org.apache.commons.math3.geometry.euclidean.twod

## Class Line

- java.lang.Object
- - org.apache.commons.math3.geometry.euclidean.twod.Line

All Implemented Interfaces:
  Embedding<Euclidean2D,Euclidean1D>, Hyperplane<Euclidean2D>

    public class Line
    extends Object
    implements Hyperplane<Euclidean2D>, Embedding<Euclidean2D,Euclidean1D>

This class represents an oriented line in the 2D plane.

An oriented line can be defined either by prolongating a line segment between two points past these points, or by one point and an angular direction (in trigonometric orientation).

Since it is oriented the two half planes at its two sides are unambiguously identified as a left half plane and a right half plane. This can be used to identify the interior and the exterior in a simple way by local properties only when part of a line is used to define part of a polygon boundary.

A line can also be used to completely define a reference frame in the plane. It is sufficient to select one specific point in the line (the orthogonal projection of the original reference frame on the line) and to use the unit vector in the line direction and the orthogonal vector oriented from left half plane to right half plane. We define two coordinates by the process, the abscissa along the line, and the offset across the line. All points of the plane are uniquely identified by these two coordinates. The line is the set of points at zero offset, the left half plane is the set of points with negative offsets and the right half plane is the set of points with positive offsets.

Since:
  3.0
Version:
  $Id: Line.java 1422195 2012-12-15 06:45:18Z psteitz $

### Nested Class Summary

Nested Classes
`private static class` `Line.LineTransform` Class embedding an affine transform.

### Field Summary

Fields
`private double` `angle` Angle with respect to the abscissa axis.
`private double` `cos` Cosine of the line angle.
`private double` `originOffset` Offset of the frame origin.
`private double` `sin` Sine of the line angle.

### Constructor Summary

Constructors
`private` `Line(double angle, double cos, double sin, double originOffset)` Build a line from its internal characteristics.
`` `Line(Line line)` Copy constructor.
`` `Line(Vector2D p, double angle)` Build a line from a point and an angle.
`` `Line(Vector2D p1, Vector2D p2)` Build a line from two points.

### Method Summary

Methods
`boolean` `contains(Vector2D p)` Check if the line contains a point.
`Line` `copySelf()` Copy the instance.
`double` `distance(Vector2D p)` Compute the distance between the instance and a point.
`double` `getAngle()` Get the angle of the line.
`double` `getOffset(Line line)` Get the offset (oriented distance) of a parallel line.
`double` `getOffset(Vector<Euclidean2D> point)` Get the offset (oriented distance) of a point.
`double` `getOriginOffset()` Get the offset of the origin.
`Vector2D` `getPointAt(Vector1D abscissa, double offset)` Get one point from the plane.
`Line` `getReverse()` Get the reverse of the instance.
`static Transform<Euclidean2D,Euclidean1D>` `getTransform(AffineTransform transform)` Get a `Transform` embedding an affine transform.
`Vector2D` `intersection(Line other)` Get the intersection point of the instance and another line.
`boolean` `isParallelTo(Line line)` Check the instance is parallel to another line.
`void` `reset(Vector2D p, double alpha)` Reset the instance as if built from a line and an angle.
`void` `reset(Vector2D p1, Vector2D p2)` Reset the instance as if built from two points.
`void` `revertSelf()` Revert the instance.
`boolean` `sameOrientationAs(Hyperplane<Euclidean2D> other)` Check if the instance has the same orientation as another hyperplane.
`void` `setAngle(double angle)` Set the angle of the line.
`void` `setOriginOffset(double offset)` Set the offset of the origin.
`Vector2D` `toSpace(Vector<Euclidean1D> point)` Transform a sub-space point into a space point.
`Vector1D` `toSubSpace(Vector<Euclidean2D> point)` Transform a space point into a sub-space point.
`void` `translateToPoint(Vector2D p)` Translate the line to force it passing by a point.
`SubLine` `wholeHyperplane()` Build a sub-hyperplane covering the whole hyperplane.
`PolygonsSet` `wholeSpace()` Build a region covering the whole space.

### Methods inherited from class java.lang.Object

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

### Field Detail

#### angle

    private double angle

Angle with respect to the abscissa axis.

#### cos

    private double cos

Cosine of the line angle.

#### sin

    private double sin

Sine of the line angle.

#### originOffset

    private double originOffset

Offset of the frame origin.

### Constructor Detail

#### Line

    public Line(Vector2D p1,
        Vector2D p2)

Build a line from two points.

The line is oriented from p1 to p2

Parameters:
  `p1` - first point
  `p2` - second point

#### Line

    public Line(Vector2D p,
        double angle)

Build a line from a point and an angle.

Parameters:
  `p` - point belonging to the line
  `angle` - angle of the line with respect to abscissa axis

#### Line

    private Line(double angle,
        double cos,
        double sin,
        double originOffset)

Build a line from its internal characteristics.

Parameters:
  `angle` - angle of the line with respect to abscissa axis
  `cos` - cosine of the angle
  `sin` - sine of the angle
  `originOffset` - offset of the origin

#### Line

    public Line(Line line)

Copy constructor.

The created instance is completely independent from the original instance, it is a deep copy.

Parameters:
  `line` - line to copy

### Method Detail

#### copySelf

    public Line copySelf()

Copy the instance.

The instance created is completely independant of the original one. A deep copy is used, none of the underlying objects are shared (except for immutable objects).

Specified by:
  `copySelf` in interface `Hyperplane<Euclidean2D>`
Returns:
  a new hyperplane, copy of the instance

#### reset

    public void reset(Vector2D p1,
             Vector2D p2)

Reset the instance as if built from two points.

The line is oriented from p1 to p2

Parameters:
  `p1` - first point
  `p2` - second point

#### reset

    public void reset(Vector2D p,
             double alpha)

Reset the instance as if built from a line and an angle.

