I am dealing with a very large 3d scanned mesh that has a lot of unnecessary detail:
I am looking to create one coherent mesh that is only the outer surface of the city model, without the "inner" and "below surface" vertices. (Imagine it like a layer of fine dust settling on a city)
My first approach was to manually apply a selection from top view, but the process is tedious and selection is too inconsistent. A lot of people on here asked to delete the "interior parts" of meshes. However the proposed methods like Blender's "Select interior faces" are not really applicable to my case.
A member of the SideFx forum called "zarti" provided a clever way to delete inner parts of meshes in Houdini, that uses a ray node. I tried to alter this method to work on my model with Blender Geometry Nodes (Raycast Node). It seemed very simple but I was not familiar enough with the logic of the Blender Geometry Node system.
The basic idea is to cast rays onto the models from -z direction and delete every face that does not get hit.
Of course this method would be still too brute and would need some refinement, like some kind of angle deviation or "diffusion" to hit all the relevant faces.
In that respect I also tried methods of baking different maps (Diffuse/Shadow/AO) onto the vertex color map and select/delete vertices accordingly, but the results were very messy.
Maybe someone with more insight into the Blender Geometry Nodes System could help me to find an elegant solution for this problem.