Module imagingbook.common

Package imagingbook.common.hough

Class HoughLine

java.lang.Object

imagingbook.common.geometry.line.AlgebraicLine

imagingbook.common.geometry.line.HessianLine

imagingbook.common.hough.HoughLine

All Implemented Interfaces:

Primitive2d, ShapeProducer, Comparable<HoughLine>

public class HoughLine
extends HessianLine
implements Comparable<HoughLine>

This class represents a straight line of the form (x - xRef) * cos(angle) + (y - yRef) * sin(angle) = radius. It is used by the Hough transform (see HoughTransformLines). It inherits from HessianLine which is, in turn, a subclass of AlgebraicLine. It adds an arbitrary reference point (xRef, yRef) and a counter (count) for pixel votes. Instances are immutable. See Sec. 12.2 of [1] for additional details.

[1] W. Burger, M.J. Burge, Digital Image Processing – An Algorithmic Introduction, 3rd ed, Springer (2022).

Version:

2022/08/24

Field Summary

Fields inherited from class imagingbook.common.geometry.line.AlgebraicLine

A, B, C

Constructor Summary

Constructors

Constructor	Description
HoughLine(double angle, double radius, double xRef, double yRef, int count)	Constructor, creates a new HoughLine instance from the specified HessianLine parameters (angle, radius), an arbitrary reference point (xRef, yRef) and count.
HoughLine(AlgebraicLine line)	Convenience constructor, creates a new HoughLine instance from a given AlgebraicLine (or any subclass) instance with the same reference point as the original line and zero count.
HoughLine(AlgebraicLine line, double xRef, double yRef, int count)	Constructor, creates a new HoughLine instance from a given AlgebraicLine (or any subclass) instance.

Method Summary

Modifier and Type	Method	Description
int	compareTo(HoughLine other)	Required by the Comparable interface, used for sorting lines by their point count (in descending order, i.e., strong lines come first).
static HoughLine	from(Pnt2d p1, Pnt2d p2, Pnt2d pRef, int count)
int	getCount()
double	getXref()	Returns the x-coordinate of the reference point.
double	getYref()	Returns the y-coordinate of the reference point.
String	toString()

Methods inherited from class imagingbook.common.geometry.line.HessianLine

from, getAngle, getRadius

Methods inherited from class imagingbook.common.geometry.line.AlgebraicLine

equals, equals, from, from, from, getClosestLinePoint, getDistance, getDistance, getParameters, getShape, getShape, getSignedDistance, getSignedDistance, getSquareError, intersect

Methods inherited from class java.lang.Object

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

Methods inherited from interface imagingbook.common.geometry.shape.ShapeProducer

getShape, getShapes, getShapes

Constructor Details

HoughLine

public HoughLine(double angle,
 double radius,
 double xRef,
 double yRef,
 int count)

Constructor, creates a new HoughLine instance from the specified HessianLine parameters (angle, radius), an arbitrary reference point (xRef, yRef) and count.

Parameters:

angle - the line's normal angle (see HessianLine)

radius - the line's radius (distance to reference point)

xRef - reference point x-coordinate

yRef - reference point y-coordinate

count - pixel votes for this line

HoughLine

public HoughLine(AlgebraicLine line,
 double xRef,
 double yRef,
 int count)

Constructor, creates a new HoughLine instance from a given AlgebraicLine (or any subclass) instance. The line parameters are adjusted to the specified reference point (actually only parameter c is modified, since a change of reference point effects only a shift of the line). The two lines are equivalent, i.e., contain the same points (x,y). Thus the distance from a given point (x,y) is the same from the original line and the new line.

Parameters:

line - an existing line (AlgebraicLine or subclass)

xRef - reference point x-coordinate

yRef - reference point y-coordinate

count - pixel votes for this line

HoughLine

public HoughLine(AlgebraicLine line)

Convenience constructor, creates a new HoughLine instance from a given AlgebraicLine (or any subclass) instance with the same reference point as the original line and zero count.

Parameters:

line - a AlgebraicLine instance

Method Details

from

public static HoughLine from(Pnt2d p1,
 Pnt2d p2,
 Pnt2d pRef,
 int count)

getXref

public double getXref()

Description copied from class: AlgebraicLine

Returns the x-coordinate of the reference point. For a AlgebraicLine, the result is always zero. Inheriting classes (like HoughLine) override this method.

Overrides:

getXref in class AlgebraicLine

Returns:

the x-coordinate reference

getYref

public double getYref()

Description copied from class: AlgebraicLine

Returns the y-coordinate of the reference point. For a AlgebraicLine, the result is always zero. Inheriting classes (like HoughLine) override this method.

Overrides:

getYref in class AlgebraicLine

Returns:

the y-coordinate reference

getCount

public int getCount()

compareTo

public int compareTo(HoughLine other)

Required by the Comparable interface, used for sorting lines by their point count (in descending order, i.e., strong lines come first).

Specified by:

compareTo in interface Comparable<HoughLine>

Parameters:

other - another HoughLine instance.

toString

public String toString()

Overrides:

toString in class HessianLine