Class LineIntersector

A LineIntersector is an algorithm that can both test whether two line segments intersect and compute the intersection point(s) if they do.

There are three possible outcomes when determining whether two line segments intersect:

• NoIntersection - the segments do not intersect
• PointIntersection - the segments intersect in a single point
• CollinearIntersection - the segments are collinear and they intersect in a line segment

For segments which intersect in a single point, the point may be either an endpoint or in the interior of each segment. If the point lies in the interior of both segments, this is termed a proper intersection. The property IsProper test for this situation.

The intersection point(s) may be computed in a precise or non-precise manner. Computing an intersection point precisely involves rounding it via a supplied PrecisionModel.

LineIntersectors do not perform an initial envelope intersection test to determine if the segments are disjoint. This is because this class is likely to be used in a context where envelope overlap is already known to occur (or be likely).

Inheritance

object

LineIntersector

RobustLineIntersector

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

Namespace: NetTopologySuite.Algorithm

Assembly: NetTopologySuite.dll

Syntax

public abstract class LineIntersector

Constructors

LineIntersector()

Creates an instance of this class

Declaration

protected LineIntersector()

Fields

CollinearIntersection

Indicates that line segments intersect in a line segment

Declaration

public const int CollinearIntersection = 2

Field Value

Type	Description
int

InputLines

Array of coordinate arrays forming the lines

Declaration

protected Coordinate[][] InputLines

Field Value

Type	Description
Coordinate[][]

IntersectionLineIndex

The indexes of the endpoints of the intersection lines, in order along the corresponding line

Declaration

protected int[] IntersectionLineIndex

Field Value

Type	Description
int[]

IntersectionPoint

Array of

Declaration

protected Coordinate[] IntersectionPoint

Field Value

Type	Description
Coordinate[]

NoIntersection

Indicates that line segments do not intersect

Declaration

public const int NoIntersection = 0

Field Value

Type	Description
int

PointIntersection

Indicates that line segments intersect in a single point

Declaration

public const int PointIntersection = 1

Field Value

Type	Description
int

Result

A value indicating the intersection result

Possible values are:

• NoIntersection
• PointIntersection
• CollinearIntersection

Declaration

protected int Result

Field Value

Type	Description
int

Properties

HasIntersection

Tests whether the input geometries intersect.

Declaration

public bool HasIntersection { get; }

Property Value

Type	Description
bool	true if the input geometries intersect.

IntersectionNum

Returns the number of intersection points found. This will be either 0, 1 or 2.

Declaration

public int IntersectionNum { get; }

Property Value

Type	Description
int	The number of intersection points found (0, 1, or 2)

IsCollinear

Gets a value indicating if the computed intersection is collinear

Declaration

protected bool IsCollinear { get; }

Property Value

Type	Description
bool

IsEndPoint

Gets a value indicating if the intersection is an end-point intersection

Declaration

protected bool IsEndPoint { get; }

Property Value

Type	Description
bool

IsProper

Tests whether an intersection is proper. The intersection between two line segments is considered proper if they intersect in a single point in the interior of both segments (e.g. the intersection is a single point and is not equal to any of the endpoints). The intersection between a point and a line segment is considered proper if the point lies in the interior of the segment (e.g. is not equal to either of the endpoints).

Declaration

public bool IsProper { get; protected set; }

Property Value

Type	Description
bool	true if the intersection is proper.

Pa

Alias the IntersectionPoint[0] for ease of reference

Declaration

protected Coordinate Pa { get; }

Property Value

Type	Description
Coordinate

Pb

Alias the IntersectionPoint[1] for ease of reference

Declaration

protected Coordinate Pb { get; }

Property Value

Type	Description
Coordinate

PrecisionModel

Force computed intersection to be rounded to a given precision model. No getter is provided, because the precision model is not required to be specified.

Declaration

public PrecisionModel PrecisionModel { get; set; }

Property Value

Type	Description
PrecisionModel

Methods

ComputeEdgeDistance(Coordinate, Coordinate, Coordinate)

Computes the "edge distance" of an intersection point p along a segment. The edge distance is a metric of the point along the edge. The metric used is a robust and easy to compute metric function. It is not equivalent to the usual Euclidean metric. It relies on the fact that either the x or the y ordinates of the points in the edge are unique, depending on whether the edge is longer in the horizontal or vertical direction. NOTE: This function may produce incorrect distances for inputs where p is not precisely on p1-p2 (E.g. p = (139,9) p1 = (139,10), p2 = (280,1) produces distance 0.0, which is incorrect. My hypothesis is that the function is safe to use for points which are the result of rounding points which lie on the line, but not safe to use for truncated points.

Declaration

public static double ComputeEdgeDistance(Coordinate p, Coordinate p0, Coordinate p1)

Parameters

Type	Name	Description
Coordinate	p
Coordinate	p0
Coordinate	p1

Returns

Type	Description
double

ComputeIntLineIndex()

Computes the IntersectionLineIndex values.

Declaration

protected void ComputeIntLineIndex()

ComputeIntLineIndex(int)

Computes the intersection line index

Declaration

protected void ComputeIntLineIndex(int segmentIndex)

Parameters

Type	Name	Description
int	segmentIndex	The segment index

ComputeIntersect(Coordinate, Coordinate, Coordinate, Coordinate)

Computes the intersection of two line segments, one defined by p1 and p2, the other by q1 and q2.

