The class *Snap_rounding_traits_2<Kernel>* is a model of the
*SnapRoundingTraits_2* concept, and is the only traits class supplied
with the package.
This class should be instantiated with an exact geometric kernel that conforms
to the CGAL kernel-concept, such as the
*Cartesian<gmpq>* kernel.

This geometric kernel must provide an (arbitrary-precision) rational number type
(*FT*), *Point_2*, *Segment_2* and *Iso_rectangle_2*.
It should be possible to cast numbers of the number type *FT* to
double-precision representation. That is, the function
*CGAL::to_double(FT)* must be supported.

The *CGAL::to_double()* function is used to implement the operation that
rounds the coordinates of a point to a center of a pixel. This operation is one
of the traits-concept requirement. The coordinates are converted to double,
rounded down to the nearest grid point, and finally adjusted to lie on a center
of a pixel. Notice that if
*CGAL::to_double()* returns the closet value, then when it rounds up a given
coordinate, the resulting ISR, may be imprecise, and the distance between some
vertex and a non-incident edge can be slightly less than the guaranteed
half-the width-of-a-pixel.

*#include <CGAL/Snap_rounding_traits_2.h>*

CGAL Open Source Project.
Release 3.2.1.
13 July 2006.