[OpenSCAD] openScad + STL cannot render

Antonio Bueno atnbueno at gmail.com
Wed Jan 31 15:05:05 EST 2018

You can check and fix the normals of an STL with the --normal-directions
option of *ADMesh*:

2018-01-31 20:57 GMT+01:00 cbernhardt <charlie at carols62.com>:

> I believe the problem might be caused by the normal vectors in the STL
> file.
> To test this I drew a 100 x 100 x 100 cube in AutoCAD and randomly drew
> 3DFACES (three dimensional triangular facets) to cover each side, 12
> triangles total.  I then exported the cube as an STL file, calculating the
> normal vector of each triangle as the cross product of the first two sides
> as drawn.
> When I imported the cube.stl  file into OpenSCAD it previewed (F5) and
> rendered (F6) correctly but when I added an OpenSCAD object (i.e. an
> extruded polygon) both objects previewed correctly but rendering (F6)
> caused
> the STL object to disappear.
> I wrote a routine inside AutoCAD to display the normal vectors when
> importing an STL file and discovered that some of them, depending on the
> direction in which the triangle had been drawn, did not point to the
> outside
> of the cube.  After redrawing the suspect triangles so that all normal
> vectors pointed to the outside of the cube, everything worked correctly in
> OpenSCAD.
> I don't know if there is a program to automatically "fix" the normal
> vectors.  Perhaps some of the more experienced OpenSCAD users know of such
> a
> program??
> Charles
> --
> Sent from: http://forum.openscad.org/
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