Class 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 NameAreaSource DatumAccuracy at 67% confidence (m)
    CONUSConterminous U S (lower 48 states)NAD270.15
    ALASKAAlaska, incl. Aleutian IslandsNAD270.5
    HAWAIIHawaiian IslandsOld Hawaiian (4135)0.2
    STLRNCSt. Lawrence Is., AKSt. Lawrence Island (4136)--
    STPAUL St. Paul Is., AKSt. Paul Island (4137)--
    STGEORGESt. George Is., AKSt. George Island (4138)--
    PRVIPuerto Rico and the Virgin IslandsPuerto 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:

    Since:
    2.1
    Author:
    Rueben Schulz
    See Also:
    NADCON - North American Datum Conversion Utility, Serialized Form
    • 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

      • 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.
      • 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