geos::algorithm::hull::ConcaveHullOfPolygons Class Reference

#include <ConcaveHullOfPolygons.h>

Public Member Functions
	ConcaveHullOfPolygons (const Geometry *geom)
void	setMaximumEdgeLength (double edgeLength)
void	setMaximumEdgeLengthRatio (double edgeLengthRatio)
void	setHolesAllowed (bool p_isHolesAllowed)
void	setTight (bool p_isTight)
std::unique_ptr< Geometry >	getHull ()
std::unique_ptr< Geometry >	getFill ()

Static Public Member Functions
static std::unique_ptr< Geometry >	concaveHullByLength (const Geometry *polygons, double maxLength)
static std::unique_ptr< Geometry >	concaveHullByLength (const Geometry *polygons, double maxLength, bool isTight, bool isHolesAllowed)
static std::unique_ptr< Geometry >	concaveHullByLengthRatio (const Geometry *polygons, double lengthRatio)
static std::unique_ptr< Geometry >	concaveHullByLengthRatio (const Geometry *polygons, double lengthRatio, bool isTight, bool isHolesAllowed)
static std::unique_ptr< Geometry >	concaveFillByLength (const Geometry *polygons, double maxLength)
static std::unique_ptr< Geometry >	concaveFillByLengthRatio (const Geometry *polygons, double lengthRatio)

Detailed Description

Constructs a concave hull of a set of polygons, respecting the polygons as constraints. A concave hull is a possibly non-convex polygon containing all the input polygons. A given set of polygons has a sequence of hulls of increasing concaveness, determined by a numeric target parameter. The computed hull "fills the gap" between the polygons, and does not intersect their interior.

The concave hull is constructed by removing the longest outer edges of the Delaunay Triangulation of the space between the polygons, until the target criterion parameter is reached.

The target criteria are:

• Maximum Edge Length - the length of the longest edge between the polygons is no larger than this value.
• Maximum Edge Length Ratio - determine the Maximum Edge Length as a fraction of the difference between the longest and shortest edge lengths between the polygons. This normalizes the Maximum Edge Length to be scale-free. A value of 1 produces the convex hull; a value of 0 produces the original polygons.

The preferred criterion is the Maximum Edge Length Ratio, since it is scale-free and local (so that no assumption needs to be made about the total amount of concaveness present).

Optionally the concave hull can be allowed to contain holes, via setHolesAllowed().

The hull can be specified as being "tight", which means it follows the outer boundaries of the input polygons.

The input polygons must form a valid MultiPolygon (i.e. they must be non-overlapping).

Author

Martin Davis

Constructor & Destructor Documentation

ConcaveHullOfPolygons()

geos::algorithm::hull::ConcaveHullOfPolygons::ConcaveHullOfPolygons

(

const Geometry *

geom

)

Creates a new instance for a given geometry.

Parameters

geom	the input geometry

Member Function Documentation

concaveFillByLength()

static std::unique_ptr<Geometry> geos::algorithm::hull::ConcaveHullOfPolygons::concaveFillByLength ( const Geometry *  polygons, double  maxLength  )

static

Computes a concave fill area between a set of polygons, using the target criterion of maximum edge length.

Parameters

polygons	the input polygons
maxLength	the target maximum edge length

Returns

the concave fill

concaveFillByLengthRatio()

static std::unique_ptr<Geometry> geos::algorithm::hull::ConcaveHullOfPolygons::concaveFillByLengthRatio ( const Geometry *  polygons, double  lengthRatio  )

static

Computes a concave fill area between a set of polygons, using the target criterion of maximum edge length ratio.

Parameters

polygons	the input polygons
lengthRatio	the target maximum edge length ratio

Returns

the concave fill

concaveHullByLength() [1/2]

static std::unique_ptr<Geometry> geos::algorithm::hull::ConcaveHullOfPolygons::concaveHullByLength ( const Geometry *  polygons, double  maxLength  )

static

Computes a concave hull of set of polygons using the target criterion of maximum edge length.

