Package cds.healpix

Class HealpixNestedFast

  • All Implemented Interfaces:
    HashComputer, HierarchyItem, NeighbourSelector, VerticesAndPathComputer
    public final class HealpixNestedFast
extends java.lang.Object
implements HashComputer, VerticesAndPathComputer, NeighbourSelector
    A faster, thread-safe, but ugly (sorry: less readable) version of HealpixNested. The code has also been "denormalise" to try to be faster: we introduce redundancy by suppressing method calls when a method must return more than one elements, ... Motivations: in Java, all arguments of a function are passed-by-value. And, like most languages, a function returns only one output. It means that if, e.g. a function as to return a pair of coordinate you have only two solutions: the first one is to instantiate an object containing the pair of coordinates and return it, or the method have to take an object and set the pair of coordinates. In this "fast version", we duplicate code to avoid creating objects inside critical methods and we write the results in arguments instead of returning new objects. The instantiation of an object in Java is cheap, but it cost is not negligible compared to the speed of HEALPix methods.
    Author:
    F.-X. Pineau

    • Field Detail

      • D0H_NEIGHBOURS

        public static final byte[][] D0H_NEIGHBOURS
        For each of the 12 hash of depth 0, contains the list of the depth 0 neighbours sorted by increasing hash value.

      • NEIGHBOURS

        public static final byte[][][] NEIGHBOURS

    • Constructor Detail

      • HealpixNestedFast

        public HealpixNestedFast​(int depth,
                         FillingCurve2DType fillingCurveType)

    • Method Detail

      • hash

        public long hash​(double lonRad,
                 double latRad)
        Description copied from interface: HashComputer
        Returns the HEALPix hash value of the given coordinate at this object depth. WARNING: depending on the implementation, this method may or may not be thread-safe.
        Specified by:
        hash in interface HashComputer
        Parameters:
        lonRad - longitude in radians, must support reasonably large positive and negative values producing accurate results with a naive range reduction like modulo 2*pi (i.e. without having to resort on Cody-Waite or Payne Hanek range reduction).
        latRad - latitude in [-pi/2, pi/2] radians
        Returns:
        the hash value associated to the given coordinate, at this object depth.

      • center

        public double[] center​(long hash)
        Description copied from interface: VerticesAndPathComputer
        Compute the position on the unit sphere of the center (in the Euclidean projection plane) of the cell associated to the given hash value.
        Specified by:
        center in interface VerticesAndPathComputer
        Parameters:
        hash - hash value of the cell we look for the unprojected center
        Returns:
        the unprojected position (on the unit sphere) of the center of the cell in the Euclidean plane. The lon and lat coordinate are stored in the returned array at indices VerticesAndPathComputer.LON_INDEX and VerticesAndPathComputer.LAT_INDEX respectively. Lat in [-pi/2, pi/2] radians, lon is in [0, 2pi] radians.

      • vertex

        public double[] vertex​(long hash,
                       CompassPoint.Cardinal cardinalPoint)
        Description copied from interface: VerticesAndPathComputer
        Compute the position of an HEALPix cell vertex on the unit sphere.
        Specified by:
        vertex in interface VerticesAndPathComputer
        Parameters:
        hash - hash value of the cell we look for the given vertex.
        cardinalPoint - location of the vertex with respect to the cell center
        Returns:
        the position (on the unit sphere) of the vertex located at the given cardinal direction from the center of the given cell. The lon and lat coordinate are stored in the returned array at indices VerticesAndPathComputer.LON_INDEX and VerticesAndPathComputer.LAT_INDEX respectively. Lat is in [-pi/2, pi/2] radians, lon is in [0, 2pi] radians.

