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[johnzjq <>]

Dear all,

I am using Nef_polyhedron with Exact_predicates_exact_constructions_kernel.
The following assertion was triggered when I was trying to convert a closed
polyhedron to Nef_polyhedron:

Error !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Error !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
CGAL error: assertion violation!
Expression : pre_prev->is_border() ||
!pe_prev->facet()->plane().is_degenerate()
File           : c:\program files
(x86)\cgal-3.7\include\cgal\nef_3\polyhedron_3_to_nef_3.h
Line          :219

The polyhedron is produced with MinkowskiSum and was regularized. I checked
the polyhedron and found one face that caused the assertion. The vertices of
the face is as follows:
(which have been convert to double)
vertex      x_coord           y_coord         z_coord
v1        -18219.3965   -12395.1836   -19974.9375
v2        -18185.4824   -12361.2695   -19974.9375
v3        -18215.4336   -12391.2207   -19974.9375

Questions:
1 Why did this face been judged as "degenerate", especially under an exact
kernal?
2 Is it proper to depoly simplification to eliminate such kind of face?

Any suggestions? 

Thanks in advance!

John
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