CGAL users discussion list

["Ch'Gans" <>]

On 4 March 2017 at 00:28, Efi Fogel 
<>
 wrote:
> Could you please attach a small program that reproduces the problem.

I used that approach (reproduce the problem  with a small program),
and realised that it worked, always. So I dag deeper and pin-pointed
the problem, the root cause was a use-after-free in another part of my
application! On top of that i've switched to an exact construction
kernel, so now everything seems to work nicely.

Thanks,
Chris

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> On 3 March 2017 at 04:53, Ch'Gans 
> <>
>  wrote:
>>
>> Hi there,
>>
>> I am trying to insert segment whose end points correspond to existing
>> vertices.
>> Here is the use case that trigger an assertion:
>> - insert 4 segment to form a 4 sided face 'F'
>> - insert a segment S1 to form the first diagonal of 'F' (causing F to
>> be split in 2)
>> - insert a segment S2 to form the second diagonal of 'F' (visually
>> speaking)
>>
>> The 2 diagonals are inserted using
>> "insert_at_vertices(Segment(v1->point(), v2->point()), v1, v2)"
>>
>> When inserting the second diagonal i get an assertion:
>> ------------------------------
>> terminate called after throwing an instance of
>> 'CGAL::Precondition_exception'
>> what(): CGAL ERROR: precondition violation!
>> Expr: f == f2
>> File:
>> /usr/local/include/CGAL/Arrangement_2/Arrangement_on_surface_2_impl.h
>> Line: 2667
>> Explanation: The two halfedges must share the same incident face
>> ------------------------------
>>
>> I get the same results, using CGAL-4.8.1-1build1 and CGAL from git.
>>
>> Looking at the documentation i cannot see this precondition listed,
>> here is the list of preconditions:
>> 1. The interior of c is disjoint from all existing arrangement
>> vertices and edges.
>> 2. c must not be an unbounded curve.
>> 3. v1 and v2 are associated with c's endpoints.
>> 4. If v1 and v2 are already connected by an edge, this edge represents
>> an x-monotone curve that is interior-disjoint from c).
>>
>> I'm clearly not violating 2, 3 and 4. Am I violating 1? If so, could
>> someone shed some light on the meaning of it and what it implies?
>> If not, then shouldn't the documentation be updated? I'm happy to make
>> the change and do a pull request for it.
>>
>> Thanks,
>> Chris
>>
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>