org.geotools.referencing.operation.transform

Class NADCONTransform

Object

Formattable

AbstractMathTransform

NADCONTransform

All Implemented Interfaces:

Serializable, MathTransform, MathTransform2D

public class NADCONTransform
extends AbstractMathTransform
implements MathTransform2D, Serializable

Transform backed by the North American Datum Conversion grid. The North American Datum Conversion (NADCON) Transform (EPSG code 9613) is a two dimentional datum shift method, created by the National Geodetic Survey (NGS), that uses interpolated values from two grid shift files. This method is used to transform NAD27 (EPSG code 4267) datum coordinates (and some others) to NAD83 (EPSG code 4267) within the United States. There are two set of grid shift files: NADCON and High Accuracy Reference Networks (HARN). NADCON shfts from NAD27 (and some others) to NAD83 while HARN shifts from the NADCON NAD83 to an improved NAD83. Both sets of grid shift files may be downloaded from www.ngs.noaa.gov/PC_PROD/NADCON/.

Some of the NADCON grids, their areas of use, and source datums are shown in the following table.

Shift File Name	Area	Source Datum	Accuracy at 67% confidence (m)
CONUS	Conterminous U S (lower 48 states)	NAD27	0.15
ALASKA	Alaska, incl. Aleutian Islands	NAD27	0.5
HAWAII	Hawaiian Islands	Old Hawaiian (4135)	0.2
STLRNC	St. Lawrence Is., AK	St. Lawrence Island (4136)	--
STPAUL	St. Paul Is., AK	St. Paul Island (4137)	--
STGEORGE	St. George Is., AK	St. George Island (4138)	--
PRVI	Puerto Rico and the Virgin Islands	Puerto Rico (4139)	0.05

Grid shift files come in two formats: binary and text. The files from the NGS are binary and have .las (latitude shift) and .los (longitude shift) extentions. Text grids may be created with the NGS nadgrd program and have .laa (latitude shift) and .loa (longitude shift) file extentions. Both types of files may be used here.

The grid names to use for transforming are parameters of this MathTransform. This parameter may be the full name and path to the grids or just the name of the grids if the default location of the grids was set as a preference. This preference may be set with the main method of this class.

Transformations here have been tested to be within 0.00001 seconds of values given by the NGS ndcon210 program for NADCON grids. American Samoa and HARN shifts have not yet been tested. References:

• NADCONreadme
• American Samoa Grids for NADCON - Samoa_Readme.txt
• NADCON - The Application of Minimum-Curvature-Derived Surfaces in the Transformation of Positional Data From the North American Datum of 1927 to the North American Datum of 1983 - NOAA TM.
• ndcon210.for - NGS fortran source code for NADCON conversions. See the following subroutines: TRANSF, TO83, FGRID, INTRP, COEFF and SURF
• nadgrd.for - NGS fortran source code to export/import binary and text grid formats
• EPSG Geodesy Parameters database version 6.5

Since:

2.1

Author:

Rueben Schulz

See Also:

NADCON - North American Datum Conversion Utility, Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	NADCONTransform.Provider The provider for NADCONTransform.

Field Summary

Fields inherited from class Formattable

SINGLE_LINE

Constructor Summary

Constructors

Constructor and Description
NADCONTransform(URI latGridName, URI longGridName) Constructs a NADCONTransform from the specified grid shift files.

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object object) Compares the specified object with this math transform for equality.
ParameterDescriptorGroup	getParameterDescriptors() Returns the parameter descriptors for this math transform.
ParameterValueGroup	getParameterValues() Returns the parameter values for this math transform.
int	getSourceDimensions() Gets the dimension of input points (always 2).
int	getTargetDimensions() Gets the dimension of output points (always 2).
int	hashCode() Returns a hash value for this transform.
MathTransform2D	inverse() Returns the inverse of this transform.
void	inverseTransform(double[] srcPts, int srcOff, double[] dstPts, int dstOff, int numPts) Transforms nad83 values to nad27.
protected URL	locateGrid(URI uri)
static void	main(String... args) Used to set the preference for the default grid shift file location.
void	transform(double[] srcPts, int srcOff, double[] dstPts, int dstOff, int numPts) Transforms a list of coordinate point ordinal values.

Methods inherited from class AbstractMathTransform

createTransformedShape, derivative, derivative, ensureNonNull, formatWKT, getName, isIdentity, needCopy, normalizeAngle, rollLongitude, transform, transform, transform, transform, transform

Methods inherited from class Formattable

cleanupThreadLocals, toString, toWKT, toWKT, toWKT, toWKT

Methods inherited from class Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface MathTransform2D

createTransformedShape, derivative, transform

Methods inherited from interface MathTransform

derivative, isIdentity, toWKT, transform, transform, transform, transform

Constructor Detail

NADCONTransform

public NADCONTransform(URI latGridName,
                       URI longGridName)
                throws ParameterNotFoundException,
                       FactoryException

Constructs a NADCONTransform from the specified grid shift files.

