Being “star” based, one of the many things GPS has reinforced is the fact that the physical Earth is a dynamic structure, continually changing shape and dimension over time.  This means of course that any given measurements of the Earth must be considered not in three dimensions (XYZ) but in four (XYZ and Time).  Since the satellites in the GPS system are not conditional on the local movement of the Earth, that presents surveyors with a relatively new set of problems when using established coordinate systems such as State Plane and UTM or even user defined systems based on “accurate” global values (latitude, longitude and ellipsoid height).  As more and more spatial information is integrated into our daily lives (GIS, location based services, etc) the disparities between a “fixed” measuring platform and a constantly changing target become more acute.  This document will be confined in a general way to the two most basic Earth changes (the movement of the center of mass of the Earth and shifts in the “local” Earth surface) and specifically how this movement is realized and dealt with in the Trimble Business Center (TBC) software. Click on the link below to read more about the difference between NAD83 CORS96 and NAD 83 2011

Click for more NAD83 CORS96 vs NAD83 2011

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