au.com.objectix.jgridshift
Class GridShiftFile

java.lang.Object
  au.com.objectix.jgridshift.GridShiftFile

All Implemented Interfaces:

java.io.Serializable

public class GridShiftFile

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 alogrithms 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 perfomance option, and is useful for large volume transformations. Non-file data sources (eg using an SQL Blob) are also supported through InputStream. The RandonAccessFile 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.

Author:

Peter Yuill

See Also:

Serialized Form

Constructor Summary

GridShiftFile()

Method Summary

java.lang.String	getFromEllipsoid()
SubGrid[]	getSubGridTree() Get a copy of the SubGrid tree for this file.
java.lang.String	getToEllipsoid()
boolean	gridShiftForward(GridShift gs) Shift a coordinate in the Forward direction of the Grid Shift File.
boolean	gridShiftReverse(GridShift gs) Shift a coordinate in the Reverse direction of the Grid Shift File.
boolean	isLoaded()
void	loadGridShiftFile(java.io.InputStream in, boolean loadAccuracy) Load a Grid Shift File from an InputStream.
void	loadGridShiftFile(java.io.RandomAccessFile raf) Load a Grid Shift File from a RandomAccessFile.
java.lang.String	toString()
void	unload()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

GridShiftFile

public GridShiftFile()

Method Detail

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.lang.Exception

java.io.IOException

loadGridShiftFile

public void loadGridShiftFile(java.io.RandomAccessFile raf)
                       throws java.io.IOException

Load a Grid Shift File from a RandomAccessFile. The Grid Shift node data is not stored in Java arrays, but accessed directly from the file when required.

This method does not close the file.

Parameters:

raf - Grid Shift File

Throws:

java.lang.Exception

java.io.IOException

gridShiftForward

public boolean gridShiftForward(GridShift gs)
                         throws java.io.IOException

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

Throws:

java.io.IOException

gridShiftReverse

public boolean gridShiftReverse(GridShift gs)
                         throws java.io.IOException

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

Throws:

java.io.IOException

isLoaded

public boolean isLoaded()

unload

public void unload()
            throws java.io.IOException

Throws:

java.io.IOException

toString

public java.lang.String toString()

getSubGridTree

public SubGrid[] getSubGridTree()

Get a copy of the SubGrid tree for this file.

Returns:

a deep clone of the current SubGrid tree

getFromEllipsoid

public java.lang.String getFromEllipsoid()

getToEllipsoid

public java.lang.String getToEllipsoid()