Mesh Inverse

I’m using Bison’s shade function to analyse a topography (green), but i need the reverse as well (red). Is there any easy way to do this? I’ve been playing around with closest points and extruding the mesh, but it’s being way too computationally intensive to be practical.

It’s not clear what you are asking.
You might need to post in a specific Bison forum or include your mesh and GH file so someone else who uses the Bison plugin can help.

Is the Green part of your mesh above zero and the red part below zero and you want both parts?

Sorry, to clarify I’m using the shade function in bison on an inputted mesh:


That’s inputting this topography as a mesh:

Which outputs this mesh:

I need a way to get the reverse of the outputted mesh, ie the faces that are in the original mesh and not in the outputted mesh.

Can’t you just do the same but use -Y as the input vector?

Not quite, because it’s looking at how a shadow would be cast on a topography, so it wouldn’t be the same with concave areas for example.

It would be interesting to see how different the result is. I can’t quite visualise it in the concave scenario.

I would create 2 simple, identical meshes and randomly cull faces from one mesh.

Then see if you can create a pattern of mesh face indices that are missing and use this to CullPattern Mesh faces from the original mesh. If you get this process to work then you can apply it on your terrain mesh and shadow mesh (which is likely to take ages!)

I tried this by making a mesh sphere, randomly deleting faces and then trying to find the culled faces without just using the random list. I can get the mesh face centres but can’t figure out how to get the mesh faces… (7.1 KB)

Figured it out using FaceNormals, MeshIndex, and DeleteFaces.

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Great! Did it work on your terrain mesh and how long did it take to process?

Yes it did! And it took a couple seconds to compute, but definitely manageable.

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