Package org.openstreetmap.josm.data.projection.datum

Class NTV2GridShiftFile

  • All Implemented Interfaces:
    java.io.Serializable
    public class NTV2GridShiftFile
extends java.lang.Object
implements java.io.Serializable
    Models the NTv2 format Grid Shift File and exposes methods to shift coordinate values using the Sub Grids contained in the file.

    The principal reference for the algorithms used is the 'GDAit Software Architecture Manual' produced by the Geomatics Department of the University of Melbourne

    This library reads binary NTv2 Grid Shift files in Big Endian (Canadian standard) or Little Endian (Australian Standard) format. The older 'Australian' binary format is not supported, only the official Canadian format, which is now also used for the national Australian Grid.

    Grid Shift files can be read as InputStreams or RandomAccessFiles. Loading an InputStream places all the required node information (accuracy data is optional) into heap based Java arrays. This is the highest performance option, and is useful for large volume transformations. Non-file data sources (eg using an SQL Blob) are also supported through InputStream. The RandomAccessFile option has a much smaller memory footprint as only the Sub Grid headers are stored in memory, but transformation is slower because the file must be read a number of times for each transformation.

    Coordinates may be shifted Forward (ie from and to the Datums specified in the Grid Shift File header) or Reverse. The reverse transformation uses an iterative approach to approximate the Grid Shift, as the precise transformation is based on 'from' datum coordinates.

    Coordinates may be specified either in Seconds using Positive West Longitude (the original NTv2 arrangement) or in decimal Degrees using Positive East Longitude.

    Since:
    2507
    See Also:
    Serialized Form

    • Method Detail

      • readBytes

        private static void readBytes​(java.io.InputStream in,
                              byte[] b)
                       throws java.io.IOException
        Throws:
        java.io.IOException

      • loadGridShiftFile

        public void loadGridShiftFile​(java.io.InputStream in,
                              boolean loadAccuracy)
                       throws java.io.IOException
        Load a Grid Shift File from an InputStream. The Grid Shift node data is stored in Java arrays, which will occupy about the same memory as the original file with accuracy data included, and about half that with accuracy data excluded. The size of the Australian national file is 4.5MB, and the Canadian national file is 13.5MB

        The InputStream is closed by this method.

        Parameters:
        in - Grid Shift File InputStream
        loadAccuracy - is Accuracy data to be loaded as well as shift data?
        Throws:
        java.io.IOException - if any I/O error occurs

      • createSubGridTree

        private static NTV2SubGrid[] createSubGridTree​(NTV2SubGrid... subGrid)
        Create a tree of Sub Grids by adding each Sub Grid to its parent (where it has one), and returning an array of the top level Sub Grids
        Parameters:
        subGrid - an array of all Sub Grids
        Returns:
        an array of top level Sub Grids with lower level Sub Grids set.

      • gridShiftForward

        public boolean gridShiftForward​(NTV2GridShift gs)
        Shift a coordinate in the Forward direction of the Grid Shift File.
        Parameters:
        gs - A GridShift object containing the coordinate to shift
        Returns:
        True if the coordinate is within a Sub Grid, false if not

      • gridShiftReverse

        public boolean gridShiftReverse​(NTV2GridShift gs)
        Shift a coordinate in the Reverse direction of the Grid Shift File.
        Parameters:
        gs - A GridShift object containing the coordinate to shift
        Returns:
        True if the coordinate is within a Sub Grid, false if not

      • getSubGrid

        private static NTV2SubGrid getSubGrid​(NTV2SubGrid[] topLevelSubGrid,
                                      double lon,
                                      double lat)
        Find the finest SubGrid containing the coordinate, specified in Positive West Seconds
        Parameters:
        topLevelSubGrid - top level subgrid
        lon - Longitude in Positive West Seconds
        lat - Latitude in Seconds
        Returns:
        The SubGrid found or null

      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object

      • getFromEllipsoid

        public java.lang.String getFromEllipsoid()
        Returns "from" ellipsoid identifier.
        Returns:
        "from" ellipsoid identifier

      • getToEllipsoid

        public java.lang.String getToEllipsoid()
        Returns "to" ellipsoid identifier.
        Returns:
        "to" ellipsoid identifier