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[Efi Fogel <>]

You need to use CGAL::Exact_predicates_exact_constructions_kernel

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On Wed, Aug 7, 2013 at 5:17 PM, ax487 <> wrote:

Hello all,

I am trying to intersect two Polygon_2's using the CGAL::intersection
subroutine from CGAL/Boolean_set_operations_2.h.
Unfortunately, I get the following error:

terminate called after throwing an instance of
'CGAL::Precondition_exception'
  what():  CGAL ERROR: precondition violation!
Expr: ! _predP->is_valid() || comp_f(object, _predP->object) != SMALLER
File: /usr/include/CGAL/Multiset.h
Line: 2143

The error is deep inside the stack (what does that error message mean
anyways?), I am not at all familiar with the way that CGAL computes the
intersection of polygons (could you give me some literature reference)?
My Polygon_2 instances are:

0.150000000000000, 0.950000000000000
0.096033821847732, 0.896033821847732
0.150000000000000, 0.850000000000000
0.203966178152268, 0.803966178152268
0.250000000000000, 0.850000000000000
0.300000000000000, 0.900000000000000
0.250000000000000, 0.950000000000000
0.200000000000000, 1.000000000000000

and

0.150000000000000, 0.950000000000000
0.037954613459116, 0.945576109694670
0.150000000000000, 0.850000000000000
0.200000000000000, 0.800000000000000
0.250000000000000, 0.850000000000000
0.300000000000000, 0.900000000000000
0.250000000000000, 0.950000000000000
0.200000000000000, 1.000000000000000

I am using the CGAL::Exact_predicates_inexact_constructions_kernel and
CGAL 4.2. Could anyone explain to me what is going on and how I can get
this subroutine to work properly?

ax487

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