Deleting overlapping shapes (with Geometry Nodes)

Question

I'm using Geometry Nodes to instance shapes in my scene and I'm trying to figure out if those instances overlap with another specific object. For the sake of simplicity, the specific object is a cube . If the instances do overlap, I'd like to delete the entire instance – not just the non-overlapping geometry (generated by the boolean operation).

My approach involves using a Mesh Boolean node and then testing if the point count is non-zero (using a Domain Size node). For this approach to work, I've had to realize instances. Here's what my node tree looks like:

Unfortunately, this doesn't work as expected. I'm guessing since I'm trying to delete the geometry that's generated further back in the chain, still stored as instance data. If I connect the output of the Mesh Boolean object, to Delete Geometry, I get the boolean difference but that leaves some artifacts that I don't want in the scene.

I know that you can use attributes to access data down the chain but is there anyway to send data from a realized mesh back to an instanced mesh?

Thanks for any tips/advice you can share!

Answer 1

If, as shown in your example, you are really only dealing with upright cubic shapes, then the node Raycast may help you.

With it you can check in this case, and without the computationally intensive process with Mesh Boolean, if another object crosses the path somewhere on the Z-axis.

Something like this:

Of course, you still need to use the Realize Instances node, since you need the individual points in this case. From each point you send a raycast up (or down). If there is a hit with another object, then you accumulate this value per mesh island and get a selection to delete the whole object.

_{(Blender 3.6+)}