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NOAA Datums Videos 2014

Differential correction with NA2011 and the newest epoch of NAD83

See our and Datums Basics and GPS Tutorials for the long-awaited results of months of rigorous testing and peer review

Trimble Positions software has replaced Trimble GPS Analyst in ArcGIS 10.1

ALASKA GPS and GIS users - check out Joel Cusick's Datum and Projections presentation Feb 2013

ArcGIS 10.1 - New and Cool improvements see Presentation from Melita Kennedy, ESRI : Projections and Datums Dec 2012

Home GPS Tutorials Why GPS and GIS data are not in the same reference frame
Why GPS and GIS data are not in the same reference frame PDF Print E-mail


Why GPS and GIS data are not in the same reference frame

1. GPS data collection is WGS84

2. Differential correction is often NAD83

3. Export to GIS in one of millions of possible projections



1. GPS data collection is WGS84

GPS satellites broadcast in WGS-84 and most GPS receivers, including Trimble receivers, RECEIVE DATA only in WGS-84.

2. Differential correction is often NAD83

Since satellites orbits are referenced to one frame and terrestrial control points to other, differential correction of GPS data introduces a mixture of reference systems.

For real-time correction, US Coast Guard beacon (dGPS)and OmniStar VBS signals (in the US) are broadcast in NAD83 (2011). WAAS signals are broadcast in WGS84.

For post-processing, CORS stations coordinates are published in NAD83 (2011, PA11 or MA11).

3. Export to GIS in one of millions of possible projections

Moving your GPS data to or from a GIS potentially introduces an near infinite number of reference system choices.   A recent ESRI list of supported reference frames was 7 pages long!

For example, the US federal government is based in NAD83 so yet another datum gate to pass through.