CGAL users discussion list

[Hamid G <>]

Hi

What method would you suggest to use in order to write coordinates of 
points from an exact kernel to a file on hard disk so that when we read 
it later on we won't use any precision/information ?

I am using different modules from CGAL that don't support a common 
kernel. So after using each module I write the results to a .OFF file 
using provided iostream methods. And then I read that file in the next 
module.

typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
CGAL::Polyhedron_3<Kernel> shell;
ofstream fid("out.off")
fid << shell;


I am getting random assertion failures here and there in the modules I 
am using, similar to this:

terminate called after throwing an instance of 
'CGAL::Precondition_exception'
  what():  CGAL ERROR: precondition violation!
Expr: ! k.is_degenerate_3_object()(t)
File: /home/hamid/local/include/CGAL/Triangle_3_Segment_3_do_intersect.h

This doesn't happen all the time for the same input and settings!
So I am guessing assertion failures are somehow related to rounding off 
the coordinates in file I/O operations.

This is a general view of which modules I am using from CGAL:

1- Surface_mesh with gray scale image as input (not sure which kernel 
'Surface_mesh_default_triangulation_3' is using)

2- Then the resulting surface mesh from 1 is used in Nef_3 for a 
subtraction boolean operation with another surface mesh. (here I use 
'Exact_predicates_exact_constructions_kernel')

3- The resulting surface mesh from 2 is refined using 
Exact_predicates_inexact_constructions_kernel in 'Subdivision_method_3'

4- The resulting surface from 3 is then fed to tetrahedral mesh 
generator which uses Exact_predicates_inexact_constructions_kernel with 
'Robust_intersection_traits_3'

Am I using the right kernel ? Any suggestion about which kernels are 
better fit for this workflow assuming that I am using file I/O to send 
the data between these modules.

thanks in advance,
Hamid G