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geos::Geometry Class Reference

Basic implementation of Geometry, constructed and destructed by GeometryFactory. More...

#include <geos.h>

Inheritance diagram for geos::Geometry:

geos::GeometryCollection geos::LineString geos::Point geos::Polygon geos::MultiLineString geos::MultiPoint geos::MultiPolygon geos::LinearRing List of all members.

Public Member Functions

 Geometry (const GeometryFactory *factory)
 Construct a geometry with the given GeometryFactory. Will keep a reference to the factory, so don't delete it until al Geometry objects referring to it are deleted.
virtual ~Geometry ()
virtual Geometryclone () const =0
 Make a deep-copy of this Geometry.
const GeometryFactorygetFactory () const
 Gets the factory which contains the context in which this geometry was created.
void setUserData (void *newUserData)
 A simple scheme for applications to add their own custom data to a Geometry. An example use might be to add an object representing a Coordinate Reference System.
void * getUserData ()
 Gets the user data object for this geometry, if any.
virtual const PrecisionModelgetPrecisionModel () const
 Get the PrecisionModel used to create this Geometry.
virtual const CoordinategetCoordinate () const =0
 Returns a vertex of this Geometry.
virtual CoordinateSequencegetCoordinates () const =0
 Returns this Geometry vertices. Caller takes ownership of the returned object.
virtual int getNumPoints () const =0
 Returns the count of this Geometrys vertices.
virtual bool isSimple () const =0
 Returns false if the Geometry not simple.
virtual string getGeometryType () const =0
 Return a string representation of this Geometry type.
virtual GeometryTypeId getGeometryTypeId () const =0
 Return an integer representation of this Geometry type.
virtual bool isValid () const
 Tests the validity of this Geometry.
virtual bool isEmpty () const =0
 Returns whether or not the set of points in this Geometry is empty.
virtual int getDimension () const =0
 Returns the dimension of this Geometry (0=point, 1=line, 2=surface).
virtual GeometrygetBoundary () const =0
 Returns the boundary, or the empty geometry if this Geometry is empty.
virtual int getBoundaryDimension () const =0
 Returns the dimension of this Geometrys inherent boundary.
virtual GeometrygetEnvelope () const
 Returns this Geometrys bounding box.
virtual const EnvelopegetEnvelopeInternal () const
 Returns the minimum and maximum x and y values in this Geometry, or a null Envelope if this Geometry is empty.
virtual bool disjoint (const Geometry *other) const
 Returns true if the DE-9IM intersection matrix for the two Geometrys is FF*FF****.
virtual bool touches (const Geometry *other) const
 Returns true if the DE-9IM intersection matrix for the two Geometrys is FT*******, F**T***** or F***T****.
virtual bool intersects (const Geometry *g) const
 Returns true if disjoint returns false.
virtual bool crosses (const Geometry *g) const
 Returns true if the DE-9IM intersection matrix for the two Geometrys is T*T****** (for a point and a curve, a point and an area or a line and an area) 0******** (for two curves).
virtual bool within (const Geometry *g) const
 Returns true if the DE-9IM intersection matrix for the two Geometrys is T*F**F***.
virtual bool contains (const Geometry *g) const
 Returns true if other.within(this) returns true.
virtual bool overlaps (const Geometry *g) const
 Returns true if the DE-9IM intersection matrix for the two Geometrys is T*T***T** (for two points or two surfaces) 1*T***T** (for two curves).
virtual bool relate (const Geometry *g, string intersectionPattern) const
 Returns true if the elements in the DE-9IM intersection matrix for the two Geometrys match the elements in intersectionPattern.
virtual IntersectionMatrix * relate (const Geometry *g) const
 Returns the DE-9IM intersection matrix for the two Geometrys.
virtual bool equals (const Geometry *g) const
 Returns true if the DE-9IM intersection matrix for the two Geometrys is T*F**FFF*.
virtual string toString () const
 Returns the Well-known Text representation of this Geometry.
virtual Geometrybuffer (double distance) const
 Returns a buffer region around this Geometry having the given width.
virtual Geometrybuffer (double distance, int quadrantSegments) const
 Returns a buffer region around this Geometry having the given width and with a specified number of segments used to approximate curves.
virtual GeometryconvexHull () const
 Returns the smallest convex Polygon that contains all the points in the Geometry.
virtual Geometryintersection (const Geometry *other) const
 Returns a Geometry representing the points shared by this Geometry and other.
virtual GeometryUnion (const Geometry *other) const
 Returns a Geometry representing all the points in this Geometry and other.
virtual Geometrydifference (const Geometry *other) const
 Returns a Geometry representing the points making up this Geometry that do not make up other.
virtual GeometrysymDifference (const Geometry *other) const
 Returns a set combining the points in this Geometry not in other, and the points in other not in this Geometry.
virtual bool equalsExact (const Geometry *other, double tolerance) const =0
 Returns true if the two Geometrys are exactly equal, up to a specified tolerance.
virtual void normalize ()=0
 Converts this Geometry to normal form (or canonical form).
virtual double distance (const Geometry *g) const
 Returns the minimum distance between this Geometry and the Geometry g.
virtual double getArea () const
 Returns the area of this Geometry.
virtual double getLength () const
 Returns the length of this Geometry.
virtual bool isWithinDistance (const Geometry *geom, double cDistance)
 Tests whether the distance from this Geometry to another is less than or equal to a specified value.
virtual PointgetCentroid () const
 Computes the centroid of this Geometry.
virtual PointgetInteriorPoint ()
 Computes an interior point of this Geometry.
virtual void geometryChanged ()
void geometryChangedAction ()

