BufferParameters.java
/*
* Copyright (c) 2016 Vivid Solutions.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
* and the Eclipse Distribution License is available at
*
* http://www.eclipse.org/org/documents/edl-v10.php.
*/
package org.locationtech.jts.operation.buffer;
import org.locationtech.jts.algorithm.Angle;
/**
* A value class containing the parameters which
* specify how a buffer should be constructed.
* <p>
* The parameters allow control over:
* <ul>
* <li>Quadrant segments (accuracy of approximation for circular arcs)
* <li>End Cap style
* <li>Join style
* <li>Mitre limit
* <li>whether the buffer is single-sided
* </ul>
*
* @author Martin Davis
*
*/
public class BufferParameters
{
/**
* Specifies a round line buffer end cap style.
*/
public static final int CAP_ROUND = 1;
/**
* Specifies a flat line buffer end cap style.
*/
public static final int CAP_FLAT = 2;
/**
* Specifies a square line buffer end cap style.
*/
public static final int CAP_SQUARE = 3;
/**
* Specifies a round join style.
*/
public static final int JOIN_ROUND = 1;
/**
* Specifies a mitre join style.
*/
public static final int JOIN_MITRE = 2;
/**
* Specifies a bevel join style.
*/
public static final int JOIN_BEVEL = 3;
/**
* The default number of facets into which to divide a fillet of 90 degrees.
* A value of 8 gives less than 2% max error in the buffer distance.
* For a max error of < 1%, use QS = 12.
* For a max error of < 0.1%, use QS = 18.
*/
public static final int DEFAULT_QUADRANT_SEGMENTS = 8;
/**
* The default mitre limit
* Allows fairly pointy mitres.
*/
public static final double DEFAULT_MITRE_LIMIT = 5.0;
/**
* The default simplify factor
* Provides an accuracy of about 1%, which matches the accuracy of the default Quadrant Segments parameter.
*/
public static final double DEFAULT_SIMPLIFY_FACTOR = 0.01;
private int quadrantSegments = DEFAULT_QUADRANT_SEGMENTS;
private int endCapStyle = CAP_ROUND;
private int joinStyle = JOIN_ROUND;
private double mitreLimit = DEFAULT_MITRE_LIMIT;
private boolean isSingleSided = false;
private double simplifyFactor = DEFAULT_SIMPLIFY_FACTOR;
/**
* Creates a default set of parameters
*
*/
public BufferParameters() {
}
/**
* Creates a set of parameters with the
* given quadrantSegments value.
*
* @param quadrantSegments the number of quadrant segments to use
*/
public BufferParameters(int quadrantSegments)
{
setQuadrantSegments(quadrantSegments);
}
/**
* Creates a set of parameters with the
* given quadrantSegments and endCapStyle values.
*
* @param quadrantSegments the number of quadrant segments to use
* @param endCapStyle the end cap style to use
*/
public BufferParameters(int quadrantSegments,
int endCapStyle)
{
setQuadrantSegments(quadrantSegments);
setEndCapStyle(endCapStyle);
}
/**
* Creates a set of parameters with the
* given parameter values.
*
* @param quadrantSegments the number of quadrant segments to use
* @param endCapStyle the end cap style to use
* @param joinStyle the join style to use
* @param mitreLimit the mitre limit to use
*/
public BufferParameters(int quadrantSegments,
int endCapStyle,
int joinStyle,
double mitreLimit)
{
setQuadrantSegments(quadrantSegments);
setEndCapStyle(endCapStyle);
setJoinStyle(joinStyle);
setMitreLimit(mitreLimit);
}
/**
* Gets the number of quadrant segments which will be used
* to approximate angle fillets in round endcaps and joins.
*
* @return the number of quadrant segments
*/
public int getQuadrantSegments()
{
return quadrantSegments;
}
/**
* Sets the number of line segments in a quarter-circle
* used to approximate angle fillets in round endcaps and joins.
* The value should be at least 1.
* <p>
* This determines the
* error in the approximation to the true buffer curve.
* The default value of 8 gives less than 2% error in the buffer distance.
* For a error of < 1%, use QS = 12.
* For a error of < 0.1%, use QS = 18.
* The error is always less than the buffer distance
* (in other words, the computed buffer curve is always inside the true
* curve).
