openScad + STL cannot render
Hello,
I dit often now try to put an STL file upon the object created with openScad.
Each time when I do render this the STL objekt is simply gone.
Even as I created elefants with openScad and did put on the speaker box I ceated I could not render it.
On the other hand the STL objekt it self I can render. So no problem inside.
Senciely
Helmut Deichmann
I would check the stl mesh with netfabb or something similar just in case.
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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
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I don't know about the likes of AutoCAD as I'm too tight to buy
propriety software and comfortable with my tin foil hat.....
however in blender you can "recalculate outside", "recalculate inside"
and also flip normals
You can also display normals which I usually do, just as a quick check...
On 31/01/18 19:57, cbernhardt wrote:
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
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You can check and fix the normals of an STL with the --normal-directions
option of ADMesh:
https://admesh.readthedocs.io/en/latest/cli.html#options
2018-01-31 20:57 GMT+01:00 cbernhardt charlie@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
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Saludos,
Antonio
OpenSCAD like most other programms doesn't make use of the normals at all. It
recalcs them from the vertices. You can check that by rendering and
exporting
cube(10);
e.g. to my.stl. Open the STL with an editor and modify the normals as you
like. Then import the result and check:
import("my.stl");
cube(1);
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