HARN - High Accuracy Reference Network

A HARN is a state wide or regional upgrade in accuracy (6-8cm) of NAD 83 coordinates using Global Positioning System (GPS) observations. The datum used with HARN is NAD83(HARN). The HARN grid shift files are used to convert between NAD83 and NAD83(HARN) coordinates. To get the actual datum shift for a coordinate, the 4 closest known coordinates are retrieved from a grid file, and then interpolated using bi-linear interpolation.

HARN Files

For each HARN zone, 2 separate files are needed to calculate the shift. One file containing the latitude shifts (.LAS extension), and a file containing the longitude shifts (.LOS extension). Each file is binary encoded, and contains a header with some information on the file, like rows and columns, bounding rectangle and the grid spacing. The header contents should be the same for both the .los and .las file. Depending on the extension (.las or .los) the file also contains the latitude or longitude datum shifts (in seconds) encoded as 4 byte floating point values. HARN files are provided by the National Geodetic Survey.