[OpenSCAD] Discuss manifoldness, co-incident faces edges etc

Doug Moen doug at moens.org
Mon Nov 18 13:27:26 EST 2019


On Sat, Nov 16, 2019, at 10:19 PM, Michael Marx wrote:
> In my experience this is not 'detecting' corruption, it asks that for all STLs.

> It does seem to handle bad STLs (I mean really bad like some of the 3D scans), better when you do unify them, but for others it doesn't seem to do much if anything.

> It has not fixed the non-manifold edge, see **Render/Show-non-manif-edges** (and vertices), (**show-non-faux-edges** & **show-vertex-dots** are good too).


Thank you for correcting me on this.

According to my understanding of the 3MF standard, the way that the 2-cubes model is *supposed* to be represented in an OBJ file is by duplicating the shared vertices in the vertex list. This way, if you perform a "2-manifold" check on the faces, then it tests out as manifold.

The OBJ file that I created did not have the shared vertexes duplicated, and as you have pointed out, "Show-non-manif-edges" shows the problem.

I created another OBJ file that represents the 2-cubes model using the correct technique, and meshlab consider it to be manifold. For what it's worth, my slicer considers this file to be valid and slices it without problem. Here it is:

# first cube
vn 0.000000 0.000000 0.785398
v 0.000000 10.000000 10.000000
vn 0.000000 -1.570796 0.000000
v 0.000000 0.000000 10.000000
vn 0.785398 0.000000 0.000000
v 10.000000 0.000000 10.000000
vn 1.570796 0.000000 0.000000
v 10.000000 10.000000 10.000000
vn 0.785398 0.000000 0.000000
v 10.000000 10.000000 0.000000
vn 1.570796 0.000000 0.000000
v 10.000000 0.000000 0.000000
vn -1.570796 0.000000 0.000000
v 0.000000 10.000000 0.000000
vn -0.785398 0.000000 0.000000
v 0.000000 0.000000 0.000000
# second cube
vn 0.000000 0.000000 0.785398
v 10.000000 20.000000 10.000000
vn 0.000000 -1.570796 0.000000
v 10.000000 10.000000 10.000000
vn 0.785398 0.000000 0.000000
v 20.000000 10.000000 10.000000
vn 1.570796 0.000000 0.000000
v 20.000000 20.000000 10.000000
vn 0.785398 0.000000 0.000000
v 20.000000 20.000000 0.000000
vn 1.570796 0.000000 0.000000
v 20.000000 10.000000 0.000000
vn -1.570796 0.000000 0.000000
v 10.000000 20.000000 0.000000
vn -0.785398 0.000000 0.000000
v 10.000000 10.000000 0.000000

# first cube
f 1//1 3//3 4//4
f 3//3 1//1 2//2
f 8//8 5//5 6//6
f 5//5 8//8 7//7
f 8//8 3//3 2//2
f 3//3 8//8 6//6
f 3//3 5//5 4//4
f 5//5 3//3 6//6
f 5//5 1//1 4//4
f 1//1 5//5 7//7
f 8//8 1//1 7//7
f 1//1 8//8 2//2
# second cube
f 9//9 11//11 12//12
f 11//11 9//9 10//10
f 16//16 13//13 14//14
f 13//13 16//16 15//15
f 16//16 11//11 10//10
f 11//11 16//16 14//14
f 11//11 13//13 12//12
f 13//13 11//11 14//14
f 13//13 9//9 12//12
f 9//9 13//13 15//15
f 16//16 9//9 15//15
f 9//9 16//16 10//10

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