Class SpatialPrefixTree

  • Direct Known Subclasses:
    GeohashPrefixTree, NumberRangePrefixTree, QuadPrefixTree, S2PrefixTree

    public abstract class SpatialPrefixTree
    extends Object
    A spatial Prefix Tree, or Trie, which decomposes shapes into prefixed strings at variable lengths corresponding to variable precision. Each string corresponds to a rectangular spatial region. This approach is also referred to "Grids", "Tiles", and "Spatial Tiers".

    Implementations of this class should be thread-safe and immutable once initialized.

    WARNING: This API is experimental and might change in incompatible ways in the next release.
    • Field Detail

      • maxLevels

        protected final int maxLevels
      • ctx

        protected final org.locationtech.spatial4j.context.SpatialContext ctx
    • Constructor Detail

      • SpatialPrefixTree

        public SpatialPrefixTree​(org.locationtech.spatial4j.context.SpatialContext ctx,
                                 int maxLevels)
    • Method Detail

      • getSpatialContext

        public org.locationtech.spatial4j.context.SpatialContext getSpatialContext()
      • getMaxLevels

        public int getMaxLevels()
      • getLevelForDistance

        public abstract int getLevelForDistance​(double dist)
        Returns the level of the largest grid in which its longest side is less than or equal to the provided distance (in degrees). Consequently dist acts as an error epsilon declaring the amount of detail needed in the grid, such that you can get a grid with just the right amount of precision.
        dist - >= 0
        level [1 to maxLevels]
      • getDistanceForLevel

        public abstract double getDistanceForLevel​(int level)
        Given a cell having the specified level, returns the distance from opposite corners. Since this might vary depending on where the cell is, this method may over-estimate.
        level - [1 to maxLevels]
        > 0
      • getWorldCell

        public abstract Cell getWorldCell()
        Returns the level 0 cell which encompasses all spatial data. Equivalent to readCell(BytesRef,Cell) with no bytes.
      • readCell

        public abstract Cell readCell​(BytesRef term,
                                      Cell scratch)
        This creates a new Cell (or re-using scratch if provided), initialized to the state as read by the bytes. Warning: An implementation may refer to the same byte array (no copy). If Cell.setLeaf() is subsequently called, it would then modify these bytes.
      • getTreeCellIterator

        public CellIterator getTreeCellIterator​(org.locationtech.spatial4j.shape.Shape shape,
                                                int detailLevel)
        Gets the intersecting cells for the specified shape, without exceeding detail level. If a cell is within the query shape then it's marked as a leaf and none of its children are added. For cells at detailLevel, they are marked as leaves too, unless it's a point.

        IMPORTANT: Cells returned from the iterator can be re-used for cells at the same level. So you can't simply iterate to subsequent cells and still refer to the former cell nor the bytes returned from the former cell, unless you know the former cell is a parent.

        shape - the shape; possibly null but the caller should liberally call remove() if so.
        detailLevel - the maximum detail level to get cells for
        the matching cells