Spectra Precision Survey Pro v4.6 Ranger User Manual User Manual

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GPS Overview

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then run across the country and closed on the opposite coast. This

datum contained a number of systematic errors including un-modeled

local gravity effects and refraction errors. Also, it was later discovered
that the “mean sea level” from the Atlantic to the Pacific Oceans was

not the same.

• NAVD88

In an effort to address these errors, the North American Vertical

Datum of 1988 (NAVD88) was realized from a single datum point in
Rimouski, Quebec. This datum is based on actual gravity, which

provides a better representation of true orthometric elevations. The
primary consideration in the choice of this datum point was to

minimize the recompilation of national mapping products. A side

effect of this choice is that the NAVD88 datum and the theoretical
level surface used to define GRS80 do not agree. The offset between

the NAVD88 vertical datum and the ITRF global geopotential model

is in the neighborhood of 0.27m

Survey Pro does not require choosing a specific vertical datum. For

RTK applications, elevations are solved relative to the base using the

vertical localization adjustment. Therefore, the vertical datum is
established by the datum of the base elevation.

Milbert D.G. Converting GPS Height into NAVD88 Elevation with

the GEOID96 Geoid Height Model

http://www.ngs.noaa.gov/PUBS_LIB/gislis96.html

p. 4