      • vertices

        public java.util.EnumMap<CompassPoint.Cardinal,​double[]> vertices​(long hash,
                                                                        java.util.EnumSet<CompassPoint.Cardinal> cardinalPoints)
        Description copied from interface: VerticesAndPathComputer
        Returns the vertices located at the given cardinal points. If you want the full 4 vertices, simply use EnumSet.allOf(Cardinal). For West and East vertices, use EnumSet.of(Cardinal.W, Cardinal.E).
        Specified by:
        vertices in interface VerticesAndPathComputer
        Parameters:
        hash - hash value of the cell we look for the given vertices.
        cardinalPoints - locations of the vertices we look for the positions
        Returns:
        the positions (on the unit sphere) of the vertices located at the given cardinal directions from the center of the given cell. The lon and lat coordinates of each vertex are stored in the arrays at indices VerticesAndPathComputer.LON_INDEX and VerticesAndPathComputer.LAT_INDEX respectively. Lat is in [-pi/2, pi/2] radians, lon is in [0, 2pi] radians.

      • vertices

        public void vertices​(long hash,
                     java.util.EnumMap<CompassPoint.Cardinal,​double[]> cardinalPoints)
        Description copied from interface: VerticesAndPathComputer
        See VerticesAndPathComputer.vertices(long, EnumSet). The difference is that the user provides a pre-set Map. The structure of the Map is not modified, but the coordinates of the values (array values) are overwritten. An error will be thrown if a value is null or contains less than two elements.
        Specified by:
        vertices in interface VerticesAndPathComputer
        Parameters:
        hash - hash value of the cell we look for the given vertices.
        cardinalPoints - the map to be modified y

      • pathAlongCellSide

        public double[][] pathAlongCellSide​(long hash,
                                    CompassPoint.Cardinal fromVertex,
                                    CompassPoint.Cardinal toVertex,
                                    boolean isToVertexIncluded,
                                    int nSegments)
        Description copied from interface: VerticesAndPathComputer
        Compute points on a given side of a given HEALPix cell on the unit sphere.
        Specified by:
        pathAlongCellSide in interface VerticesAndPathComputer
        Parameters:
        hash - hash value of the cell we look for side path on the unit sphere.
        fromVertex - direction (from the cell center) of the path starting vertex
        toVertex - direction (from the cell center) of the path ending vertex
        isToVertexIncluded - if false, the result contains nSegments points and do no include the result ending vertex. Else the result contains nSegments + 1 points.
        nSegments - number of segments in the path from the starting vertex to the ending vertex
        Returns:
        a list of points on the given side of the given HEALPix cell on the unit sphere.

      • pathAlongCellSide

        public void pathAlongCellSide​(long hash,
                              CompassPoint.Cardinal fromVertex,
                              CompassPoint.Cardinal toVertex,
                              boolean isToVertexIncluded,
                              int nSegments,
                              double[][] pathPoints)
        Description copied from interface: VerticesAndPathComputer
        See VerticesAndPathComputer.pathAlongCellSide(long, Cardinal, Cardinal, boolean, int). The difference is that the user provides a list of points whose coordinates are going to be overwritten. An error will be thrown if the array (of array) is not large enough (i.e. its is smaller than nSegments or nSegments + 1) or if one of the array is null or contains less than two elements.
        Specified by:
        pathAlongCellSide in interface VerticesAndPathComputer
        Parameters:
        hash - hash value of the cell we look for side path on the unit sphere.
        fromVertex - direction (from the cell center) of the path starting vertex
        toVertex - direction (from the cell center) of the path ending vertex
        isToVertexIncluded - if false, the result contains nSegments points and do no include the result ending vertex. Else the result contains nSegments + 1 points.
        nSegments - number of segments in the path from the starting vertex to the ending vertex
        pathPoints - object used to store the result.

      • pathAlongCellEdge

        public double[][] pathAlongCellEdge​(long hash,
                                    CompassPoint.Cardinal startingVertex,
                                    boolean clockwiseDirection,
                                    int nSegmentsBySide)
        Specified by:
        pathAlongCellEdge in interface VerticesAndPathComputer
        Parameters:
        hash - hash value of the cell we look for the edge path on the unit sphere.
        startingVertex - direction (from the cell center) of the path starting vertex
        clockwiseDirection - if true, result points are stored in a clockwise direction order, else they are stored in counter-clockwise direction order.
        nSegmentsBySide - number of segments in each each side is divided. Hence, the total number of points in the result is 4 x nSegmentsBySide.
        Returns:
        a list of points on the given edge of the given HEALPix cell on the unit sphere, clockwise or counter-clockwise ordered.