*
* @param quadSegs the number of segments in a fillet for a circle quadrant
*/
public void setQuadrantSegments(int quadSegs)
{
quadrantSegments = quadSegs;
}
/**
* Computes the maximum distance error due to a given level
* of approximation to a true arc.
*
* @param quadSegs the number of segments used to approximate a quarter-circle
* @return the error of approximation
*/
public static double bufferDistanceError(int quadSegs)
{
double alpha = Angle.PI_OVER_2 / quadSegs;
return 1 - Math.cos(alpha / 2.0);
}
/**
* Gets the end cap style.
*
* @return the end cap style code
*/
public int getEndCapStyle()
{
return endCapStyle;
}
/**
* Specifies the end cap style of the generated buffer.
* The styles supported are {@link #CAP_ROUND}, {@link #CAP_FLAT}, and {@link #CAP_SQUARE}.
* The default is {@link #CAP_ROUND}.
*
* @param endCapStyle the code for the end cap style
*/
public void setEndCapStyle(int endCapStyle)
{
this.endCapStyle = endCapStyle;
}
/**
* Gets the join style.
*
* @return the join style code
*/
public int getJoinStyle()
{
return joinStyle;
}
/**
* Sets the join style for outside (reflex) corners between line segments.
* The styles supported are {@link #JOIN_ROUND},
* {@link #JOIN_MITRE} and {link JOIN_BEVEL}.
* The default is {@link #JOIN_ROUND}.
*
* @param joinStyle the code for the join style
*/
public void setJoinStyle(int joinStyle)
{
this.joinStyle = joinStyle;
}
/**
* Gets the mitre ratio limit.
*
* @return the limit value
*/
public double getMitreLimit()
{
return mitreLimit;
}
/**
* Sets the limit on the mitre ratio used for very sharp corners.
* The mitre ratio is the ratio of the distance from the corner
* to the end of the mitred offset corner.
* When two line segments meet at a sharp angle,
* a miter join will extend far beyond the original geometry.
* (and in the extreme case will be infinitely far.)
* To prevent unreasonable geometry, the mitre limit
* allows controlling the maximum length of the join corner.
* Corners with a ratio which exceed the limit will be beveled.
*
* @param mitreLimit the mitre ratio limit
*/
public void setMitreLimit(double mitreLimit)
{
this.mitreLimit = mitreLimit;
}
/**
* Sets whether the computed buffer should be single-sided.
* A single-sided buffer is constructed on only one side of each input line.
* <p>
* The side used is determined by the sign of the buffer distance:
* <ul>
* <li>a positive distance indicates the left-hand side
* <li>a negative distance indicates the right-hand side
* </ul>
* The single-sided buffer of point geometries is
* the same as the regular buffer.
* <p>
* The End Cap Style for single-sided buffers is
* always ignored,
* and forced to the equivalent of <tt>CAP_FLAT</tt>.
*
* @param isSingleSided true if a single-sided buffer should be constructed
*/
public void setSingleSided(boolean isSingleSided)
{
this.isSingleSided = isSingleSided;
}
/**
* Tests whether the buffer is to be generated on a single side only.
*
* @return true if the generated buffer is to be single-sided
*/
public boolean isSingleSided() {
return isSingleSided;
}
/**
* Gets the simplify factor.
*
* @return the simplify factor
*/
public double getSimplifyFactor() {
return simplifyFactor;
}
/**
* Sets the factor used to determine the simplify distance tolerance
* for input simplification.
* Simplifying can increase the performance of computing buffers.
* Generally the simplify factor should be greater than 0.
* Values between 0.01 and .1 produce relatively good accuracy for the generate buffer.
* Larger values sacrifice accuracy in return for performance.
*
* @param simplifyFactor a value greater than or equal to zero.
*/
public void setSimplifyFactor(double simplifyFactor)
{
this.simplifyFactor = simplifyFactor < 0 ? 0 : simplifyFactor;
}
public BufferParameters copy() {
BufferParameters bp = new BufferParameters();
bp.quadrantSegments = quadrantSegments;
bp.endCapStyle = endCapStyle;
bp.joinStyle = joinStyle;
bp.mitreLimit = mitreLimit;
return bp;
}
}