Table of Contents

Class LineIntersector

Namespace
NetTopologySuite.Algorithm
Assembly
NetTopologySuite.dll

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:

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). 

public abstract class LineIntersector
Inheritance
LineIntersector
Derived
Inherited Members

Constructors

LineIntersector()

Creates an instance of this class

protected LineIntersector()

Fields

CollinearIntersection

Indicates that line segments intersect in a line segment

public const int CollinearIntersection = 2

Field Value

int

InputLines

Array of coordinate arrays forming the lines

protected Coordinate[][] InputLines

Field Value

Coordinate[][]

IntersectionLineIndex

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

protected int[] IntersectionLineIndex

Field Value

int[]

IntersectionPoint

Array of

protected Coordinate[] IntersectionPoint

Field Value

Coordinate[]

NoIntersection

Indicates that line segments do not intersect

public const int NoIntersection = 0

Field Value

int

PointIntersection

Indicates that line segments intersect in a single point

public const int PointIntersection = 1

Field Value

int

Result

A value indicating the intersection result

Possible values are: 
protected int Result

Field Value

int

Properties

HasIntersection

Tests whether the input geometries intersect.

public bool HasIntersection { get; }

Property Value

bool

true if the input geometries intersect.

IntersectionNum

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

public int IntersectionNum { get; }

Property Value

int

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

IsCollinear

Gets a value indicating if the computed intersection is collinear

protected bool IsCollinear { get; }

Property Value

bool

IsEndPoint

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

protected bool IsEndPoint { get; }

Property Value

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).

public bool IsProper { get; protected set; }

Property Value

bool

true if the intersection is proper.

Pa

Alias the IntersectionPoint[0] for ease of reference

protected Coordinate Pa { get; }

Property Value

Coordinate

Pb

Alias the IntersectionPoint[1] for ease of reference

protected Coordinate Pb { get; }

Property Value

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.

public PrecisionModel PrecisionModel { get; set; }

Property Value

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.

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

Parameters

p Coordinate
p0 Coordinate
p1 Coordinate

Returns

double

ComputeIntLineIndex()

Computes the IntersectionLineIndex values.

protected void ComputeIntLineIndex()

ComputeIntLineIndex(int)

Computes the intersection line index

protected void ComputeIntLineIndex(int segmentIndex)

Parameters

segmentIndex int

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.

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

Parameters

p1 Coordinate

The 1st point of the 1st segment

p2 Coordinate

The 2nd point of the 1st segment

q1 Coordinate

The 1st point of the 2nd segment

q2 Coordinate

The 2nd point of the 2nd segment

Returns

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.

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

Parameters

p Coordinate
p1 Coordinate
p2 Coordinate

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).

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

Parameters

p1 Coordinate

The 1st point of the 1st segment

p2 Coordinate

The 2nd point of the 1st segment

p3 Coordinate

The 1st point of the 2nd segment

p4 Coordinate

The 2nd point of the 2nd segment

GetEdgeDistance(int, int)

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

public double GetEdgeDistance(int segmentIndex, int intIndex)

Parameters

segmentIndex int

is 0 or 1.

intIndex int

is 0 or 1.

Returns

double

The edge distance of the intersection point.

GetEndpoint(int, int)

Gets an endpoint of an input segment.

public Coordinate GetEndpoint(int segmentIndex, int ptIndex)

Parameters

segmentIndex int

the index of the input segment (0 or 1)

ptIndex int

the index of the endpoint (0 or 1)

Returns

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.

public int GetIndexAlongSegment(int segmentIndex, int intIndex)

Parameters

segmentIndex int

is 0 or 1.

intIndex int

is 0 or 1.

Returns

int

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

GetIntersection(int)

Returns the intIndex'th intersection point.

public Coordinate GetIntersection(int intIndex)

Parameters

intIndex int

is 0 or 1.

Returns

Coordinate

The intIndex'th intersection point.

GetIntersectionAlongSegment(int, int)

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

public Coordinate GetIntersectionAlongSegment(int segmentIndex, int intIndex)

Parameters

segmentIndex int

is 0 or 1.

intIndex int

is 0 or 1.

Returns

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.

public bool IsInteriorIntersection()

Returns

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.

public bool IsInteriorIntersection(int inputLineIndex)

Parameters

inputLineIndex int

Returns

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.

public bool IsIntersection(Coordinate pt)

Parameters

pt Coordinate

Returns

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.

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

Parameters

p Coordinate
p1 Coordinate
p2 Coordinate

Returns

double

ToString() 

public override string ToString()

Returns

string