Class BufferInputLineSimplifier


  • public class BufferInputLineSimplifier
    extends java.lang.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.

    • Constructor Detail

      • BufferInputLineSimplifier

        public BufferInputLineSimplifier​(Coordinate[] inputLine)
    • Method Detail

      • 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)
      • 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: