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NAD 83 Re-adjustments
NAD 83 Re-adjustments
NAD 83 Re-adjustments
Comparing NAD 83/86, NAD 83/90, and NAD 83/99
First North American Datum of 1983 (NAD 83), later called NAD 83/86 because of the release date and additional re-adjustments, is the horizontal
datum that is used by the United States, Canada, Mexico, and Central America and was established in 1983 and released to the public in 1986,
thus NAD 83/86, by the National Geodetic Survey (NGS) not USGS. NGS defines all datums used by the civilian community and is approved by the
Congress of the U.S. as the
only civilian datum accepted by the U.S. Government. This datum is based on
the Geodetic Reference System 1980 (GRS80) which is defined as the geocentric center of the earth.
As for the High Precision Geodetic Network (HPGN), this is what Florida first called the network (Florida High Precision Geodetic Network)
when it was re-observed in 1988 and 1989 by the National Geodetic Survey (NGS). NGS then re-adjusted the stations observed in Florida and
called it NAD 83 re-adjustment of 1990 (NAD 83/90). This has nothing to do with the Vertical Datum which is completely different. There was
no change in the definition of the horizontal datum only a name change based on the year of the re-adjustment. After Florida was completed
several states wanted the more accurate positions that were being observed by GPS so NGS came up with the name High Accuracy Reference Network
(HARN) which is the term used nationally. This name has been dropped, as well as HPGN, and only a year is assigned to the NAD 83 for each
of the states. Florida has had a couple of re-adjustments with the most notable being NAD 83/90 which differs from the original NAD 83
adjustment by +/- 40 centimeters. The next notable re-adjustment is NAD 83/99 which differs from the NAD 83/90 by +/- 5 centimeters.
Without getting deep into the science behind all this you can go to the NGS
website www.ngs.noaa.gov and look under FAQ for
additional information.
For more information contact:
Ronnie L. Taylor
NOAA, National Geodetic Survey
National Ocean Service Advisor
3900 Commonwealth Blvd., MS105
Tallahassee, Florida 32399
Phone: (850)245-2606
Fax: (850)245-2645
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