Rotate Spheres according to height of other points

Question

The flat linear Mesh is displaced and animated and i added Geometry Nodes so that the balls always stay on top of the other mesh. But is it possible to rotate the balls individually according to the deformation of the other mesh?

This is the render but the balls all rotate in the same speed:

Just a question: Don't the points position change all the time when you distribute them on a moving mesh? — quellenform, May 07 '22 at 17:38
No the stay the same but move along the z axis according to mesh — Felix, May 07 '22 at 18:21
OK, I understand. Please share your blend file with us, I am not quite clear about the structure and what exactly should be rotated in which case and how. ...or supplement your question with an explanatory sketch — quellenform, May 07 '22 at 18:32
How do you animate the plane? With geometry nodes or by key frames? This is important to know, because you need the speedvector of the plane to calculate the rotational speed of the balls. — André Zmuda, May 08 '22 at 07:08
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score 3 · Answer 1 · answered May 08 '22 at 06:50

3

I would try this approach:

Use a curve line, raycast this to your displaced plane and then you can move and rotate your balls according to that curve with the help of the sample curve like this:

i didn't fit the rotating speed to the movement exactly...but i think you can fiddle that out (or even solve mathematically)

node setup:

answered May 08 '22 at 06:50

Chris

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Are you sure that's what @Felix meant? Anyway, +1 for this answer! – quellenform May 08 '22 at 08:44
No i am not - but I hope that’s what he meant – Chris May 08 '22 at 08:45
...even if your nodes still look like noodle soup, haha ;-) – quellenform May 08 '22 at 08:47
That’s tasty‼️ – Chris May 08 '22 at 08:50
Thank you for your answer. Yes that is exactly what i meant :) – Felix May 09 '22 at 08:37
you are welcome! if my answer helped you, please click on the checkmark left of my answer. thank you! – Chris May 09 '22 at 08:38

score 3 · Answer 2 · answered May 08 '22 at 12:46

Generating a landscape for testing, where near the Y=0 the plane is flat, and it gets more wobbly further from Y=0:

Wobbly Plane custom group:

You can calculate distance traveled towards each point on the X axis by using Accumulate Field node.

Distance custom group:

You can now create a mesh line for instancing balls, and align it with the plane geometry, so the balls slide not only on the plane, but precisely on the edges of the plane. Since interpolation will be used later, this step might not be necessary...

Align Instancer custom group:

Now use raycasting to drop the balls on the plane and also read the interpolated distance (how much a ball has travelled on the surface).

Drop Down custom group:

What's left is a very simple custom group Object Info:

Perhaps the magic number 157.075 should be calculated there... I got this number by multiplying π by .5 - as that's the radius of the ball, and then by 100 - I honestly don't know where the 100 comes from. I'd appreciate if someone would explain.

I also added a shader to display the distance on the wobbly plane with 10 cm increments:

Thank you for your answer this looks good i will try it this afternoon — Felix, May 09 '22 at 08:35
+1 for the best naming of your blend file :D you made my day — Chris, May 09 '22 at 08:39

Rotate Spheres according to height of other points

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