Geometry nodes - lock distributed position in animation

Question

I have the following setup:

• A plane with an ocean modifier.
• A sphere scattered across this plane using geometry-nodes, with its Z coordinate aligned to the surface of the ocean. In other words, the spheres are "riding the waves".
• The "Time" attribute of the ocean is animated.

When playing the animation, I get the following problem:

The spheres are changing their distribution because the plane's mesh is deforming. I want to lock the spheres' XY positions, leaving the Z free to align with the waves.

This is the geometry-nodes setup for the ocean:

Thanks for any help!

Answer 1

I wouldn't say that Geometry Nodes are the "wrong" tool here.

You would just have to set it up a little differently:

• Just create a grid above the ocean, and distribute your points there. This grid should be placed above the highest wave.
• Then use the node Raycast and the Hit Position generated by it for your Z-Offset.

In addition, the node also provides you with the normals, which you can then use for a rotation.

Answer 2

What version of Blender were you using for this as I get different results using 2.93.0 Alpha - I get a small number of particles popping in and out of existence as the surface moves but most of them stick with the surface as the ocean modifier distorts it. Also, I note that the Join Geometry node in your example has two separate input nodes but the 2.93.0 Alpha version has a single "multi-input" input node, showing you're likely on an earlier version.

Since the Geometry Nodes feature is still under development, I'd suggest re-trying with the latest version and seeing if this improves the situation.