Re: [boost] Formal Review: Boost.Polygon starts today August 24, 2009

Subject: Re: [boost] Formal Review: Boost.Polygon starts today August 24, 2009
From: Simonson, Lucanus J (lucanus.j.simonson_at_[hidden])
Date: 2009-08-27 12:41:32

Andreas Fabri wrote:
> Hi Luke,
> 
> thank you for your explanations for the 45 degree case. You have a
> nice solution. I guess for the general case I have to read the
> BoostCon paper first. 
> 
> andreas

Thank you for saying so.

As requested, I haved added a test case for which CGAL fails to subversion

https://svn.boost.org/svn/boost/sandbox/gtl/forcgal.cpp

I appologize that the test case is rather large.  Expected output is:

 $$$$$$$$$$$$ RANDOM TEST $$$$$$$$$$$$$$$$
Square BOXX size: 6000 *************************
CGAL error: precondition violation!
Expr: compare_xy(cv1.right(), p) == LARGER && compare_xy(cv2.right(), p) == LARGER
File: /nfs/ltdn/disks/tcad_lmg_db_exchange_01/CGAL-3.3.1/include/CGAL/Arr_segment_traits_2.h
Line: 609
Explanation:
terminate called after throwing an instance of 'CGAL::Precondition_exception'
  what():  CGAL ERROR: precondition violation!
Expr: compare_xy(cv1.right(), p) == LARGER && compare_xy(cv2.right(), p) == LARGER
File: /nfs/ltdn/disks/tcad_lmg_db_exchange_01/CGAL-3.3.1/include/CGAL/Arr_segment_traits_2.h
Line: 609
Abort

This assertion in CGAL code looked to me like some condition that should be ensured by CGAL itself and is an internal error rather than a precondition violation.  My interpretation was that the wrong exception type was used.  I could be wrong, however, and if you find there was in fact something wrong with the polygon I produced I will eagerly fix my algorithm.  My intention was to implement a booleans algorithm with the weakest possible preconditions and the strongest possible postconditions.

Thanks,
Luke