(Python) How to reorient mesh normal to point outwards

[thomasm404]

Hello,

I have a series of mesh objects that I am trying to union in Python but some of them have inconsistent normals directions like the mesh pictured below. I want to reorient the normals so that they all point outwards, that is, so that they all appear blue. Can someone please explain how I can achieve this?

By the way, I noticed in Meshlib v3.0.6.229 that such disorientations can now be detected and rectified but I cannot work out from the documentation how to do it.

mesh.zip

Many thanks.

[Grantim]

Hello!

This case is kind of complex because inconsistently oriented parts are joined together and sometimes forms self-intersections and overlaps.

You can try code like this

 from meshlib import mrmeshpy as mm

mesh = mm.loadMesh(__file__+"/../18.stl")

# find disoriented faces
disorientedFaces = mm.findDisorientedFaces(mesh)

# extract them into separate mesh and flip
separateDisorientedPart = mm.Mesh()
separateDisorientedPart.addMeshPart(mm.MeshPart(mesh,disorientedFaces))
separateDisorientedPart.topology.flipOrientation()

# delete disoriented faces
mesh.deleteFaces(disorientedFaces)

# join with fliped disorieted faces (they will be joined but not connected)
mesh.addMesh(separateDisorientedPart)

# rebuild mesh with corrected disorientation to connect all together and fix issues
rSettings = mm.RebuildMeshSettings()
rSettings.voxelSize = mm.suggestVoxelSize(mesh,1e8)
mesh = mm.rebuildMesh(mesh,rSettings)

# optionnaly fix small components
mesh.deleteFaces(mesh.topology.getValidFaces() - mm.MeshComponents.getLargeByAreaComponents(mesh,mesh.area()*0.002,None))

mm.saveMesh(mesh,__file__+"/../res_mesh.stl")

[thomasm404]

Thank you for your help.

For others' benefit, an alternative approach that I discovered is to iterate through all the components of the mesh and invert the normals for all the ones with a negative volume.

mesh = mm.loadMesh(__file__+"/../18.stl")
comps = mm.getAllComponents(mesh)
for comp in comps:
    m = mm.Mesh()
    m.addPartByMask(mesh, comp)
    if m.volume() < 0:
        m.topology.flipOrientation()
...