Class OverlayNG

Computes the geometric overlay of two Geometrys, using an explicit precision model to allow robust computation.

The overlay can be used to determine any of the following set-theoretic operations (boolean combinations) of the geometries:

Intersectionall points which lie in both geometries
Unionall points which lie in at least one geometry
Differenceall points which lie in the first geometry but not the second
SymDifferenceall points which lie in one geometry but not both

Input geometries may have different dimension. Input collections must be homogeneous (all elements must have the same dimension). Inputs may be simple GeometryCollections. A GeometryCollection is simple if it can be flattened into a valid Multi-geometry; i.e.it is homogeneous and does not contain any overlapping Polygons.

The precision model used for the computation can be supplied independent of the precision model of the input geometry. The main use for this is to allow using a fixed precision for geometry with a floating precision model. This does two things: ensures robust computation; and forces the output to be validly rounded to the precision model.

For fixed precision models noding is performed using a SnapRoundingNoder. This provides robust computation(as long as precision is limited to around 13 decimal digits).

For floating precision an MCIndexNoder is used. This is not fully robust, so can sometimes result in TopologyExceptions being thrown. For robust full-precision overlay see OverlayNGRobust.

A custom INoder can be supplied. This allows using a more performant noding strategy in specific cases, for instance in CoverageUnion.

Note: If a SnappingNoder is used it is best to specify a fairly small snap tolerance, since the intersection clipping optimization can interact with the snapping to alter the result.

Optionally the overlay computation can process using strict mode (via StrictMode = true). In strict mode result semantics are:

Lines and Points resulting from topology collapses are not included in the result
Result geometry is homogeneous for the Intersection and Difference operations.
Result geometry is homogeneous for the Union and SymDifference operations if the inputs have the same dimension

Strict mode has the following benefits:

Results are simpler
Overlay operations are easily chainable without needing to remove lower-dimension elements

The original JTS overlay semantics corresponds to non-strict mode.

If a robustness error occurs, a TopologyException is thrown. These are usually caused by numerical rounding causing the noding output to not be fully noded. For robust computation with full-precision OverlayNGRobust can be used.

Inheritance

object

OverlayNG

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: NetTopologySuite.Operation.OverlayNG

Assembly: NetTopologySuite.dll

Syntax

public sealed class OverlayNG

Constructors

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OverlayNG(Geometry, Geometry, PrecisionModel, ElevationModel, SpatialFunction)

Creates an overlay operation on the given geometries, with a defined precision model.

Declaration

public OverlayNG(Geometry geom0, Geometry geom1, PrecisionModel pm, ElevationModel em, SpatialFunction opCode)

Parameters

Type	Name	Description
Geometry	geom0	The A operand geometry
Geometry	geom1	The B operand geometry (may be `null`)
PrecisionModel	pm	The precision model to use
ElevationModel	em	The elevation model to use. May be `null`
SpatialFunction	opCode	The overlay opcode

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OverlayNG(Geometry, Geometry, PrecisionModel, SpatialFunction)

Creates an overlay operation on the given geometries, with a defined precision model.

Declaration

public OverlayNG(Geometry geom0, Geometry geom1, PrecisionModel pm, SpatialFunction opCode)

Parameters

Type	Name	Description
Geometry	geom0	The A operand geometry
Geometry	geom1	The B operand geometry (may be `null`)
PrecisionModel	pm	The precision model to use
SpatialFunction	opCode	The overlay opcode

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OverlayNG(Geometry, Geometry, SpatialFunction)

Creates an overlay operation on the given geometries using the precision model of the geometries.

The noder is chosen according to the precision model specified.

For Fixed a snap - rounding noder is used, and the computation is robust.
For Floating a non - snapping noder is used, and this computation may not be robust.

Declaration

public OverlayNG(Geometry geom0, Geometry geom1, SpatialFunction opCode)

Parameters

Type	Name	Description
Geometry	geom0	The A operand geometry
Geometry	geom1	The B operand geometry (may be `null`)
SpatialFunction	opCode	The overlay opcode

Fields

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DIFFERENCE

The code for the Difference overlay operation.

Declaration

public const SpatialFunction DIFFERENCE = Difference

Field Value

Type	Description
SpatialFunction

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INTERSECTION

The code for the Intersection overlay operation.

Declaration

public const SpatialFunction INTERSECTION = Intersection

Field Value

Type	Description
SpatialFunction

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SYMDIFFERENCE

The code for the Symmetric Difference overlay operation.

Declaration

public const SpatialFunction SYMDIFFERENCE = SymDifference

Field Value

Type	Description
SpatialFunction

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UNION

The code for the Union overlay operation.

Declaration

public const SpatialFunction UNION = Union

Field Value

Type	Description
SpatialFunction

Properties

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AreaResultOnly

Gets or sets whether the result can contain only Polygon components. This is used if it is known that the result must be an (possibly empty) area.

Declaration

public bool AreaResultOnly { get; set; }

Property Value

Type	Description
bool	`true` if the result should contain only area components

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Noder

Declaration

public INoder Noder { get; set; }

Property Value

Type	Description
INoder

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Optimized

Gets or sets a value indicating whether overlay processing optimizations are enabled.

It may be useful to disable optimizations for testing purposes.

Default is true (optimization enabled).

Declaration

public bool Optimized { get; set; }

Property Value

Type	Description
bool

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OutputEdges

Declaration

public bool OutputEdges { get; set; }

Property Value

Type	Description
bool

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OutputNodedEdges

Declaration

public bool OutputNodedEdges { get; set; }

Property Value

Type	Description
bool

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OutputResultEdges

Declaration

public bool OutputResultEdges { get; set; }

Property Value

Type	Description
bool

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StrictMode

Gets or sets whether the overlay results are computed according to strict mode semantics.

Lines resulting from topology collapse are not included
Result geometry is homogeneous for the Intersection and Difference operations.
Result geometry is homogeneous for the Union and SymDifference operations if the inputs have the same dimension

Declaration

public bool StrictMode { get; set; }

Property Value

Type	Description
bool

Methods

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GetResult()

Gets the result of the overlay operation. e

Declaration

public Geometry GetResult()

Returns

Type	Description
Geometry	The result of the overlay operation.

Exceptions

Type	Condition
ArgumentException	Thrown, if the input is not supported (e.g. a mixed-dimension geometry)
TopologyException	Thrown, if a robustness error occurs

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Overlay(Geometry, Geometry, SpatialFunction)

Computes an overlay operation on the given geometry operands, using the precision model of the geometry. and an appropriate noder.

The noder is chosen according to the precision model specified.

For Fixed a snap-rounding noder is used, and the computation is robust.
For Floating a non-snapping noder is used, and this computation may not be robust. If errors occur a TopologyException is thrown.

Declaration

public static Geometry Overlay(Geometry geom0, Geometry geom1, SpatialFunction opCode)

Parameters

Type	Name	Description
Geometry	geom0	The first geometry argument
Geometry	geom1	The second geometry argument
SpatialFunction	opCode	The code for the desired overlay operation

Returns

Type	Description
Geometry	The result of the overlay operation

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Overlay(Geometry, Geometry, SpatialFunction, PrecisionModel)

Computes an overlay operation for the given geometry operands, with the noding strategy determined by the precision model.

Declaration

public static Geometry Overlay(Geometry geom0, Geometry geom1, SpatialFunction opCode, PrecisionModel pm)

Parameters

Type	Name	Description
Geometry	geom0	The first geometry argument
Geometry	geom1	The second geometry argument
SpatialFunction	opCode	The code for the desired overlay operation
PrecisionModel	pm	The precision model to use

Returns

Type	Description
Geometry	The result of the overlay operation

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Overlay(Geometry, Geometry, SpatialFunction, PrecisionModel, INoder)

Computes an overlay operation for the given geometry operands, using a supplied INoder.

Declaration

public static Geometry Overlay(Geometry geom0, Geometry geom1, SpatialFunction opCode, PrecisionModel pm, INoder noder)

Parameters

Type	Name	Description
Geometry	geom0	The first geometry argument
Geometry	geom1	The second geometry argument
SpatialFunction	opCode	The code for the desired overlay operation
PrecisionModel	pm	The precision model to use (which may be null if the noder does not use one)
INoder	noder	The noder to use

Returns

Type	Description
Geometry	The result of the overlay operation

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Overlay(Geometry, Geometry, SpatialFunction, INoder)

Computes an overlay operation on the given geometry operands, using a supplied INoder.

Declaration

public static Geometry Overlay(Geometry geom0, Geometry geom1, SpatialFunction opCode, INoder noder)

Parameters

Type	Name	Description
Geometry	geom0	The first geometry argument
Geometry	geom1	The second geometry argument
SpatialFunction	opCode	The code for the desired overlay operation
INoder	noder	The noder to use

Returns

Type	Description
Geometry	The result of the overlay operation