Class OverlayNG

java.lang.Object
org.locationtech.jts.operation.overlayng.OverlayNG
public class OverlayNG extends Object
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:

  • INTERSECTION - all points which lie in both geometries
  • UNION - all points which lie in at least one geometry
  • DIFFERENCE - all points which lie in the first geometry but not the second
  • SYMDIFFERENCE - all 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
invalid reference 
GeometryCollection
s. 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 Noder can be supplied. This allows using a more performant noding strategy in specific cases, for instance in CoverageUnion.

Note:invalid input: '<'/b 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 setStrictMode(boolean). 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 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.

Author:
mdavis
See Also:

  • Field Details

    • INTERSECTION

      public static final int INTERSECTION
      The code for the Intersection overlay operation.
      See Also:

    • UNION

      public static final int UNION
      The code for the Union overlay operation.
      See Also:

    • DIFFERENCE

      public static final int DIFFERENCE
      The code for the Difference overlay operation.
      See Also:

    • SYMDIFFERENCE

      public static final int SYMDIFFERENCE
      The code for the Symmetric Difference overlay operation.
      See Also:

  • Constructor Details

    • OverlayNG

      public OverlayNG(Geometry geom0, Geometry geom1, PrecisionModel pm, int opCode)
      Creates an overlay operation on the given geometries, with a defined precision model. The noding strategy is determined by the precision model.
      Parameters:
      geom0 - the A operand geometry
      geom1 - the B operand geometry (may be null)
      pm - the precision model to use
      opCode - the overlay opcode

    • OverlayNG

      public OverlayNG(Geometry geom0, Geometry geom1, int opCode)
      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.

      Parameters:
      geom0 - the A operand geometry
      geom1 - the B operand geometry (may be null)
      opCode - the overlay opcode

  • Method Details

    • overlay

      public static Geometry overlay(Geometry geom0, Geometry geom1, int opCode, PrecisionModel pm)
      Computes an overlay operation for the given geometry operands, with the noding strategy determined by the precision model.
      Parameters:
      geom0 - the first geometry argument
      geom1 - the second geometry argument
      opCode - the code for the desired overlay operation
      pm - the precision model to use
      Returns:
      the result of the overlay operation

    • overlay

      public static Geometry overlay(Geometry geom0, Geometry geom1, int opCode, PrecisionModel pm, Noder noder)
      Computes an overlay operation on the given geometry operands, using a supplied Noder.
      Parameters:
      geom0 - the first geometry argument
      geom1 - the second geometry argument
      opCode - the code for the desired overlay operation
      pm - the precision model to use (which may be null if the noder does not use one)
      noder - the noder to use
      Returns:
      the result of the overlay operation

    • overlay

      public static Geometry overlay(Geometry geom0, Geometry geom1, int opCode, Noder noder)
      Computes an overlay operation on the given geometry operands, using a supplied Noder.
      Parameters:
      geom0 - the first geometry argument
      geom1 - the second geometry argument
      opCode - the code for the desired overlay operation
      noder - the noder to use
      Returns:
      the result of the overlay operation

    • overlay

      public static Geometry overlay(Geometry geom0, Geometry geom1, int opCode)
      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.

      Parameters:
      geom0 - the first argument geometry
      geom1 - the second argument geometry
      opCode - the code for the desired overlay operation
      Returns:
      the result of the overlay operation

    • setStrictMode

      public void setStrictMode(boolean isStrictMode)
      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
      Parameters:
      isStrictMode - true if strict mode is to be used

    • setOptimized

      public void setOptimized(boolean isOptimized)
      Sets whether overlay processing optimizations are enabled. It may be useful to disable optimizations for testing purposes. Default is TRUE (optimization enabled).
      Parameters:
      isOptimized - whether to optimize processing

    • setOutputEdges

      public void setOutputEdges(boolean isOutputEdges)
      Parameters:
      isOutputEdges -

    • setOutputNodedEdges

      public void setOutputNodedEdges(boolean isOutputNodedEdges)

    • setOutputResultEdges

      public void setOutputResultEdges(boolean isOutputResultEdges)

    • getResult

      public Geometry getResult()
      Gets the result of the overlay operation.
      Returns:
      the result of the overlay operation.
      Throws:
      IllegalArgumentException - if the input is not supported (e.g. a mixed-dimension geometry)
      TopologyException - if a robustness error occurs

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