special (needles) scatter rotation case please :)

Unread postby atnreg » Tue Feb 25, 2020 3:42 pm

Hi!

I want to scatter needles on conifer trees and it works fine except that the needles are pointing straight out of the branch.
What I need is to get the needles to 'lean' towards the tip of the branch.

I have tried a lot of things and using distance_to_uv is not awful on simple test but not even close on real geometry. The problem is that when I use gradient to map the output of that node, it seems totally random where the result looks best and it also seems to vary on different parts.

Please see the attached simple Clarisse project, alembic and Houdini hip (in case you want to play with it) :)

As you can see, the 'needles' are setting quite nicely except on 'trunk' so there is something wrong and as said, in real geometry (20000+ branches to scatter the needles) it is totally wrong.

In fact, I would prefer some kind of Alembic property (Houdini attribute) that I could calculate in Houdini to drive the rotation but the problem is that I don't understand how distance_to_uv actually works so I cannot try to mimic it :)

Thank you very much for any ideas!

This is the simple version that is not too bad but not perfect
tmp_capture_01669.png
tmp_capture_01669.png (103.7 KiB) Viewed 390 times


Antti
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scatter_rotation_test.zip
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Antti
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Re: Help with special (needles) scatter rotation case please

Unread postby dboude » Tue Feb 25, 2020 4:49 pm

Hi,

You won't achieve what you want to with distance to UV. You should store a quaternion in Houdini which will drive the instance rotation in Clarisse. (Assuming Clarisse will smooth the values between vertices...).

So first, make a branch in Houdini with needles on each point with the wanted rotation. Store this data as a quaternion in the PTC. Export. Use this property in Clarisse to drive the rotation of the needle.

Good luck !

Cheers ;)
Démian
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Re: Help with special (needles) scatter rotation case please

Unread postby atnreg » Tue Feb 25, 2020 5:15 pm

Aargh, I was afraid of that but hoped that there is some trick on Clarisse for this, maybe using some calculated attribute from Houdini :)
The original geometry has the needles but I want to scatter better geometry versions of needles on the branches and that's why I would need some 'procedural' way to do the rotation...

But now I know it is not possible in Clarisse so I will need to do some preparation in Houdini.

Thank you very much again! :)

Antti
Antti
AMD Ryzen Threadripper 2990wx (32c/64t),64GB RAM,NVIDIA GTX 1080ti,Win10
Clarisse 4.0SP5b,Houdini,Blender2.80,Fusion360,Onyx,ZBrush,SubstPnt...
Started: Clarisse 2016/10 (Py 2017/01), Python 2016/11
No business, just fun :)
atnreg
 
Posts: 534
Joined: Mon Sep 19, 2016 4:20 pm
Location: Helsinki, Finland


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