Protected Member Functions

virtual bool isEquivalentClass (const Geometry *other) const
 Returns whether the two Geometrys are equal, from the point of view of the equalsExact method.
GeometrytoInternalGeometry (const Geometry *g) const

Static Protected Member Functions

static bool hasNonEmptyElements (const vector< Geometry * > *geometries)
 Returns true if the array contains any non-empty Geometrys.
static bool hasNullElements (const CoordinateSequence *list)
 Returns true if the CoordinateSequence contains any null elements.
static bool hasNullElements (const vector< Geometry * > *lrs)
 Returns true if the vector contains any null elements.

Detailed Description

Basic implementation of Geometry, constructed and destructed by GeometryFactory.

clone returns a deep copy of the object. Use GeometryFactory to construct.

Binary Predicates

Because it is not clear at this time what semantics for spatial analysis methods involving GeometryCollections would be useful, GeometryCollections are not supported as arguments to binary predicates (other than convexHull) or the relate method.

Set-Theoretic Methods

The spatial analysis methods will return the most specific class possible to represent the result. If the result is homogeneous, a Point, LineString, or Polygon will be returned if the result contains a single element; otherwise, a MultiPoint, MultiLineString, or MultiPolygon will be returned. If the result is heterogeneous a GeometryCollection will be returned.

Because it is not clear at this time what semantics for set-theoretic methods involving GeometryCollections would be useful, GeometryCollections are not supported as arguments to the set-theoretic methods.

Representation of Computed Geometries

The SFS states that the result of a set-theoretic method is the "point-set" result of the usual set-theoretic definition of the operation (SFS 3.2.21.1). However, there are sometimes many ways of representing a point set as a Geometry.

The SFS does not specify an unambiguous representation of a given point set returned from a spatial analysis method. One goal of JTS is to make this specification precise and unambiguous. JTS will use a canonical form for Geometrys returned from spatial analysis methods. The canonical form is a Geometry which is simple and noded:

This definition implies that non-simple geometries which are arguments to spatial analysis methods must be subjected to a line-dissolve process to ensure that the results are simple.

Constructed Points And The Precision Model

The results computed by the set-theoretic methods may contain constructed points which are not present in the input Geometry s. These new points arise from intersections between line segments in the edges of the input Geometrys. In the general case it is not possible to represent constructed points exactly. This is due to the fact that the coordinates of an intersection point may contain twice as many bits of precision as the coordinates of the input line segments. In order to represent these constructed points explicitly, JTS must truncate them to fit the PrecisionModel.

Unfortunately, truncating coordinates moves them slightly. Line segments which would not be coincident in the exact result may become coincident in the truncated representation. This in turn leads to "topology collapses" -- situations where a computed element has a lower dimension than it would in the exact result.

When JTS detects topology collapses during the computation of spatial analysis methods, it will throw an exception. If possible the exception will report the location of the collapse.

equals(Object) and hashCode are not overridden, so that when two topologically equal Geometries are added to HashMaps and HashSets, they remain distinct. This behaviour is desired in many cases.


Constructor & Destructor Documentation

geos::Geometry::~Geometry  )  [virtual]
 

Destroy Geometry and all components


Member Function Documentation

Geometry * geos::Geometry::buffer double  distance,
int  quadrantSegments
const [virtual]
 

Returns a buffer region around this Geometry having the given width and with a specified number of segments used to approximate curves.

Returns a buffer region around this Geometry having the given width and with a specified number of segments used to approximate curves. The buffer of a Geometry is the Minkowski sum of the Geometry with a disc of radius distance. Curves in the buffer polygon are approximated with line segments. This method allows specifying the accuracy of that approximation.

