[OpenSCAD] F5 works, but F6 gives: ERROR: CGAL error in CGAL_Nef_polyhedron3():

Parkinbot rudolf at parkinbot.com
Thu Jan 18 13:03:19 EST 2018


JordanBrown wrote
> On 1/18/2018 1:29 AM, Parkinbot wrote:
>> Indeed I even don't see much sense in restricting STL output to
>> "proper" manifolds. Is it part of the format specification?
> 
> I have no idea whether there's  anything in the format spec, but it's
> quite frustrating to generate something with OpenSCAD, feed it to my
> slicer, and have my slicer misbehave because it doesn't follow the rules.

Currently there is either no hint (emptying the cache can help), or a
cryptic CGAL error or a warning in the case of a singularity. 
The current workaround to have a user defined polyhedron explicitly tested
for manifoldness is to union it with something else (any Boolean operation
will do) starting from an empty cache. 

mypolyhedron(); 
cube();  



> (As best I can tell, usually this happens when there are extremely small
> features that start running into the OpenSCAD resolution limits - like
> when I took my 25.4:1 scale model of my house and then scaled it down by
> a further 25.4:1.)
> 
> (Intuitively, I would say that a string of points that aren't coplanar
> cannot be a face of a polyhedron.  They might be something else, and I
> don't have a problem with having a way to create and manipulate them
> under a different name.)

There was a planarity bug connected with polyhedra faces in the late 2017
dev builds, which has been fixed in the 2018.1.x Have you tried to update?
It is also known that you can sometimes heal a small scale design by scaling
it up, while a scale-down is never a good idea. 




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