Declaration

public abstract int ComputeIntersect(Coordinate p1, Coordinate p2, Coordinate q1, Coordinate q2)

Parameters

Type	Name	Description
Coordinate	p1	The 1st point of the 1st segment
Coordinate	p2	The 2nd point of the 1st segment
Coordinate	q1	The 1st point of the 2nd segment
Coordinate	q2	The 2nd point of the 2nd segment

Returns

Type	Description
int

Remarks

Don't use this function directly, it is not meant for public use. Please call ComputeIntersection(Coordinate, Coordinate, Coordinate, Coordinate) and test HasIntersection or IsCollinear along with IsProper and IsEndPoint.

ComputeIntersection(Coordinate, Coordinate, Coordinate)

Compute the intersection of a point p and the line p1-p2. This function computes the bool value of the hasIntersection test. The actual value of the intersection (if there is one) is equal to the value of p.

Declaration

public abstract void ComputeIntersection(Coordinate p, Coordinate p1, Coordinate p2)

Parameters

Type	Name	Description
Coordinate	p
Coordinate	p1
Coordinate	p2

ComputeIntersection(Coordinate, Coordinate, Coordinate, Coordinate)

Computes the intersection of the lines p1-p2 and p3-p4. This function computes both the bool value of the hasIntersection test and the (approximate) value of the intersection point itself (if there is one).

Declaration

public void ComputeIntersection(Coordinate p1, Coordinate p2, Coordinate p3, Coordinate p4)

Parameters

Type	Name	Description
Coordinate	p1	The 1st point of the 1st segment
Coordinate	p2	The 2nd point of the 1st segment
Coordinate	p3	The 1st point of the 2nd segment
Coordinate	p4	The 2nd point of the 2nd segment

GetEdgeDistance(int, int)

Computes the "edge distance" of an intersection point along the specified input line segment.

Declaration

public double GetEdgeDistance(int segmentIndex, int intIndex)

Parameters

Type	Name	Description
int	segmentIndex	is 0 or 1.
int	intIndex	is 0 or 1.

Returns

Type	Description
double	The edge distance of the intersection point.

GetEndpoint(int, int)

Gets an endpoint of an input segment.

Declaration

public Coordinate GetEndpoint(int segmentIndex, int ptIndex)

Parameters

Type	Name	Description
int	segmentIndex	the index of the input segment (0 or 1)
int	ptIndex	the index of the endpoint (0 or 1)

Returns

Type	Description
Coordinate	The specified endpoint

GetIndexAlongSegment(int, int)

Computes the index (order) of the intIndex'th intersection point in the direction of a specified input line segment.

Declaration

public int GetIndexAlongSegment(int segmentIndex, int intIndex)

Parameters

Type	Name	Description
int	segmentIndex	is 0 or 1.
int	intIndex	is 0 or 1.

Returns

Type	Description
int	The index of the intersection point along the segment (0 or 1).

GetIntersection(int)

Returns the intIndex'th intersection point.

Declaration

public Coordinate GetIntersection(int intIndex)

Parameters

Type	Name	Description
int	intIndex	is 0 or 1.

Returns

Type	Description
Coordinate	The intIndex'th intersection point.

GetIntersectionAlongSegment(int, int)

Computes the intIndex'th intersection point in the direction of a specified input line segment.

Declaration

public Coordinate GetIntersectionAlongSegment(int segmentIndex, int intIndex)

Parameters

Type	Name	Description
int	segmentIndex	is 0 or 1.
int	intIndex	is 0 or 1.

Returns

Type	Description
Coordinate	The intIndex'th intersection point in the direction of the specified input line segment.

IsInteriorIntersection()

Tests whether either intersection point is an interior point of one of the input segments.

Declaration

public bool IsInteriorIntersection()

Returns

Type	Description
bool	true if either intersection point is in the interior of one of the input segment.

IsInteriorIntersection(int)

Tests whether either intersection point is an interior point of the specified input segment.

Declaration

public bool IsInteriorIntersection(int inputLineIndex)

Parameters

Type	Name	Description
int	inputLineIndex

Returns

Type	Description
bool	true if either intersection point is in the interior of the input segment.

IsIntersection(Coordinate)

Test whether a point is a intersection point of two line segments. Note that if the intersection is a line segment, this method only tests for equality with the endpoints of the intersection segment. It does not return true if the input point is internal to the intersection segment.

Declaration

public bool IsIntersection(Coordinate pt)

Parameters

Type	Name	Description
Coordinate	pt

Returns

Type	Description
bool	true if the input point is one of the intersection points.

NonRobustComputeEdgeDistance(Coordinate, Coordinate, Coordinate)

This function is non-robust, since it may compute the square of large numbers. Currently not sure how to improve this.

Declaration

public static double NonRobustComputeEdgeDistance(Coordinate p, Coordinate p1, Coordinate p2)

Parameters

Type	Name	Description
Coordinate	p
Coordinate	p1
Coordinate	p2

Returns

Type	Description
double

ToString()

Declaration

public override string ToString()

Returns

Type	Description
string

Overrides

object.ToString()