com.revolsys.jts.planargraph

Class DirectedEdge

java.lang.Object

com.revolsys.jts.planargraph.GraphComponent

com.revolsys.jts.planargraph.DirectedEdge

All Implemented Interfaces:

Comparable

Direct Known Subclasses:

LineMergeDirectedEdge

public class DirectedEdge
extends GraphComponent
implements Comparable

Represents a directed edge in a PlanarGraph. A DirectedEdge may or may not have a reference to a parent Edge (some applications of planar graphs may not require explicit Edge objects to be created). Usually a client using a PlanarGraph will subclass DirectedEdge to add its own application-specific data and methods.

Version:

1.7

Field Summary

Fields

Modifier and Type	Field and Description
protected double	angle
protected boolean	edgeDirection
protected Node	from
protected Point	p0
protected Point	p1
protected Edge	parentEdge
protected int	quadrant
protected DirectedEdge	sym
protected Node	to

Fields inherited from class com.revolsys.jts.planargraph.GraphComponent

isMarked, isVisited

Constructor Summary

Constructors

Constructor and Description
DirectedEdge(Node from, Node to, Point directionPt, boolean edgeDirection) Constructs a DirectedEdge connecting the from node to the to node.

Method Summary

Methods

Modifier and Type	Method and Description
int	compareDirection(DirectedEdge e) Returns 1 if this DirectedEdge has a greater angle with the positive x-axis than b", 0 if the DirectedEdges are collinear, and -1 otherwise.
int	compareTo(Object obj) Returns 1 if this DirectedEdge has a greater angle with the positive x-axis than b", 0 if the DirectedEdges are collinear, and -1 otherwise.
double	getAngle() Returns the angle that the start of this DirectedEdge makes with the positive x-axis, in radians.
Point	getCoordinate() Returns the coordinate of the from-node.
Point	getDirectionPt() Returns a point to which an imaginary line is drawn from the from-node to specify this DirectedEdge's orientation.
Edge	getEdge() Returns this DirectedEdge's parent Edge, or null if it has none.
boolean	getEdgeDirection() Returns whether the direction of the parent Edge (if any) is the same as that of this Directed Edge.
Node	getFromNode() Returns the node from which this DirectedEdge leaves.
int	getQuadrant() Returns 0, 1, 2, or 3, indicating the quadrant in which this DirectedEdge's orientation lies.
DirectedEdge	getSym() Returns the symmetric DirectedEdge -- the other DirectedEdge associated with this DirectedEdge's parent Edge.
Node	getToNode() Returns the node to which this DirectedEdge goes.
boolean	isRemoved() Tests whether this directed edge has been removed from its containing graph
void	print(PrintStream out) Prints a detailed string representation of this DirectedEdge to the given PrintStream.
void	setEdge(Edge parentEdge) Associates this DirectedEdge with an Edge (possibly null, indicating no associated Edge).
void	setSym(DirectedEdge sym) Sets this DirectedEdge's symmetric DirectedEdge, which runs in the opposite direction.
static List	toEdges(Collection dirEdges) Returns a List containing the parent Edge (possibly null) for each of the given DirectedEdges.

Methods inherited from class com.revolsys.jts.planargraph.GraphComponent

getComponentWithVisitedState, getContext, getData, isMarked, isVisited, setContext, setData, setMarked, setMarked, setVisited, setVisited

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

parentEdge

protected Edge parentEdge

from

protected Node from

to

protected Node to

p0

protected Point p0

p1

protected Point p1

sym

protected DirectedEdge sym

edgeDirection

protected boolean edgeDirection

quadrant

protected int quadrant

angle

protected double angle

Constructor Detail

DirectedEdge

public DirectedEdge(Node from,
            Node to,
            Point directionPt,
            boolean edgeDirection)

Constructs a DirectedEdge connecting the from node to the to node.

Parameters:

directionPt - specifies this DirectedEdge's direction vector (determined by the vector from the from node to directionPt)

edgeDirection - whether this DirectedEdge's direction is the same as or opposite to that of the parent Edge (if any)

Method Detail

toEdges

public static List toEdges(Collection dirEdges)

Returns a List containing the parent Edge (possibly null) for each of the given DirectedEdges.

compareDirection

public int compareDirection(DirectedEdge e)

Returns 1 if this DirectedEdge has a greater angle with the positive x-axis than b", 0 if the DirectedEdges are collinear, and -1 otherwise.

Using the obvious algorithm of simply computing the angle is not robust, since the angle calculation is susceptible to roundoff. A robust algorithm is:

• first compare the quadrants. If the quadrants are different, it it trivial to determine which vector is "greater".
• if the vectors lie in the same quadrant, the robust CGAlgorithms#computeOrientation(Point, Point, Point) function can be used to decide the relative orientation of the vectors.

compareTo

public int compareTo(Object obj)

Returns 1 if this DirectedEdge has a greater angle with the positive x-axis than b", 0 if the DirectedEdges are collinear, and -1 otherwise.

Using the obvious algorithm of simply computing the angle is not robust, since the angle calculation is susceptible to roundoff. A robust algorithm is:

• first compare the quadrants. If the quadrants are different, it it trivial to determine which vector is "greater".
• if the vectors lie in the same quadrant, the robust CGAlgorithms#computeOrientation(Point, Point, Point) function can be used to decide the relative orientation of the vectors.

Specified by:

compareTo in interface Comparable

getAngle

public double getAngle()

Returns the angle that the start of this DirectedEdge makes with the positive x-axis, in radians.

getCoordinate

public Point getCoordinate()

Returns the coordinate of the from-node.

getDirectionPt

public Point getDirectionPt()

Returns a point to which an imaginary line is drawn from the from-node to specify this DirectedEdge's orientation.

getEdge

public Edge getEdge()

Returns this DirectedEdge's parent Edge, or null if it has none.

getEdgeDirection

public boolean getEdgeDirection()

Returns whether the direction of the parent Edge (if any) is the same as that of this Directed Edge.

getFromNode

public Node getFromNode()

Returns the node from which this DirectedEdge leaves.

getQuadrant

public int getQuadrant()

Returns 0, 1, 2, or 3, indicating the quadrant in which this DirectedEdge's orientation lies.

getSym

public DirectedEdge getSym()

Returns the symmetric DirectedEdge -- the other DirectedEdge associated with this DirectedEdge's parent Edge.

getToNode

public Node getToNode()

Returns the node to which this DirectedEdge goes.

isRemoved

public boolean isRemoved()

Tests whether this directed edge has been removed from its containing graph

Specified by:

isRemoved in class GraphComponent

Returns:

true if this directed edge is removed

print

public void print(PrintStream out)

Prints a detailed string representation of this DirectedEdge to the given PrintStream.

setEdge

public void setEdge(Edge parentEdge)

Associates this DirectedEdge with an Edge (possibly null, indicating no associated Edge).

setSym

public void setSym(DirectedEdge sym)

Sets this DirectedEdge's symmetric DirectedEdge, which runs in the opposite direction.