Class EarthGravitationalModel

  • All Implemented Interfaces:

    public final class EarthGravitationalModel
    extends VerticalTransform
    Transforms vertical coordinates using coefficients from the Earth Gravitational Model.

    This class is an adaption of Fortran code clenqt.for from the National Geospatial-Intelligence Agency and available in public domain. The normalized geopotential coefficients file bundled in this module is an adaptation of egm180.nor file, with some spaces trimmed.

    Pierre Cardinal, Martin Desruisseaux
    • Method Detail

      • load

        protected void load​(String filename)
                     throws IOException
        Loads the coefficients from the specified ASCII file and initialize the internal clenshaw arrays.

        Note: ASCII may looks like an unefficient format for binary distribution. A binary file with coefficient values read by DataInput.readDouble() would be more compact than an uncompressed ASCII file. However, binary files are hard to compress by the ZIP algorithm. Our experience show that a 675 kb uncompressed ASCII file is only 222 kb after ZIP or JAR compression. The same data as a binary file is 257 kb uncompressed and 248 kb compressed. So surprisingly, the ASCII file is more compact than the binary file after compression. Since it is the primary format provided by the Earth-Info web site, we use it directly in order to avoid a multiplication of formats.

        filename - The filename (e.g. "WGS84.cof", relative to this class directory.
        IOException - if the file can't be read or has an invalid content.
      • heightOffset

        public double heightOffset​(double longitude,
                                   double latitude,
                                   double height)
                            throws TransformException
        Returns the value to add to a height above the ellipsoid in order to get a height above the geoid for the specified geographic coordinate.
        Specified by:
        heightOffset in class VerticalTransform
        longitude - The geodetic longitude, in decimal degrees.
        latitude - The geodetic latitude, in decimal degrees.
        height - The height above the ellipsoid in metres.
        The value to add in order to get the height above the geoid (in metres).
        TransformException - if the offset can't be computed for the specified coordinates.