Understanding mesh_reorient()

[tksuoran]

Hi,
I am trying to understand why mesh_orient() does not seem to do what I hope it would do.
Test:

m.vertices.create_vertices(8);
m.vertices.point(0) = GEO::vec3{0.0, 0.0, 0.0};
m.vertices.point(1) = GEO::vec3{0.0, 0.0, 1.0};
m.vertices.point(2) = GEO::vec3{1.0, 0.0, 1.0};
m.vertices.point(3) = GEO::vec3{1.0, 0.0, 0.0};
m.vertices.point(4) = GEO::vec3{0.0, 1.0, 0.0};
m.vertices.point(5) = GEO::vec3{0.0, 1.0, 1.0};
m.vertices.point(6) = GEO::vec3{1.0, 1.0, 1.0};
m.vertices.point(7) = GEO::vec3{1.0, 1.0, 0.0};
m.facets.create_quad(0, 1, 2, 3); // facet 0 - (3, 2, 1, 0) if flipped
m.facets.create_quad(0, 4, 5, 1); // facet 1 - (1, 5, 3, 0) if flipped
m.facets.create_quad(0, 3, 7, 4); // facet 2 - (4, 7, 3, 0) if flipped
m.facets.create_quad(1, 2, 6, 5);
m.facets.create_quad(2, 3, 7, 6);
m.facets.create_quad(4, 5, 6, 7);
m.facets.connect();
GEO::mesh_reorient(m);

The first three quad facets have the "wrong" orientation. Even if I manually flip two of these, the remaining single incorrectly oriented facet does not get flipped by mesh_reorient(). When I step through mesh_reorient(), it thinks all facets are already consistently oriented.

[BrunoLevy]

Hello,

This is because m.facets.connect() only connects facets along edges with opposite orientations, hence it does not see the connections between the well-oriented and the wrongly-oriented facets (it sees a "border" there that it cannot traverse).
To do what you wanted to do, you can use instead:

	GEO::mesh_repair(m, GEO::MESH_REPAIR_TOPOLOGY, 0.0);

It does in spirit the same thing as what you did, but calls repair_connect_facets() (private function in mesh_repair.cpp) that connects facets along matching edges regardless their orientation, then it calls mesh_reorient() that can do its job.

What are the arguments to mesh_repair() ?

• The first one is a reference to the mesh to be repaired

• The second one is a MeshRepairMode, an | between some constants indicating what should be repaired:
  - MESH_REPAIR_TOPOLOGY: Dissociates non-manifold vertices (always done)
  - MESH_REPAIR_COLOCATE: Merges identical vertices
  - MESH_REPAIR_DUP_F: Removes duplicated facets
  - MESH_REPAIR_TRIANGULATE: Triangulates mesh
  - MESH_REPAIR_RECONSTRUCT: Internal (post-process result of Co3Ne algo)
  - MESH_REPAIR_QUIET: Do not display any message

• The third one is a geometric tolerance to merge vertices