MeshBooleanUnion improvements?

Most of these are downloads of 3D building data from various public sources - they may be automatically generated by some program somewhere, but there’s zero hope of getting better data for the moment. This stuff is very typical of what an architectural modelmaker has to deal with when doing site models; often this stuff is massive, many hundreds of buildings and they most likely need to be clean, closed meshes in order to be 3D printed…

Right now you need NetFabb or Magics to fix this stuff, but I’d like to show my students that they could do some simple mesh fixing in Rhino. :confounded: