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K GPS Glossary of Terms
270 MiLLennium GPSCard SW Version 4.503/4.52 Command Descriptions Manual Rev 2
Ambiguity constant.
Estimates
Flash ROM Programmable read-only memory.
Floating Ambiguity Ambiguity estimates which are not held to a constant value, but are allowed
Estimates to gradually converge to the correct solution.
Geometric Dilution [See DOP]
of Precision (GDOP)
Geoid The shape of the earth if it were considered as a sea level surface extended continuously
through the continents. The geoid is an equipotential surface coincident with mean sea
level to which at every point the plumb line (direction in which gravity acts) is
perpendicular. The geoid, affected by local gravity disturbances, has an irregular shape.
Geodetic Datum The reference ellipsoid surface that defines the coordinate system.
Geostationary A satellite orbit along the equator that results in a constant fixed position over a
particular reference point on the earth’s surface. (GPS satellites are not geostationary.)
Global Positioning Full name is NAVSTAR Global Positioning System. A space-based radio
System (GPS) Positioning system which provides suitably equipped users with accurate position,
velocity and time data. GPS provides this data free of direct user charge worldwide,
continuously, and under all weather conditions. The GPS constellation consists of 24
orbiting satellites, four equally spaced around each of six different orbital planes. The
system is being developed by the Department of Defence under U.S. Air Force
management.
Great Circle The shortest distance between any two points along the surface of a sphere or ellipsoid,
and therefore the shortest navigation distance between any two points on the Earth. Also
called Geodesic Line.
Handshaking Predetermined hardware or software activity designed to establish or maintain two
machines or programs in synchronization. Handshaking concerns the exchange of
messages or packets of data between two systems with limited buffers. Hardware
handshaking uses voltage levels or pulses in wires to carry the handshaking signals.
Software handshaking uses data units (e.g. ASCII characters) carried by some
underlying communication medium.
Horizontal Dilution [See DOP]
of Precision (HDOP)
Horizontal and Time [See DOP]
Dilution of Precision
(HTDOP)
Heading The direction in which a vessel points or heads at any instant, expressed in degrees 000°
clockwise through 360° and may be referenced to True North, Magnetic North, or Grid
North. The heading of a vessel is also called the ship's head. Heading is a constantly
changing value as the vessel oscillates or yaws across the course due to the effects of the
air or sea, cross currents, and steering errors.
Integer Ambiguity Carrier phase ambiguity estimates which are only allowed to take on integer
Estimates values.
Iono-Free Carrier A linear combination of L1 and L2 carrier phase measurements which
Phase Observation provides an estimate of the carrier phase observation on one frequency with the effects
of the ionosphere removed. It provides a different ambiguity value (non-integer) than a
simple measurement on that frequency.
Kinematic The user’s GPS antenna is moving. In GPS, this term is typically used with precise
carrier phase positioning, and the term dynamic is used with pseudorange positioning.