NGS Methods
NADCON5
NADCON5 is a replacement for NADCON and GEOCON methods. It uses a biquadratic interpolation method. (Other interpolation methods are available for custom definitions. The shift values for latitude, longitude and height are stored in grid files (nadcon5.*.b).
For more information see https://www.ngs.noaa.gov/NADCON5/index.shtml
Note: The definition of datum transformations using this method includes parameters specifying the required grid files. If the system cannot find the specified file, the shift will be marked unusable in the Datasource and may not be selected for use.
NADCON
The NGS NADCON method applies a simple interpolation algorithm using a gridded set of standard datum transformations as parameters. The shift values for a geographic area are stored in a set of grid files, one representing latitude shifts (named with the extension .las) and one representing longitude shifts (named with the extension .los). This transformation uses bilinear interpolation (other interpolation types are available for custom definitions).
The NGS NADCON method transforms coordinate values between the North American Datum of 1927 (NAD 27) and the North American Datum of 1983 (NAD 83). The NGS NADCON method provides a transformation that is accurate to within 0.15-0.5 meters. (Please refer to NOAA Technical Memorandum NOS NGS-50 "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.")
The Geographic Calculator uses grid files in a format published and provided by the National Geodetic Survey. Questions about the availability of other NADCON grid files (and the NGS NADCON method in general) should be addressed to:
Address:
National Geodetic Survey
Phone: (301) 713-3242
Note: The definition of datum transformations using this method includes parameters specifying the required grid files. If the system cannot find the specified file, the shift will be marked unusable in the Datasource and may not be selected for use.
NGS HARN/ HPGN
The Geographic Calculator supports the definition of a geodetic datum based on a NGS High Accuracy Reference Network (HARN). The National Geodetic Survey is establishing HARNs within the U.S. on a state-by-state basis.
You can think of a HARN as a geodetic datum, most easily viewed as an enhanced NAD83 datum. HARNs are also known as NAD83/91 and High Precision Grid Networks (HPGN).
The NGS HARN method is actually very similar to the NGS NADCON method. As with the NADCON method, the shift values for a geographic area are stored in a set of grid files, one representing latitude shifts (named with the extension .las) and one representing longitude shifts (named with the extension .los). The major difference is that the HARN data files contain shifts from NAD83 to a HARN instead of NAD27 to NAD83. This transformation uses bilinear interpolation.
The Geographic Calculator uses grid files in a format published and provided by the National Geodetic Survey. Questions about the availability of other HARN grid files (and the HARN systems in general) should be addressed to:
The current HARNs are already pre-defined within the Geographic Calculator. As new HARNs are completed and made available, they will be added to Geodata.xml. These updated versions will be available for download from our website at www.bluemarblegeo.com
Note: The definition of datum transformations using this method includes parameters specifying the required grid files. If the system cannot find the specified file, the shift will be marked unusable in the Datasource and can not be selected for use.
GEOCON
The GEOCON method transforms NAD83 (HARN) to NAD83(nsrs2007) and NAD83(nsrs2007) to NAD83(2011). The GEOCON method uses Quadratic Interpolation (Other interpolation methods are available for custom definitions). The shift values for latitude, longitude and height are stored in grid files (*.b).
For more information see: