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Voronoi Builder
The Voronoi builder is the event generator structure, that implements
the sweepline
algorithm,
scanning 2D space and spawning the two types of events: site
events and circle events. Each event is reported to the output data
structure builder.
The structure shares Voronoi name, as the events generated by it
provide
enough information to construct the Voronoi diagram of a set of points
and linear segments. The requirements for the coordinate type of
the input/output geometries, configured through the coordinate type
traits template argument, are the following:
 The input coordinate type (for input points and enpoints of
the input segments) is not required to be integral
(while it
still should be an integer type)
 The output coordinate type (for
Voronoi vertices) is required to be IEEE754 floating point type
Important
The users are encouraged to use the default static methods defined in
the voronoi.hpp
header for the Voronoi diagram construction. However it's also possible
to
use Voronoi builder explicitly, especially if the user wants to drop
the external dependencies such as MPL (metaprogramming library). The
following include set doesn't depend on any external headers
(except STL and boost/cstdint.hpp), even
the Boost.Polygon library:
#include
<voronoi_builder.hpp>
#include
<voronoi_diagram.hpp>
Declaration
Header: boost/polygon/voronoi_builder.hpp
template
<typename T,
typename CTT = detail::voronoi_ctype_traits<T>,
typename VP = detail::voronoi_predicates<CTT> >
class
voronoi_builder;
T
 specifies the coordinate type of the input geometries (points and
segments).
CTT
 defines the input/output coordinate type traits used by the Voronoi
predicates (VP).
VP
 the predicate kernel, that contains robust and
efficient predicates and functors.
The Voronoi builder data structure is ready to use from the box with
32bit signed integer input coordinate type. The user may extend the
input coordinate range to the other integer types (e.g. 64bit
integer), however this will also require manual setup of the
coordinate type traits. Default predicate kernel provides correct and
efficient predicates as long as types
defined by the coordinate type traits satisfy the requirements
explained at the end of this page. In case
those
requirements are not satisfied,
the proper predicate kernel
implementation is required.
Member Functions
voronoi_builder() 
Default
constructor. 
size_t insert_point(const int_type& x,
const int_type& y) 
Inserts a point object with
the specified coordinates into the Voronoi builder.
Returns index of the inserted point. 
size_t insert_segment(const int_type&
x1,
const int_type& y1,
const int_type& x2,
const int_type& y2) 
Inserts a segment object
with the specified coordinates into the Voronoi builder.
Returns index of the inserted segment. 
template
<typename OUTPUT>
void construct(OUTPUT* output)

Runs the sweepline
algorithm over the set of inserted geometries and generates site and
circle events to the OUTPUT data structure. It's the responsibility of
the
output data structure to process them. 
void
clear() 
Clears the
list of the inserted geometries. Sets the input geometry index to
zero. 
Voronoi Coordinate Type Traits
The library provides the default coordinate type traits
specialization for the
32bit signed integer type:
template <typename T>
struct voronoi_ctype_traits;
template <>
struct voronoi_ctype_traits<int32> {
typedef int32 int_type;
typedef int64 int_x2_type;
typedef uint64 uint_x2_type;
typedef extended_int<128> big_int_type;
typedef fpt64 fpt_type;
typedef extended_exponent_fpt<fpt_type>
efpt_type;
typedef ulp_comparison<fpt_type> ulp_cmp_type;
typedef type_converter_fpt to_fpt_converter_type;
typedef type_converter_efpt to_efpt_converter_type;
};
One
of the most important features of the library is that Voronoi builder
output geometries are constructed within defined relative error (64
machine epsilons). That means, the more mantissa bits the user provided
fpt_type has, the better precision of the output geometries will be. In
order for the user defined traits to be consistent with the default
Voronoi builder predicate kernel user should define the following set
of traits (the assumption is made that input geometries have
Xbit signed integer coordinate type):
int_type

At least Xbit signed
integer type. 
int_x2_type

At least 2Xbit signed
integer type. 
uint_x2_type

At least 2Xbit unsigned
integer type. 
big_int_type

At least 8Xbit signed
integer type if input dataset contains only points.
At least 64Xbit signed integer type if input dataset contains
segments. 
fpt_type

IEEE754 floating point
type, with mantissa at least (X+16) bits and exponent able to handle
32Xbit unsigned integer type. 
efpt_type

IEEE754 floating point
type, with mantissa at least (X+16) bits and exponent able to handle
64Xbit unsigned integer type. 
ulp_cmp_type

Ulp comparison structure,
that checks if two fpt_type values are within the given ulp range
(relative error range). 
to_fpt_converter_type

Type converter structure,
that converts any of the integer types above plus efpt_type to the
fpt_type using operator(). 
to_efpt_converter_type

Type converter structure,
that converts any of the integer types above to the efpt_type using
operator(). 
Notes:
 Four different integer types are used (instead of a single
big_int_type) to slightly improve algorithm performance and memory
usage.
 As the maximum required size of the big_int_type is known
in advance, it's possible to use fixed, stack allocated, multiprecision
integer type.
 Two separate floatingpoint types are defined, because for
the input geometries
with
32bit signed integer coordinates, double type won't be able to handle
2048bit (64 chunks of 32 bits each) integers, as they will
overflow its exponent. On the
gcc compiler it's possible to use 80bit long doubles for both fpt
types, however this is not supported by the MSVC compiler.
 efpt_type and to_efpt_converter_type are not used to
construct the Voronoi diagram of a set of points (mock implementation
will work).
 For an example of the user defined coordinate type traits
check the advanced Voronoi
tutorial.