Parameters:
  `p` - point belonging to the line
  `alpha` - angle of the line with respect to abscissa axis

#### revertSelf

    public void revertSelf()

Revert the instance.

#### getReverse

    public Line getReverse()

Get the reverse of the instance.

Get a line with reversed orientation with respect to the instance. A new object is built, the instance is untouched.

Returns:
  a new line, with orientation opposite to the instance orientation

#### toSubSpace

    public Vector1D toSubSpace(Vector<Euclidean2D> point)

Transform a space point into a sub-space point.

Specified by:
  `toSubSpace` in interface `Embedding<Euclidean2D,Euclidean1D>`
Parameters:
  `point` - n-dimension point of the space
Returns:
  (n-1)-dimension point of the sub-space corresponding to the specified space point
See Also:
  `Embedding.toSpace(org.apache.commons.math3.geometry.Vector<T>)`

#### toSpace

    public Vector2D toSpace(Vector<Euclidean1D> point)

Transform a sub-space point into a space point.

Specified by:
  `toSpace` in interface `Embedding<Euclidean2D,Euclidean1D>`
Parameters:
  `point` - (n-1)-dimension point of the sub-space
Returns:
  n-dimension point of the space corresponding to the specified sub-space point
See Also:
  `Embedding.toSubSpace(org.apache.commons.math3.geometry.Vector)`

#### intersection

    public Vector2D intersection(Line other)

Get the intersection point of the instance and another line.

Parameters:
  `other` - other line
Returns:
  intersection point of the instance and the other line or null if there are no intersection points

#### wholeHyperplane

    public SubLine wholeHyperplane()

Build a sub-hyperplane covering the whole hyperplane.

Specified by:
  `wholeHyperplane` in interface `Hyperplane<Euclidean2D>`
Returns:
  a sub-hyperplane covering the whole hyperplane

#### wholeSpace

    public PolygonsSet wholeSpace()

Build a region covering the whole space.

Specified by:
  `wholeSpace` in interface `Hyperplane<Euclidean2D>`
Returns:
  a region containing the instance (really a `PolygonsSet` instance)

#### getOffset

    public double getOffset(Line line)

Get the offset (oriented distance) of a parallel line.

This method should be called only for parallel lines otherwise the result is not meaningful.

The offset is 0 if both lines are the same, it is positive if the line is on the right side of the instance and negative if it is on the left side, according to its natural orientation.

Parameters:
  `line` - line to check
Returns:
  offset of the line

#### getOffset

    public double getOffset(Vector<Euclidean2D> point)

Get the offset (oriented distance) of a point.

The offset is 0 if the point is on the underlying hyperplane, it is positive if the point is on one particular side of the hyperplane, and it is negative if the point is on the other side, according to the hyperplane natural orientation.

Specified by:
  `getOffset` in interface `Hyperplane<Euclidean2D>`
Parameters:
  `point` - point to check
Returns:
  offset of the point

#### sameOrientationAs

    public boolean sameOrientationAs(Hyperplane<Euclidean2D> other)

Check if the instance has the same orientation as another hyperplane.

This method is expected to be called on parallel hyperplanes. The method should not re-check for parallelism, only for orientation, typically by testing something like the sign of the dot-products of normals.

Specified by:
  `sameOrientationAs` in interface `Hyperplane<Euclidean2D>`
Parameters:
  `other` - other hyperplane to check against the instance
Returns:
  true if the instance and the other hyperplane have the same orientation

#### getPointAt

    public Vector2D getPointAt(Vector1D abscissa,
                      double offset)

Get one point from the plane.

Parameters:
  `abscissa` - desired abscissa for the point
  `offset` - desired offset for the point
Returns:
  one point in the plane, with given abscissa and offset relative to the line

#### contains

    public boolean contains(Vector2D p)

Check if the line contains a point.

Parameters:
  `p` - point to check
Returns:
  true if p belongs to the line

#### distance

    public double distance(Vector2D p)

Compute the distance between the instance and a point.

This is a shortcut for invoking FastMath.abs(getOffset(p)), and provides consistency with what is in the org.apache.commons.math3.geometry.euclidean.threed.Line class.

Parameters:
  `p` - to check
Returns:
  distance between the instance and the point
Since:
  3.1

#### isParallelTo

    public boolean isParallelTo(Line line)

Check the instance is parallel to another line.

Parameters:
  `line` - other line to check
Returns:
  true if the instance is parallel to the other line (they can have either the same or opposite orientations)

#### translateToPoint

    public void translateToPoint(Vector2D p)

Translate the line to force it passing by a point.

Parameters:
  `p` - point by which the line should pass

#### getAngle

    public double getAngle()

Get the angle of the line.

Returns:
  the angle of the line with respect to the abscissa axis

#### setAngle

    public void setAngle(double angle)

Set the angle of the line.

Parameters:
  `angle` - new angle of the line with respect to the abscissa axis

#### getOriginOffset

    public double getOriginOffset()

Get the offset of the origin.

Returns:
  the offset of the origin

#### setOriginOffset

    public void setOriginOffset(double offset)

Set the offset of the origin.

Parameters:
  `offset` - offset of the origin

#### getTransform

    public static Transform<Euclidean2D,Euclidean1D> getTransform(AffineTransform transform)
                                                           throws MathIllegalArgumentException

Get a `Transform` embedding an affine transform.

Parameters:
  `transform` - affine transform to embed (must be inversible otherwise the `apply(Hyperplane)` method would work only for some lines, and fail for other ones)
Returns:
  a new transform that can be applied to either `Vector2D`, `Line` or `SubHyperplane` instances
Throws:
  `MathIllegalArgumentException` - if the transform is non invertible