How do I scale an instancer by proximity? Not the instance itself

Question

My problem is simple. A box travels on a chain of conveyors. To achieve the effect, we use a curve modifier, and instance the box on a plane traveling down the belt. The trouble is that the instancing plane will cut the top corner. If the instancer were tiny, the problem would happen at the first joint instead of the second. I want the instancing plane to scale down so that it doesn't cut the top corner, by using a proximity node. What's wrong with my node setup? Perhaps it complicates things that my instancer has a curve mod after the geo node mod.

Answer 1

This is an example of a node setup that allows you to scale the instancer without scaling the instances:

That's how scaling the instancer looks with such setup:

Update

My current understand of your problem is that you just want to animate a face following a curve, while also scaling the face to never intersect another, vertical plane. This is a problem that doesn't have a generalized solution in geonodes, because it's known as Collision Detection, and Collision Resolution, simulation-like processes. For example, here's a node tree that animates some triangles and then tries to scale them down as little as possible while guaranteeing they don't intersect another shape:

It has some archaic nodes, but you can open the nodes in newer Blender to convert Transfer Attribute nodes to newer equivalent…

You can see sometimes triangles still intersect, because the check was only done on vertices:

zoom

Instead you could raycast from one vertex to another to check edge intersection, but what if the triangle is impaled through its middle? Then only subdivision can help a little.

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Fortunately in your case the problem seems simple: you can raycast along the curve (and backwards to support scaling on both sides of the obstacle), and scale based on the ray length: