gps-glossary-g

A specifically oriented reference ellipsoid. Typically, eight parameters are required to define a geodetic datum: two to specify the dimensions of the ellipsoid, three to specify the location of its center with respect to the earth's center of mass, and three to specify the orientation of the ellipsoid with respect to the average spin axis of the earth and the Greenwich reference meridian

Geodetic Height

The height of a point above an ellipsoidal reference surface. Also known as ellipsoidal height. The difference between the geodetic height of a point and its orthometric height is equal to the geoidal height

Geodetic surveys

Global surveys done to establish control networks as a basis for accurate land mapping

Geodetic.

Geographic, or pertaining to geodesy. Latitude and longitude readings are geodetic coordinates

Geographic Information System (GIS)

A computer based system that is capable of collecting, managing and analyzing geographic spatial data

Geoid

The undulating, but smooth, equipotential surface (a surface of equal gravity potential) of the earth's gravity field, which coincides most closely with mean sea level. The geoid is the primary reference surface for heights

Geometric Dilution of Precision (GDOP)

The effects of the combined errors of four variables (latitude, longitude, altitude, and time) on the accuracy of a three-dimensional fix

Geostationary Satellites

Those satellites situated in a constant orbit position relative to a given area of the globe with the purpose of maintaining constant coverage of that area

Getting

Ivan A. Getting, Father of the GPS system born 1912

GIS

Geographic Information System. A computer based system that is capable of collecting, managing and analyzing geographic spatial data

GLL

A data sentence that is part of the NMEA protocol for transferring information between electronic devices. The GLL sentence contains position information

Global Navigation Satellite System (GLONASS)

The Russian satellite navigation system. GLONASS provides worldwide coverage, however, its accuracy performance os optimized for the northern latitudes

Global Positioning System (GPS)

A global navigation system that is based on triangulation from a constellation of 24 satellites orbiting the earth. A GPS receiver pinpoints its position on earth by measuring its distance from the satellites. It does so by calculating the time it takes for a coded radio message to pass from the satellite to the GPS unit. A GPS unit needs at least three measurements to determine its exact position

GMT

Greenwich Mean Time or UT1 (Universal Time One) is a time scale tied to the rotation of the Earth in respect to the fictitious 'mean Sun'. UTC is, however, kept within 0.9 seconds of UT1, by virtue of leap seconds

GPS

Global Positioning System. Usually refers to the USA's NAVSTAR system.

GPS System Time

The time scale to which GPS signals are referenced. GPS Time derives from a composite or paper clock consisting of all operational monitor station and satellite atomic clocks. It is steered over the long run to keep it within about 1 micro-second of UTC, as maintained by the Master Clock at the U.S. Naval Observatory, ignoring the UTC leap seconds seconds

GPS week

Incremental number of weeks, starting at 0 hour UTC on the date January 6, 1980. April 6, 1997 is the first day of GPS week 900

Gravity void

A block or area of blocks within the gravity measurement database without observations. A geoid model relying upon this database would be weak and possibly in error at these blocks

Great Circle

The intersection of a plane through the center of the Earth and the surface of the Earth. The shortest distance between two points on the Earth is a great circle route. All longitudes are great circles. The only latitude that is a great circle is the Equator

Grid

A coordinate system that projects the earth on a flat surface, using square zones for position measurements.

Ground plane

A large flat metal surface, or electrically charged field, surrounding a GPS antenna used to deflect errant signals reflected from the ground and other near

Ground Speed

The velocity you are traveling relative to a ground position

Ground Wave.

A radiowave that travels along the earth's surface

GRS 80

The reference ellipsoid of the NAD83 coordinate system

Ground Speed