CGAL users discussion list

[Matthijs Sypkens Smit <>]

Hi,

I'm wondering about the following: I know the construction of a 
circumcenter (of 4 points) is only possible when the points are not 
collinear. However, when using a 
Exact_predicates_inexact_constructions_kernel I encounter cases where:
- coplanar_orientation() returns COLLINEAR, but the construction does not 
fail and returns a point,
- coplanar_orientation() does not return COLLINEAR, but the circumcenter 
construction does end in an assertion failure.

Are both these cases to be expected? In particular the last surprised me, 
since I was hoping to 'catch' the assertion failure, by testing in 
advance, but now it seems that this does not generally work.

Is it just plain impossible to construct circumcenters without getting 
assertion failures using my choice of kernel, or are there ways around 
this (by testing beforehand)?


btw;I have tried to check that using a 
Exact_predicates_exact_constructions_kernel prevents the problem from 
happening, but I have little experience with this kernel as of yet. I'm 
getting
  CGAL error: assertion violation!
  Expr: !(i>s)
  File: /user/CGAL-3.3/include/CGAL/Interval_nt.h
  Line: 77
  Explanation: Variable used before being initialized (or CGAL bug)
but so far I cannot seem to find the cause of the problem. I do believe 
that all variables involved have actually been initialized.


-- 
Matthijs Sypkens Smit