Normal repair

[czc98]

Hi!
I have a closed triangular mesh, but some faces on the model have reversed normals. Is there a relatively simple method in meshlib to detect the reversed faces?

[Fedr]

Hi,

MeshLib's representation of meshes requires consistent orientation of neighbor faces (both must have normals in same direction). So most probably, you will not be able to load your mesh without some losses in such triangles.

If you can attached some example, we will look at it.

[czc98]

af3cea55-86ea-4348-8566-1b54693ae2a5.zip

[Fedr]

Thanks.

When such file is open in MeshInspector, one will see

So all vertices along the boundary among inconsistently oriented triangles are duplicated, and a boundary appears among such areas:

To fix such mesh, please

1. Manually Flip root component by picking it by mouse:
   

2. Then Unite Close Vertices to stitch the boundaries:
   

Does it work for you?

[zhangjiangzhao123]

So I want to know what the API interface function of MeshLib corresponds to this operation, and I really need it.

[Grantim]

Hello!

1. MeshLib/source/MRMesh/MRMeshTopology.h

   Lines 439 to 443 in 0eb98b4

   	/// flip orientation (normals) of
   	/// * all mesh elements if \param fullComponents is nullptr, or
   	/// * given mesh components in \param fullComponents.
   	/// The behavior is undefined if fullComponents is given but there are connected components with some edges included and not-included there.
   	MRMESH_API void flipOrientation( const UndirectedEdgeBitSet * fullComponents = nullptr );

2. MeshLib/source/MRMesh/MRMeshBuilder.h

   Lines 113 to 119 in 0eb98b4

   	/// the function finds groups of mesh vertices located closer to each other than \param closeDist, and unites such vertices in one;
   	/// then the mesh is rebuilt from the remaining triangles
   	/// \param optionalVertOldToNew is the mapping of vertices: before -> after
   	/// \param uniteOnlyBd if true then only boundary vertices can be united, all internal vertices (even close ones) will remain
   	/// \return the number of vertices united, 0 means no change in the mesh
   	MRMESH_API int uniteCloseVertices( Mesh & mesh, float closeDist, bool uniteOnlyBd = true,
   	VertMap * optionalVertOldToNew = nullptr );