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[Manoj Bist <>]

 have attached a testcase that illustrates the issue. Its a cpp file that you can compile to reproduce the issue. 

Please note that the input is valid. Approximate decomposition works correctly. Optimal decomposition fails in CGAL_partition_postcondition. Please do not be confused by the name of CGAL ERROR: precondition violation. It is actually failing in the post condition, where in it verifies that the decomposition is correct.

1. I've verified that the input polygon is  a simple counter clockwise polygon. I have put the following two asserts to ensure this invariant.

 assert(CGAL::is_simple_2(polygon.vertices_begin(), polygon.vertices_end(), Traits()));
assert(CGAL::orientation_2(polygon.vertices_begin(), polygon.vertices_end(), Traits()) == CGAL::COUNTERCLOCKWISE);

 assert(!hasDuplicatePoints(polygon));

2. To test the logical correctness for the input polygon, I have also done the following.

I've identified a point that is outside the input polygon. A point that is outside the input polygon should be outside all the polygons in convex decomposition.

Approximate decomposition passes this.

3. First I run the approximate decomposition CGAL::approx_convex_partition_2. It works as expected.

4. This post condition fails for optimal decomposition.

      CGAL_partition_postcondition(
             convex_partition_is_valid_2(polygon.begin(), polygon.end(),
                                      res.output_so_far_begin(),
                                      res.output_so_far_end(), traits)

Attachment: testcase.cpp
Description: Binary data