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The JTS Topology Suite is an API for modelling and
manipulating 2-dimensional linear geometry. It provides
numerous geometric predicates and functions. JTS
conforms to the Simple Features Specification for
SQL published by the Open GIS Consortium.
/*
* The JTS Topology Suite is a collection of Java classes that
* implement the fundamental operations required to validate a given
* geo-spatial data set to a known topological specification.
*
* Copyright (C) 2001 Vivid Solutions
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* For more information, contact:
*
* Vivid Solutions
* Suite #1A
* 2328 Government Street
* Victoria BC V8T 5G5
* Canada
*
* (250)385-6040
* www.vividsolutions.com
*/
package com.vividsolutions.jts.operation.buffer;
/**
* Contains the parameters which
* describe how a buffer should be constructed.
*
* @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;
private int quadrantSegments = DEFAULT_QUADRANT_SEGMENTS;
private int endCapStyle = CAP_ROUND;
private int joinStyle = JOIN_ROUND;
private double mitreLimit = DEFAULT_MITRE_LIMIT;
/**
* 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
*
* @return the number of quadrant segments
*/
public int getQuadrantSegments()
{
return quadrantSegments;
}
/**
* Sets the number of line segments used to approximate an angle fillet.
*
* - If quadSegs >= 1, joins are round, and quadSegs indicates the number of
* segments to use to approximate a quarter-circle.
*
- If quadSegs = 0, joins are bevelled (flat)
*
- If quadSegs < 0, joins are mitred, and the value of qs
* indicates the mitre ration limit as
*
* mitreLimit = |quadSegs|
*
*
* For round joins, quadSegs determines the maximum
* error in the approximation to the true buffer curve.
* The default 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.
* The error is always less than the buffer distance
* (in other words, the computed buffer curve is always inside the true
* curve).
*
* @param quadrantSegments the number of segments in a fillet for a quadrant
*/
public void setQuadrantSegments(int quadSegs)
{
quadrantSegments = quadSegs;
/**
* Indicates how to construct fillets.
* If qs >= 1, fillet is round, and qs indicates number of
* segments to use to approximate a quarter-circle.
* If qs = 0, fillet is bevelled flat (i.e. no filleting is performed)
* If qs < 0, fillet is mitred, and absolute value of qs
* indicates maximum length of mitre according to
*
* mitreLimit = |qs|
*/
if (quadrantSegments == 0)
joinStyle = JOIN_BEVEL;
if (quadrantSegments < 0) {
joinStyle = JOIN_MITRE;
mitreLimit = Math.abs(quadrantSegments);
}
if (quadSegs <= 0) {
quadrantSegments = 1;
}
/**
* If join style was set by the quadSegs value,
* use the default for the actual quadrantSegments value.
*/
if (joinStyle != JOIN_ROUND) {
quadrantSegments = DEFAULT_QUADRANT_SEGMENTS;
}
}
/**
* 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 = Math.PI / 2.0 / quadSegs;
return 1 - Math.cos(alpha / 2.0);
}
/**
* Gets the end cap style.
*
* @return the end cap style
*/
public int getEndCapStyle()
{
return endCapStyle;
}
/**
* Specifies the end cap style of the generated buffer.
* The styles supported are {@link #CAP_ROUND}, {@link #CAP_BUTT}, and {@link #CAP_SQUARE}.
* The default is CAP_ROUND.
*
* @param endCapStyle the end cap style to specify
*/
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.
* Allowable values are {@link JOIN_ROUND} (which is the default),
* {@link JOIN_MITRE} and {link JOIN_BEVEL}.
*
* @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;
}
}
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