Windows 10 ships with "3D Builder", a Universal App that contains utility functions to prepare STL, OBJ, 3DS, and other files that represent geometries for 3D printing.

The utility looks like this:

In particular, they have triangle mesh functions there that:

• "Detect" when a mesh is not suitable for 3D printing;
• "Repair" so that the mesh isn't right it prepares it, by removing internal faces, closing "holes" in the outer surface, etc.;
• "Simplify" by removing redundant triangles, such as those found to be adjacent and co-planar; and
• "Plane Cut", slicing a mesh through an arbitrarily positioned plane and filling in a surface on that plane to re-enclose the geometry, sometimes followed by a "Detect" and "Repair".

Every copy of Windows 8.1 and 10 has this utility at no additional cost. That says to me that the functions are well-known and as far as I've been able to test, reliable for virtually all inputs to the 3D printing use case. I used some of the messiest STL files I could find to prove this thing.

Which algorithms did they use for those functions? Where are they found for a .NET/WPF/UWP environment?

More to the point, did they expose the functions in an API I can use for a slightly dissimilar use case?

In the builder the functions look like this:

Simplify (the tractor top and sides have fewer facets):

Slice, UI before processing:

Slice, after processing and then one "Simplify" pass:

Windows 10 ships with "3D Builder", a Universal App that contains utility functions to prepare STL, OBJ, 3DS, and other files that represent geometries for 3D printing.

The utility looks like this:

In particular, they have triangle mesh functions there that:

• "Detect" when a mesh is not suitable for 3D printing;
• "Repair" so that the mesh isn't right it prepares it, by removing internal faces, closing "holes" in the outer surface, etc.;
• "Simplify" by removing redundant triangles, such as those found to be adjacent and co-planar; and
• "Plane Cut", slicing a mesh through an arbitrarily positioned plane and filling in a surface on that plane to re-enclose the geometry, sometimes followed by a "Detect" and "Repair".

Every copy of Windows 8.1 and 10 has this utility at no additional cost. That says to me that the functions are well-known and as far as I've been able to test, reliable for virtually all inputs to the 3D printing use case. I used some of the messiest STL files I could find to prove this thing.

The question is: Which algorithms can be used for those functions?

(Secondarily: Where are they found for a .NET/WPF/UWP environment? Did they expose the functions in an API I can use for a slightly dissimilar use case?)

In the builder the functions look like this:

Simplify (the tractor top and sides have fewer facets):

Slice, UI before processing:

Slice, after processing and then one "Simplify" pass: