org.locationtech.jts.operation.buffer

Class OffsetCurve

java.lang.Object

org.locationtech.jts.operation.buffer.OffsetCurve

public class OffsetCurve
extends Object

Computes an offset curve from a geometry. An offset curve is a linear geometry which is offset a given distance from the input. If the offset distance is positive the curve lies on the left side of the input; if it is negative the curve is on the right side. The curve(s) have the same direction as the input line(s). The result for a zero offset distance is a copy of the input linework.

The offset curve is based on the boundary of the buffer for the geometry at the offset distance (see BufferOp. The normal mode of operation is to return the sections of the buffer boundary which lie on the raw offset curve (obtained via rawOffset(LineString, double). The offset curve will contain multiple sections if the input self-intersects or has close approaches. The computed sections are ordered along the raw offset curve. Sections are disjoint. They never self-intersect, but may be rings.

• For a LineString the offset curve is a linear geometry (LineString or MultiLineString).
• For a Point or MultiPoint the offset curve is an empty LineString.
• For a Polygon the offset curve is the boundary of the polygon buffer (which may be a MultiLineString.
• For a collection the output is a MultiLineString containing the offset curves of the elements.

In "joined" mode (see setJoined(boolean) the sections computed for each input line are joined into a single offset curve line. The joined curve may self-intersect. At larger offset distances the curve may contain "flat-line" artifacts in places where the input self-intersects.

Offset curves support setting the number of quadrant segments, the join style, and the mitre limit (if applicable) via the BufferParameters.

Author:

Martin Davis

Constructor Summary

Constructors

Constructor and Description
OffsetCurve(Geometry geom, double distance) Creates a new instance for computing an offset curve for a geometry at a given distance.
OffsetCurve(Geometry geom, double distance, BufferParameters bufParams) Creates a new instance for computing an offset curve for a geometry at a given distance.

Method Summary

Modifier and Type	Method and Description
Geometry	getCurve() Gets the computed offset curve lines.
static Geometry	getCurve(Geometry geom, double distance) Computes the offset curve of a geometry at a given distance.
static Geometry	getCurve(Geometry geom, double distance, int quadSegs, int joinStyle, double mitreLimit) Computes the offset curve of a geometry at a given distance, with specified quadrant segments, join style and mitre limit.
static Geometry	getCurveJoined(Geometry geom, double distance) Computes the offset curve of a geometry at a given distance, joining curve sections into a single line for each input line.
static Coordinate[]	rawOffset(LineString line, double distance) Gets the raw offset curve for a line at a given distance, with default buffer parameters.
static Coordinate[]	rawOffset(LineString line, double distance, BufferParameters bufParams) Gets the raw offset curve for a line at a given distance.
void	setJoined(boolean isJoined) Computes a single curve line for each input linear component, by joining curve sections in order along the raw offset curve.

Methods inherited from class java.lang.Object

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

Constructor Detail

OffsetCurve

public OffsetCurve(Geometry geom,
                   double distance)

Creates a new instance for computing an offset curve for a geometry at a given distance. with default quadrant segments (BufferParameters.DEFAULT_QUADRANT_SEGMENTS) and join style (BufferParameters#JOIN_STYLE).

Parameters:

geom - the geometry to offset

distance - the offset distance (positive for left, negative for right)

See Also:

BufferParameters

OffsetCurve

public OffsetCurve(Geometry geom,
                   double distance,
                   BufferParameters bufParams)

Creates a new instance for computing an offset curve for a geometry at a given distance. setting the quadrant segments and join style and mitre limit via BufferParameters.

Parameters:

geom - the geometry to offset

distance - the offset distance (positive for left, negative for right)

bufParams - the buffer parameters to use

Method Detail

getCurve

public static Geometry getCurve(Geometry geom,
                                double distance)

Computes the offset curve of a geometry at a given distance.

Parameters:

geom - a geometry

distance - the offset distance (positive for left, negative for right)

Returns:

the offset curve

getCurve

public static Geometry getCurve(Geometry geom,
                                double distance,
                                int quadSegs,
                                int joinStyle,
                                double mitreLimit)

Computes the offset curve of a geometry at a given distance, with specified quadrant segments, join style and mitre limit.

Parameters:

geom - a geometry

distance - the offset distance (positive for left, negative for right)

quadSegs - the quadrant segments (-1 for default)

joinStyle - the join style (-1 for default)

mitreLimit - the mitre limit (-1 for default)

Returns:

the offset curve

getCurveJoined

public static Geometry getCurveJoined(Geometry geom,
                                      double distance)

Computes the offset curve of a geometry at a given distance, joining curve sections into a single line for each input line.

Parameters:

geom - a geometry

distance - the offset distance (positive for left, negative for right)

Returns:

the joined offset curve

setJoined

public void setJoined(boolean isJoined)

Computes a single curve line for each input linear component, by joining curve sections in order along the raw offset curve. The default mode is to compute separate curve sections.

Parameters:

isJoined - true if joined mode should be used.

getCurve

public Geometry getCurve()

Gets the computed offset curve lines.

Returns:

the offset curve geometry

rawOffset

public static Coordinate[] rawOffset(LineString line,
                                     double distance,
                                     BufferParameters bufParams)

Gets the raw offset curve for a line at a given distance. The quadrant segments, join style and mitre limit can be specified via BufferParameters.

The raw offset line may contain loops and other artifacts which are not present in the true offset curve.

Parameters:

line - the line to offset

distance - the offset distance (positive for left, negative for right)

bufParams - the buffer parameters to use

Returns:

the raw offset curve points

rawOffset

public static Coordinate[] rawOffset(LineString line,
                                     double distance)

Gets the raw offset curve for a line at a given distance, with default buffer parameters.

Parameters:

line - the line to offset

distance - the offset distance (positive for left, negative for right)

Returns:

the raw offset curve points