Class BufferInputLineSimplifier

java.lang.Object
org.locationtech.jts.operation.buffer.BufferInputLineSimplifier

public class BufferInputLineSimplifier extends Object
Simplifies a buffer input line to remove concavities with shallow depth.

The most important benefit of doing this is to reduce the number of points and the complexity of shape which will be buffered. It also reduces the risk of gores created by the quantized fillet arcs (although this issue should be eliminated in any case by the offset curve generation logic).

A key aspect of the simplification is that it affects inside (concave or inward) corners only. Convex (outward) corners are preserved, since they are required to ensure that the generated buffer curve lies at the correct distance from the input geometry.

Another important heuristic used is that the end segments of the input are never simplified. This ensures that the client buffer code is able to generate end caps faithfully.

No attempt is made to avoid self-intersections in the output. This is acceptable for use for generating a buffer offset curve, since the buffer algorithm is insensitive to invalid polygonal geometry. However, this means that this algorithm cannot be used as a general-purpose polygon simplification technique.

  • Field Details

    • INIT

      private static final int INIT
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    • DELETE

      private static final int DELETE
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    • KEEP

      private static final int KEEP
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    • inputLine

      private Coordinate[] inputLine
    • distanceTol

      private double distanceTol
    • isDeleted

      private byte[] isDeleted
    • angleOrientation

      private int angleOrientation
    • NUM_PTS_TO_CHECK

      private static final int NUM_PTS_TO_CHECK
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  • Constructor Details

    • BufferInputLineSimplifier

      public BufferInputLineSimplifier(Coordinate[] inputLine)
  • Method Details

    • simplify

      public static Coordinate[] simplify(Coordinate[] inputLine, double distanceTol)
      Simplify the input coordinate list. If the distance tolerance is positive, concavities on the LEFT side of the line are simplified. If the supplied distance tolerance is negative, concavities on the RIGHT side of the line are simplified.
      Parameters:
      inputLine - the coordinate list to simplify
      distanceTol - simplification distance tolerance to use
      Returns:
      the simplified coordinate list
    • simplify

      public Coordinate[] simplify(double distanceTol)
      Simplify the input coordinate list. If the distance tolerance is positive, concavities on the LEFT side of the line are simplified. If the supplied distance tolerance is negative, concavities on the RIGHT side of the line are simplified.
      Parameters:
      distanceTol - simplification distance tolerance to use
      Returns:
      the simplified coordinate list
    • deleteShallowConcavities

      private boolean deleteShallowConcavities()
      Uses a sliding window containing 3 vertices to detect shallow angles in which the middle vertex can be deleted, since it does not affect the shape of the resulting buffer in a significant way.
      Returns:
    • findNextNonDeletedIndex

      private int findNextNonDeletedIndex(int index)
      Finds the next non-deleted index, or the end of the point array if none
      Parameters:
      index -
      Returns:
      the next non-deleted index, if any or inputLine.length if there are no more non-deleted indices
    • collapseLine

      private Coordinate[] collapseLine()
    • isDeletable

      private boolean isDeletable(int i0, int i1, int i2, double distanceTol)
    • isShallowConcavity

      private boolean isShallowConcavity(Coordinate p0, Coordinate p1, Coordinate p2, double distanceTol)
    • isShallowSampled

      private boolean isShallowSampled(Coordinate p0, Coordinate p2, int i0, int i2, double distanceTol)
      Checks for shallowness over a sample of points in the given section. This helps prevents the simplification from incrementally "skipping" over points which are in fact non-shallow.
      Parameters:
      p0 - start coordinate of section
      p2 - end coordinate of section
      i0 - start index of section
      i2 - end index of section
      distanceTol - distance tolerance
      Returns:
    • isShallow

      private boolean isShallow(Coordinate p0, Coordinate p1, Coordinate p2, double distanceTol)
    • isConcave

      private boolean isConcave(Coordinate p0, Coordinate p1, Coordinate p2)