Recalculate normals of an object using geometry nodes

Question

Is there a way to recalculate the face orientation (normals) of an object so they all face outwards?

I basically want to select the faces that are flipped (red color) so I can add them to the selection of the flip faces node in geometry node.

So that at the end I can achieve the same result of using bpy.ops.mesh.normals_make_consistent

Answer 1

The following solution works in this case, but may fail with more complex meshes.

First you would have to define somehow where the inside and the outside is.

You can do this by using the node Attribute Statistics to determine the center of the geometry.

By subtracting the position of the individual points of the mesh from this position, you get the direction vector to the respective point.

If then the dot product of this direction vector and the face normal is greater than $0$, then the face is obviously pointing in the wrong direction:

_{(Blender 3.1+)}

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Update:

In your special case, however, you can use this technique, but you would have to apply it at a different place in the node tree.

Since you have two different objects here, which you process with Mesh Boolean, you would have to compare the normals of each of the two objects with those of your additionally created mesh and apply them with Flip Faces.

Something like this: