CGAL users discussion list

[Efi Fogel <>]

If you are using an exact predicate and exact construction kernel, then it seems like a bug; either in the union operation (join) or the validity check.

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On 7 April 2017 at 04:51, Ch'Gans <> wrote:

Hi there,

Every now and then when I join polygons into a polygon set, the
polygon set becomes invalid.

To make sure i am not inserting invalid polygon, i have tried to check
them all individually before calling join(), eg:

std::vector<Polygon_2> allPolygons;
buildPolygons(allPolygons);
Polygon_set_2 S;
for (const auto &poly: allPolygons)
   if (!CGAL::is_valid_unknown_polygon(poly, S.traits()))
     qWarning() << "Found invalid input polygon";
S.join(allPolygons.begin(), allPolygons.end());
if (!S.is_valid()) {
  qDebug() << "Polygon set invalid after inserting all polygons";
}

When i run the above code, i get no "Found invalid input polygon"
warning, yet i get a final "Polygon set invalid after inserting all
polygons" along with this CGAL message:

CGAL warning: check violation!
_expression_ : false
File : /usr/include/CGAL/Arrangement_2/Arrangement_on_surface_2_global.h
Line : 1407
Explanation: An inner component is located in the wrong face.
Refer to the bug-reporting instructions at http://www.cgal.org/bug_report.html

Is this a bug, or am I not doing the right checks against the input polygons?

Chris

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