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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.


HARN Regions

State File
Alabama alhpgn
Arizona azhpgn
Arkansas arhpgn
California North (above 37 degrees) cnhpgn
California South (below 37 degrees) cshpgn
Colorado cohpgn
Connecticut nehpgn
Delaware mdhpgn
Florida flhpgn
Georgia gahpgn
Hawaii hihpgn
Idaho and Montana East (east of 113 degrees) emhpgn
Idaho and Montana East (west of 113 degrees) wmhpgn
Illinois ilhpgn
Indiana inhpgn
Iowa iahpgn
Kansas kshpgn
Kentucky kyhpgn
Louisiana lahpgn
Maine mehpgn
Maryland mdhpgn
Massachusetts nehpgn
Michigan mihpgn
Minnesota mnhpgn
Mississippi mshpgn
Missouri mohpgn
Nebraska nbhpgn
Nevada nvhpgn
New Hampshire nehpgn
New Jersey njhpgn
New Mexico nmhpgn
New York nyhpgn
North Carolina nchpgn
North Dakota ndhpgn
Ohio ohhpgn
Oklahoma okhpgn
Oregon wohpgn
Pennsylvania pahpgn
Puerto Rico and Virgin Islands pvhpgn
Rhode Island nehpgn
South Carolina schpgn
South Dakota sdhpgn
Tennessee tnhpgn
Texas East (east of 100 degrees) ethpgn
Texas West (west of 100 degrees) wthpgn
Utah uthpgn
Vermont nehpgn
Virginia vahpgn
Washington wohpgn
West Virginia wvhpgn
Wisconsin wihpgn
Wyoming wyhpgn

NADCON

When you have to cover larger areas, it is also possible to use NADCON instead.
It uses less grid files with a lower grid density.