Parameters:

latGridName - path and name (or just name if GRID_LOCATION is set) to the latitude difference file. This will have a .las or .laa file extention.

longGridName - path and name (or just name if GRID_LOCATION is set) to the longitude difference file. This will have a .los or .loa file extention.

Throws:

ParameterNotFoundException - if a math transform parameter cannot be found.

FactoryException - if there is a problem creating this math transform (ie file extentions are unknown or there is an error reading the grid files)

Method Detail

locateGrid

protected URL locateGrid(URI uri)
                  throws FactoryException

Throws:

FactoryException

getParameterDescriptors

public ParameterDescriptorGroup getParameterDescriptors()

Returns the parameter descriptors for this math transform.

Overrides:

getParameterDescriptors in class AbstractMathTransform

Returns:

The parameter descriptors for this math transform, or null.

See Also:

OperationMethod.getParameters()

getParameterValues

public ParameterValueGroup getParameterValues()

Returns the parameter values for this math transform.

Overrides:

getParameterValues in class AbstractMathTransform

Returns:

A copy of the parameter values for this math transform.

See Also:

Operation.getParameterValues()

getSourceDimensions

public int getSourceDimensions()

Gets the dimension of input points (always 2).

Specified by:

getSourceDimensions in interface MathTransform

Specified by:

getSourceDimensions in class AbstractMathTransform

Returns:

the source dimensions.

getTargetDimensions

public int getTargetDimensions()

Gets the dimension of output points (always 2).

Specified by:

getTargetDimensions in interface MathTransform

Specified by:

getTargetDimensions in class AbstractMathTransform

Returns:

the target dimensions.

transform

public void transform(double[] srcPts,
                      int srcOff,
                      double[] dstPts,
                      int dstOff,
                      int numPts)
               throws TransformException

Transforms a list of coordinate point ordinal values. This method is provided for efficiently transforming many points. The supplied array of ordinal values will contain packed ordinal values. For example, if the source dimension is 3, then the ordinals will be packed in this order: (x₀,y₀,z₀,

x₁,y₁,z₁ ...). All input and output values are in decimal degrees.

Specified by:

transform in interface MathTransform

Parameters:

srcPts - the array containing the source point coordinates.

srcOff - the offset to the first point to be transformed in the source array.

dstPts - the array into which the transformed point coordinates are returned. May be the same than srcPts.

dstOff - the offset to the location of the first transformed point that is stored in the destination array.

numPts - the number of point objects to be transformed.

Throws:

TransformException - if the input point is outside the area covered by this grid.

inverseTransform

public void inverseTransform(double[] srcPts,
                             int srcOff,
                             double[] dstPts,
                             int dstOff,
                             int numPts)
                      throws TransformException

Transforms nad83 values to nad27. Input and output values are in decimal degrees. This is done by itteratively finding a nad27 value that shifts to the input nad83 value. The input nad83 value is used as the first approximation.

Parameters:

srcPts - the array containing the source point coordinates.

srcOff - the offset to the first point to be transformed in the source array.

dstPts - the array into which the transformed point coordinates are returned. May be the same than srcPts.

dstOff - the offset to the location of the first transformed point that is stored in the destination array.

numPts - the number of point objects to be transformed.

Throws:

TransformException - if the input point is outside the area covered by this grid.

inverse

public MathTransform2D inverse()

Returns the inverse of this transform.

Specified by:

inverse in interface MathTransform

Specified by:

inverse in interface MathTransform2D

Overrides:

inverse in class AbstractMathTransform

Returns:

the inverse of this transform

hashCode

public int hashCode()

Description copied from class: AbstractMathTransform

Returns a hash value for this transform.

Overrides:

hashCode in class AbstractMathTransform

equals

public boolean equals(Object object)

Description copied from class: AbstractMathTransform

Compares the specified object with this math transform for equality. The default implementation checks if object is an instance of the same class than this and use the same parameter descriptor. Subclasses should override this method in order to compare internal fields.

Overrides:

equals in class AbstractMathTransform

Parameters:

object - The object to compare with this transform.

Returns:

true if the given object is a transform of the same class and if, given identical source position, the transformed position would be the equals.

main

public static void main(String... args)

Used to set the preference for the default grid shift file location. This allows grids parameters to be specified by name only, without the full path. This needs to be done only once, by the user. Path values may be simple file system paths or more complex text representations of a url. A value of "default" resets this preference to its default value.

Example:

 java org.geotools.referencing.operation.transform.NADCONTransform file:///home/rschulz/GIS/NADCON/data
 

Parameters:

args - a single argument for the defualt location of grid shift files