diva.sketch.toolbox

Class ApproximateStrokeFilter

java.lang.Object

diva.sketch.toolbox.StrokeFilter

diva.sketch.toolbox.ApproximateStrokeFilter

public class ApproximateStrokeFilter
extends StrokeFilter

An object which filters a pen stroke using "approximation by line segments" technique, (Hanaki, Temma, Yoshida, "An On-line Character Recognition Aimed at a Substitution for a Billing Machine Keyboard", Pattern Recognition, Vol.8, pp63-71, 1976).

Version:

$Revision: 1.12 $

Author:

Heloise Hse (hwawen@eecs.berkeley.edu)

Field Summary

Fields

Modifier and Type	Field and Description
static double	DEFAULT_THRESH_DISTANCE If the farthest point from a line segment is less than the DEFAULT_THRESH_DISTANCE, we can throw away all the in-between points, because they are almost colinear.

Fields inherited from class diva.sketch.toolbox.StrokeFilter

PROPERTY_KEY

Constructor Summary

Constructors

Constructor and Description
ApproximateStrokeFilter() Construct a ApproximateStrokeFilter with default threshold distance of 2 units.

Method Summary

Modifier and Type	Method and Description
TimedStroke	apply(TimedStroke s) Reduce the number of points in the given pen stroke using the "approximation by line segments" algorithm.
static TimedStroke	approximate(TimedStroke s) Reduce the number of points in the given pen stroke using the "approximation by line segments" algorithm.
static TimedStroke	approximate(TimedStroke s, double threshDist) Reduce the number of points in the given pen stroke using the "approximation by line segments" algorithm.
void	setThreshDistance(int val) Set the threshold distance of a point from a line segment.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_THRESH_DISTANCE

public static final double DEFAULT_THRESH_DISTANCE

If the farthest point from a line segment is less than the DEFAULT_THRESH_DISTANCE, we can throw away all the in-between points, because they are almost colinear. If the distance is greather than this value, we recursively filter the stroke by breaking off at the farthest point. The default value is set to 2 units.

See Also:

Constant Field Values

Constructor Detail

ApproximateStrokeFilter

public ApproximateStrokeFilter()

Construct a ApproximateStrokeFilter with default threshold distance of 2 units.

Method Detail

apply

public TimedStroke apply(TimedStroke s)

Reduce the number of points in the given pen stroke using the "approximation by line segments" algorithm.

Algorithm: Form a line with the first and last points of the stroke. Find a farthest point (P) from the line segment such that distance between the line and P exceeds a threshold value. Then, break the line segment into 2 and recursively apply filtering on the 2 parts, (first, P) and (P, last). The threshold value is defaulted to DEFAULT_THRESH_DISTANCE.

Specified by:

apply in class StrokeFilter

Parameters:

s - the stroke to be filtered.

approximate

public static TimedStroke approximate(TimedStroke s)

Reduce the number of points in the given pen stroke using the "approximation by line segments" algorithm.

Algorithm: Form a line with the first and last points of the stroke. Find a farthest point (P) from the line segment such that distance between the line and P exceeds a threshold value. Then, break the line segment into 2 and recursively apply filtering on the 2 parts, (first, P) and (P, last). The threshold value is defaulted to DEFAULT_THRESH_DISTANCE.

Parameters:

s - the stroke to be filtered.

approximate

public static TimedStroke approximate(TimedStroke s,
                                      double threshDist)

Reduce the number of points in the given pen stroke using the "approximation by line segments" algorithm.

Algorithm: Form a line with the first and last points of the stroke. Find a farthest point (P) from the line segment such that distance between the line and P exceeds a threshold value (threshDist). Then, break the line segment into 2 and recursively apply filtering on the 2 parts, (first, P) and (P, last).

setThreshDistance

public void setThreshDistance(int val)

Set the threshold distance of a point from a line segment. If 'val' is negative, throws an IllegalArgumentException.