Trimble Outdoors Part Number 45005-00-ENG, AcutimeTM2000 Synchronization Kit manual Gdop

Glossary

GDOP	Geometric Dilution of Precision. GDOP describes how
	much an uncertainty in pseudo-range and time affects the
	uncertainty in a position solution. GDOP depends on where
	the satellites are relative to the GPS receiver and on GPS
	clock offsets.
geodetic datum	A mathematical model designed to best fit part or all of the
	geoid. It is defined by an ellipsoid and the relationship
	between the ellipsoid and a point on the topographic surface
	established as the origin of datum. This relationship can be
	defined by six quantities, generally (but not necessarily) the
	geodetic latitude, longitude, and the height of the origin, the
	two components of the deflection of the vertical at the
	origin, and the geodetic azimuth of a line from the origin to
	some other point. The GPS uses WGS-84.
geoid	The actual physical shape of the earth which is hard to
	describe mathematically because of the local surface
	irregularities and sea-land variations. In geodetic terms it is
	the particular equipotential surface which coincides with
	mean sea level, and which may be imagined to extend
	through the continents. This surface is everywhere
	perpendicular to the force of gravity.
GPD	GPS with differential corrections applied.

Glossary-6 Acutime 2000 Synchronization Kit User Guide