I thought I'd add this observation When adding a mesh in MashLab it offers the pre-checked option "Unify Duplicated Verticies" Without it checked the STL from above has these self intersects <http://forum.openscad.org/file/n16018/ML_non-unify.jpg> With it checked <http://forum.openscad.org/file/n16018/ML_unify.jpg> While it didn't fix everything, perhaps the code used to "unify" could be of use in OpenSCAD? ----- Newly minted Admin - PM me if you need anything, or if I've done something stupid... Unless specifically shown otherwise above, my contribution is in the Public Domain; to the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. Obviously inclusion of works of previous authors is not included in the above. The TPP is no simple “trade agreement.” Fight it! http://www.ourfairdeal.org/ time is running out! -- View this message in context: http://forum.openscad.org/dxf-and-stl-import-rendering-issue-tp15979p16018.html Sent from the OpenSCAD mailing list archive at Nabble.com.

On 02. feb. 2016 01:24, nop head wrote: > The example you gave of the crack is non-manifold if vertices 5 & 7 are > not distinct. The example is manifold and the vertices 5 and 7 are distinct because I told you they are, and it is plain to see. If you think not it is because you are confusing geometry and topology. > STL can represent manifold meshes unambiguously and you > can then do boolean ops on them. Now it is your turn to simply repeat something that has been demonstrated to be incorrect. > As soon as you have topologically distinct vertices that are numerically > the same STL can't represent the topology, I am forced to conclude you are unable to separate between the definition of geometry and topology. > As long as you have the property that topologically distinct vertices > that are numerically distinct then you can convert a mesh to a list of > triangles and then reconstruct the mesh from those triangles. It will be > exactly the same. I am afraid we are wasting time here. As long as you cannot understand that topology is independent of geometry, we get nowhere. You are saying it works only in some cases, although what you call "topologically distinct vertices" isn't what you think, you are thinking of *geometrically* distinct points, and that is not topology. > The weakness of STL is it relies on vertex values not being rounded or > truncated. They must be written and read with great care, especially in > ASCII. You are still talking about geometry. There are no shared vertices in STL, only within each and every triangle. My example yesterday demonstrated that OpenSCAD fails on your criterion "They must be written and read with great care", because when you re-import the result is not the same as the original. Geometry-wise, this is because the coordinates written by OpenSCAD are no better than single precision floats (6 significant digits). > Your multi-step problem is nothing to do with topology. Please do not misrepresent what I said. I said very explicitly "On the question of geometry: I did some simple tests on creating and importing STL file". Now you say it is nothing to do with topology. Right, I told you so. I was demonstrating that the problem with STL is not limited to issues with preserving topology, but it also has issues with preserving geometry. It fails on both accounts. The .scad file demonstrates the geometry problem. > When imported the results are differenced with the non-trucated versions > the result is very thin slivers and OpenScad seems to not be able to > handle them correctly. Right, the geometry is not properly preserved on STL the way it is implemented in OpenSCAD, it is destined to fail for such cases. If you fail to handle both topology and geometry properly and separately, there will be problems. The suggested ways to rectify these problems have already been discussed, so I will not repeat. Carsten Arnholm