Parameters:
distance the width of the buffer, interpreted according to the PrecisionModel of the Geometry
quadrantSegments the number of segments to use to approximate a quadrant of a circle
Returns:
all points whose distance from this Geometry are less than or equal to distance

double geos::Geometry::distance const Geometry other  )  const [virtual]
 

Returns the minimum distance between this Geometry and the Geometry g.

Returns the minimum distance between this Geometry and the other Geometry

Parameters:
other the Geometry from which to compute the distance

void geos::Geometry::geometryChanged  )  [virtual]
 

Notifies this Geometry that its Coordinates have been changed by an external party (using a CoordinateFilter, for example). The Geometry will flush and/or update any information it has cached (such as its Envelope ).

void geos::Geometry::geometryChangedAction  ) 
 

Notifies this Geometry that its Coordinates have been changed by an external party. When geometryChanged is called, this method will be called for this Geometry and its component Geometries.

See also:
apply(GeometryComponentFilter *)

double geos::Geometry::getArea  )  const [virtual]
 

Returns the area of this Geometry.

Returns the area of this Geometry. Areal Geometries have a non-zero area. They override this function to compute the area. Others return 0.0

Returns:
the area of the Geometry

Reimplemented in geos::GeometryCollection, and geos::Polygon.

Point * geos::Geometry::getCentroid  )  const [virtual]
 

Computes the centroid of this Geometry.

Computes the centroid of this Geometry. The centroid is equal to the centroid of the set of component Geometrys of highest dimension (since the lower-dimension geometries contribute zero "weight" to the centroid)

Returns:
a Point which is the centroid of this Geometry

const GeometryFactory * geos::Geometry::getFactory  )  const
 

Gets the factory which contains the context in which this geometry was created.

Returns:
the factory for this geometry

Point * geos::Geometry::getInteriorPoint  )  [virtual]
 

Computes an interior point of this Geometry.

Computes an interior point of this Geometry. An interior point is guaranteed to lie in the interior of the Geometry, if it possible to calculate such a point exactly. Otherwise, the point may lie on the boundary of the geometry.

Returns:
a Point which is in the interior of this Geometry

double geos::Geometry::getLength  )  const [virtual]
 

Returns the length of this Geometry.

Returns the length of this Geometry. Linear geometries return their length. Areal geometries return their perimeter. They override this function to compute the area. Others return 0.0

Returns:
the length of the Geometry

Reimplemented in geos::GeometryCollection, geos::LineString, and geos::Polygon.

void * geos::Geometry::getUserData  ) 
 

Gets the user data object for this geometry, if any.

Returns:
the user data object, or null if none set

bool geos::Geometry::isValid  )  const [virtual]
 

Tests the validity of this Geometry.

Subclasses provide their own definition of "valid".

Returns:
true if this Geometry is valid
See also:
IsValidOp

bool geos::Geometry::isWithinDistance const Geometry geom,
double  cDistance
[virtual]
 

Tests whether the distance from this Geometry to another is less than or equal to a specified value.

Tests whether the distance from this Geometry to another is less than or equal to a specified value.

Parameters:
geom the Geometry to check the distance to
cDistance the distance value to compare
Returns:
true if the geometries are less than distance apart.

bool geos::Geometry::relate const Geometry g,
string  intersectionPattern
const [virtual]
 

Returns true if the elements in the DE-9IM intersection matrix for the two Geometrys match the elements in intersectionPattern.

IntersectionPattern elements may be: 0 1 2 T ( = 0, 1 or 2) F ( = -1) * ( = -1, 0, 1 or 2).

For more information on the DE-9IM, see the OpenGIS Simple Features Specification.

void geos::Geometry::setUserData void *  newUserData  ) 
 

A simple scheme for applications to add their own custom data to a Geometry. An example use might be to add an object representing a Coordinate Reference System.

Note that user data objects are not present in geometries created by construction methods.

Parameters:
newUserData an object, the semantics for which are defined by the application using this Geometry

Geometry * geos::Geometry::toInternalGeometry const Geometry g  )  const [protected]
 

The GEOS algorithms assume that Geometry::getCoordinate() and getCoordinates are fast, which may not be the case if the CoordinateSequence is not a DefaultCoordinateSequence (e.g. if it were implemented using separate arrays for the x- and y-values), in which case frequent construction of Coordinates takes up much space and time. To solve this performance problem, toInternalGeometry converts the Geometry to a DefaultCoordinateSequence implementation before sending it to the JTS algorithms.


The documentation for this class was generated from the following files:
Generated on Tue Jan 10 01:37:53 2006 for GEOS by  doxygen 1.4.4