STL compile warning for simplest rotate_extrude() combo
Using OpenSCAD 2021.01 on Ubuntu 22.10.
I have a very nice workflow in my projects, and part of that workflow involves compiling parts to STL format on the command-line. E.g. a UNIX script that would look like this (much simplified for purposes of this discussion):
#!/bin/sh
openscad -o "extrude.stl"
"extrude.scad"
I then have the file "extrude.scad" which looks like so:
pt00=[5,3];
pt01=[7,6];
pt02=[6,7];
pt03=[9,5];
rotate_extrude(convexity=1,
$fn=23) {
polygon(points=[pt00,pt01,pt02]);
}
rotate_extrude(convexity=1,
$fn=23) {
polygon(points=[pt00,pt03,pt01]);
}
I noticed that when combining rotate_extrude() in such a manner (as above) I consistently get STL compile warnings of this nature:
Geometries in cache: 4
Geometry cache size in bytes: 20432
CGAL Polyhedrons in cache: 1
CGAL cache size in bytes: 283680
Total rendering time: 0:00:00.261
Top level object is a 3D object:
Simple: no
Vertices: 92
Halfedges: 622
Edges: 311
Halffacets: 444
Facets: 222
Volumes: 13
WARNING: Object may not be a valid 2-manifold and may need repair!EXPORT-WARNING: Exported object may not be a valid 2-manifold and may need repair
Just wondering. I strive to get rid of all warnings. I feel better that way. I have more of a guarantee that my STL files will play nice with other apps. For example I can union() the two polygon() objects and pass the union through rotate_extrude(). That will solve the issue. But in the general case I am relying on different objects being joined together, and I would like them to compile to STL w/o warnings. If I define polyhedron() myself, bypassing rotate_extrude() altogether, then the compile warning goes away as well. It seems that rotate_extrude() does not play nice with combinations and compiling to STL. Any thoughts? I can work around these issues but it's much work to keep working around it. I thought there would be a simple solution, but after searching there seems to be no simple solution, if I insist on no compile warnings. Sorry if I missed something obvious.
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a. convexity=1 is wrong for this, but that is just a preview issue not your reported problem. (try 4, but 10 is 'good' in general)
b. You have coincident faces, that is non-manifold.
pt00=[5,3];
pt01=[7,6];
pt02=[6,7];
pt03=[9,5];
intersection() {
union() {
rotate_extrude(convexity=10,
$fn=23) {
polygon(points=[pt00,pt01,pt02]);
}
#rotate_extrude(convexity=10,
$fn=23) {
polygon(points=[pt00,pt03,pt01]);
}
}
cube(20);
}
You can see it by the z-fighting
From: neri-engineering [mailto:neri-engineering@protonmail.com]
Sent: Mon, 7 Nov 2022 11:36
To: OpenSCAD general discussion Mailing-list
Subject: [OpenSCAD] STL compile warning for simplest rotate_extrude() combo
Using OpenSCAD 2021.01 on Ubuntu 22.10.
I have a very nice workflow in my projects, and part of that workflow involves compiling parts to STL format on the command-line. E.g. a UNIX script that would look like this (much simplified for purposes of this discussion):
#!/bin/sh
openscad -o "extrude.stl" \
"extrude.scad"
I then have the file "extrude.scad" which looks like so:
pt00=[5,3];
pt01=[7,6];
pt02=[6,7];
pt03=[9,5];
rotate_extrude(convexity=1,
$fn=23) {
polygon(points=[pt00,pt01,pt02]);
}
rotate_extrude(convexity=1,
$fn=23) {
polygon(points=[pt00,pt03,pt01]);
}
I noticed that when combining rotate_extrude() in such a manner (as above) I consistently get STL compile warnings of this nature:
Geometries in cache: 4
Geometry cache size in bytes: 20432
CGAL Polyhedrons in cache: 1
CGAL cache size in bytes: 283680
Total rendering time: 0:00:00.261
Top level object is a 3D object:
Simple: no
Vertices: 92
Halfedges: 622
Edges: 311
Halffacets: 444
Facets: 222
Volumes: 13
WARNING: Object may not be a valid 2-manifold and may need repair!
EXPORT-WARNING: Exported object may not be a valid 2-manifold and may need repair
Just wondering. I strive to get rid of all warnings. I feel better that way. I have more of a guarantee that my STL files will play nice with other apps. For example I can union() the two polygon() objects and pass the union through rotate_extrude(). That will solve the issue. But in the general case I am relying on different objects being joined together, and I would like them to compile to STL w/o warnings. If I define polyhedron() myself, bypassing rotate_extrude() altogether, then the compile warning goes away as well. It seems that rotate_extrude() does not play nice with combinations and compiling to STL. Any thoughts? I can work around these issues but it's much work to keep working around it. I thought there would be a simple solution, but after searching there seems to be no simple solution, if I insist on no compile warnings. Sorry if I missed something obvious.
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I duplicated this with $fn=3, which makes the figure significantly simpler.
I spent a few minutes looking at the resulting STL, and I don't
immediately see anything catastrophically wrong, but I didn't run any
automated analysis on it.
Normally this error means that you have a coincident edge that is not
associated with a coincident face.
One thing that is ... interesting ... is that the resulting figure has
28 faces.
I don't understand how it can have a number of faces that isn't a
multiple of three. The smallest reasonable number is, I think, 12. But
it looks like we triangulate it, which would mean 24. How we get
another four faces is a mystery to me.
Unless somebody else who is more of an STL wizard than I am figures it
out first, I'll see if I can take a further stab at analyzing the
edges. But that's not something I can do "by hand".