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

nop head nop.head at gmail.com
Sat Nov 16 09:07:03 EST 2019


Yes because STL is only for making real things, so it never needs to be
able to represent that physically impossible shape. I still can't see why
anybody would want to or why it is a problem. Just refuse to export in to
STL in OpenSCAD.

On Sat, 16 Nov 2019 at 13:04, Doug Moen <doug at moens.org> wrote:

> On Fri, Nov 15, 2019, at 9:59 PM, Michael Marx wrote:
>
> On the topic of, can we detect and/or fix it. I started with an edge.
>
>
>
> Netfabb reports two 10x10x10 cubes with a shared edge, as having two
> holes, and also highlights the edge as a self-intersection.
>
> GUI repair doesn't fully fix it, the holes go away (ie the count in the
> repair stats = 0), but there is still a self-intersection, on export it
> shows:
>
>
>
> The Netfabb export dialog says "Some file formats do not include enough
> information. This may result in errors."
>
> Translated, that means "The STL file format does not include topology
> information. This may result in errors.". Most (all?) of the later mesh
> file formats used for 3D printing include topology information. So we might
> expect different results if we use a different file format.
>
> I only have Netfabb Basic, which doesn't do automatic repairs, so I used
> MeshLab instead for my first test.
>
> In OpenSCAD, I exported this model:
>     cube(10); translate([10,10,0]) cube(10);
> to STL.
>
> When import into MeshLab, it detects corruption, and asks if I want to
> repair it. The dialog says "Unify duplicated vertices?".
>
> I say yes, and MeshLab performs the repair. Then I export to an OBJ file,
> which includes topology information. Then, when I import that same OBJ file
> into MeshLab, it does not report any errors.
>
> If use OpenSCAD to export this model as OFF (which includes topology
> information), then I can import the OFF file into MeshLab, and it does not
> report any errors.
>
> When I import the STL file into Netfabb Basic, it reports an error. When I
> import the OBJ file into Netfabb, the mesh is clean, no error. (My version
> of Netfabb doesn't read OFF files.)
>
> Based on these tests, it appears that the problem is with the STL file
> format, not with the model.
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