quad mesh support

[orgicus]

Is your feature request related to a problem? Please describe. Open3D has brilliant support for TriangleMesh. It would be great to be able to use quad meshes as well (e.g. load quad .obj and process adjacency / compute half-edges mesh, etc.) without going back forth between triangle and quad face index juggling

Describe the solution you'd like

• An implementation of a open3d.geometry.QuadMesh class: very similar to TriangleMesh supporting quads
• An implementation of a open3d.geometry.HalfEdgeQuadMesh: very similar to HalfEdgeTriangleMesh supporting quads
• An implementation of a open3d.io.read_quad_mesh function: loads an .obj file and returns a QuadMesh
• An implementation of a open3d.io.write_quad_mesh function: writes a quads .obj file
• An implementation of a open3d.io.quads_to_triangles function: triangulates a quad mesh (input is a QuadMesh, output is a TriangleMesh) when possible (similar to Blender's Triangulate Faces Ctrl+T / Tris to Quads Alt+J option)
• An implementation of a open3d.io.triangles_to_quads function: converts a TriangleMesh to a QuadMesh when possible. (this could be useful with the open3d.integration module)

Describe alternatives you've considered Converting a quad mesh to a triangle mesh in an external editor like Blender, working with Open3D's TriangleMesh class through out (including half-edge), write triangle mesh to file then convert back to quads in Blender.

Additional context Good first ticket ? :)

[syncle]

Thanks for the request. Our team is working on new branches, so the request may not be addressed in the near future. We are always welcome if you are willing to contribute to this feature. :)

[ssheorey]

This is partially implemented in open3d.geometry.TetraMesh. http://www.open3d.org/docs/latest/python_api/open3d.geometry.TetraMesh.html

[orgicus]

Thank you @ssheorey I'll give that a go :)

[TneitaP]

meshio seems to be a library for more diverse mesh type inputs