      • pathAlongCellEdge

        public void pathAlongCellEdge​(long hash,
                              CompassPoint.Cardinal startingVertex,
                              boolean clockwiseDirection,
                              int nSegmentsBySide,
                              double[][] pathPoints)
        Description copied from interface: VerticesAndPathComputer
        See VerticesAndPathComputer.pathAlongCellEdge(long, Cardinal, boolean, int). The difference is that the user provides a list of points whose coordinates are going to be overwritten. An error will be thrown if the array (of array) is not large enough (i.e. its is smaller than 4 *nSegments) or if one of the array is null or contains less than two elements.
        Specified by:
        pathAlongCellEdge in interface VerticesAndPathComputer
        Parameters:
        hash - hash hash value of the cell we look for the edge path on the unit sphere.
        startingVertex - direction (from the cell center) of the path starting vertex
        clockwiseDirection - if true, result points are stored in a clockwise direction order, else they are stored in counter-clockwise direction order.
        nSegmentsBySide - number of segments in each each side is divided. Hence, the total number of points in the result is 4 x nSegmentsBySide.
        pathPoints - object used to store the result.

      • neighbour

        public long neighbour​(long hash,
                      CompassPoint.MainWind direction)
        Description copied from interface: NeighbourSelector
        The hash value of the neighbour of the cell of given hash, in the given deirection.
        Specified by:
        neighbour in interface NeighbourSelector
        Parameters:
        hash - ash value of the cell we are looking for the neighbour.
        direction - direction of the neighbour we are looking for.
        Returns:
        -1 if there is no neighbour in the given direction (hashes located at corners of base hases).

      • neighbours

        public NeighbourList neighbours​(long hash)
        Description copied from interface: NeighbourSelector
        Returns the list of the hash of the cells surrounding the cell defined by the given hash. The number of surrounding cells can be 8 (for all cells except the cells located at the corners of the 12 depth 0 cells), 7 (for the west and east corners of the polar caps, i.e. depth 0 cells number 0, 1, 2, 4, 8, 9, 10 and 11, or for the north and south corners of the equatorial regions, i.e. depth 0 cells number 4, 5, 6 and 7), or 6 for depth 0 pixels.
        Specified by:
        neighbours in interface NeighbourSelector
        Parameters:
        hash - hash value of the cell we are looking for the neighbours.
        Returns:
        the list of neighbours hashes

      • neighbours

        public void neighbours​(long hash,
                       NeighbourList result)
        Description copied from interface: NeighbourSelector
        Equivalent of NeighbourSelector.neighbours(long) but passing in argument the list object to be filled. WARNING: the content of the provided list is overwritten, and be sure the list is large enough (at least of size 8). And the value -1 is returned if the given hash has no neighbour at the given main wind direction.
        Specified by:
        neighbours in interface NeighbourSelector
        Parameters:
        hash - the hash code we want the neighbours
        result - which contains the list of neighbours from index 0 to the number of neighbours

      • neighbours

        public void neighbours​(long hash,
                       java.util.EnumSet<CompassPoint.MainWind> directions,
                       NeighbourList result)
        Description copied from interface: NeighbourSelector
        Equivalent of NeighbourSelector.neighbours(long, FlatHashList) but with the list of direction of the wanted neighbours. And the value -1 is returned if the given hash has no neighbour at the given main wind direction.
        Specified by:
        neighbours in interface NeighbourSelector
        Parameters:
        hash - hash value of the cell we are looking for the neighbours.
        directions - the directions of the neighbours we are looking for.
        result - the list holding the result.