CGAL 4.7  2D Snap Rounding

#include <CGAL/Snap_rounding_traits_2.h>
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 kernelconcept, such as the Exact_predicates_exact_constructions_kernel
, or Cartesian<Gmpq>
.
This geometric kernel must provide an (arbitraryprecision) 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 doubleprecision 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 traitsconcept 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 nonincident edge can be slightly less than the guaranteed halfthe widthofapixel.