Parameters

polygons	the input polygons
maxLength	the target maximum edge length

Returns

the concave hull

concaveHullByLength() [2/2]

static std::unique_ptr<Geometry> geos::algorithm::hull::ConcaveHullOfPolygons::concaveHullByLength ( const Geometry *  polygons, double  maxLength, bool  isTight, bool  isHolesAllowed  )

static

Computes a concave hull of set of polygons using the target criterion of maximum edge length, and allowing control over whether the hull boundary is tight and can contain holes.

Parameters

polygons	the input polygons
maxLength	the target maximum edge length
isTight	true if the hull should be tight to the outside of the polygons
isHolesAllowed	true if holes are allowed in the hull polygon

Returns

the concave hull

concaveHullByLengthRatio() [1/2]

static std::unique_ptr<Geometry> geos::algorithm::hull::ConcaveHullOfPolygons::concaveHullByLengthRatio ( const Geometry *  polygons, double  lengthRatio  )

static

Computes a concave hull of set of polygons using the target criterion of maximum edge length ratio.

Parameters

polygons	the input polygons
lengthRatio	the target maximum edge length ratio

Returns

the concave hull

concaveHullByLengthRatio() [2/2]

static std::unique_ptr<Geometry> geos::algorithm::hull::ConcaveHullOfPolygons::concaveHullByLengthRatio ( const Geometry *  polygons, double  lengthRatio, bool  isTight, bool  isHolesAllowed  )

static

Computes a concave hull of set of polygons using the target criterion of maximum edge length ratio, and allowing control over whether the hull boundary is tight and can contain holes.

Parameters

polygons	the input polygons
lengthRatio	the target maximum edge length ratio
isTight	true if the hull should be tight to the outside of the polygons
isHolesAllowed	true if holes are allowed in the hull polygon

Returns

the concave hull

getFill()

std::unique_ptr<Geometry> geos::algorithm::hull::ConcaveHullOfPolygons::getFill

(

)

Gets the concave fill, which is the area between the input polygons, subject to the concaveness control parameter.

Returns

the concave fill

getHull()

std::unique_ptr<Geometry> geos::algorithm::hull::ConcaveHullOfPolygons::getHull

(

)

Gets the computed concave hull.

Returns

the concave hull

setHolesAllowed()

void geos::algorithm::hull::ConcaveHullOfPolygons::setHolesAllowed

(

bool

p_isHolesAllowed

)

Sets whether holes are allowed in the concave hull polygon.

Parameters

p_isHolesAllowed

true if holes are allowed in the result

setMaximumEdgeLength()

void geos::algorithm::hull::ConcaveHullOfPolygons::setMaximumEdgeLength

(

double

edgeLength

)

Sets the target maximum edge length for the concave hull. The length value must be zero or greater.

• The value 0.0 produces the input polygons.
• Larger values produce less concave results. Above a certain large value the result is the convex hull of the input.

The edge length ratio provides a scale-free parameter which is intended to produce similar concave results for a variety of inputs.

Parameters

edgeLength

a non-negative length

setMaximumEdgeLengthRatio()

void geos::algorithm::hull::ConcaveHullOfPolygons::setMaximumEdgeLengthRatio

(

double

edgeLengthRatio

)

Sets the target maximum edge length ratio for the concave hull. The edge length ratio is a fraction of the difference between the longest and shortest edge lengths in the Delaunay Triangulation of the area between the input polygons. (Roughly speaking, it is a fraction of the difference between the shortest and longest distances between the input polygons.) It is a value in the range 0 to 1.

• The value 0.0 produces the original input polygons.
• The value 1.0 produces the convex hull.

Parameters

edgeLengthRatio

a length factor value between 0 and 1

setTight()

void geos::algorithm::hull::ConcaveHullOfPolygons::setTight

(

bool

p_isTight

)

Sets whether the boundary of the hull polygon is kept tight to the outer edges of the input polygons.

Parameters

p_isTight

true if the boundary is kept tight

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The documentation for this class was generated from the following file:

• ConcaveHullOfPolygons.h