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| GDOP |
General dilution of precision. The relationship between errors
in receiver position, time and receiver to satellite range.
This is sometimes mis-called Geometric DOP. GDOP2 = PDOP2 +
TDOP2 See also: Dilution of Precision |
| Geocentre |
The centre of the Earth. |
| Geodesy |
The science related to the determination of the size and
shape of the Earth (geoid) by direct measurements. |
| Geodetic Datum |
A mathematical model designed to best fit part or all of
the geoid. GPS uses WGS 84. A model is defined by an ellipsoid
together with the relationship between the ellipsoid and a point
on the topographic surface established as the origin of datum.
This relationship can be defined by several quantities, one
method is to define 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. Another is to define differences
with respect to WGS 84 in the position of its centre (dy,dy,dz),
its rotations (ex,ey,ez) and any error in scale. |
| Geodetic surveys |
Global surveys done to establish control networks (comprised
of reference or control points) as a basis for accurate land
mapping. |
| Geoid |
The particular equipotential surface that coincides with
mean sea level and that may be imagined to extend through the
continents. This surface is everywhere perpendicular to the
force of gravity. |
| Geoid Height |
The height above the geoid is often called elevation above
mean sea level. |
| GGA |
An NMEA sentence in latitude, longitude, and altitude |
| GLL |
An NMEA sentence in latitude and longitude. |
| Global Navigation Satellite System (GLONASS) |
This is the Russian counterpart to GPS. GLONASS provides
worldwide coverage, however, its accuracy performance is optimized
for the northern latitudes. and is specificed as identical to
that of GPS SPS. |
| GNSS - Global Navigation
Satellite System |
Organizing concept of a European system that would incorporate
GPS, GLONASS, and other space-based and ground-based segments
to support all forms of navigation. |
| GPS |
The U.S. Department of Defense Global Positioning System:
A constellation of 24 satellites orbiting the earth at a very
high altitude. GPS satellites transmit signals that allow one
to determine, with great accuracy, the locations of GPS receivers.
The receivers can be fixed on the Earth, in moving vehicles,
aircraft, or in low-Earth orbiting satellites. GPS is used in
air, land and sea navigation, mapping, surveying and other applications
where precise positioning is necessary.
The space segment (24 NAVSTAR satellites in six different
orbits)
The control segment (five monitor stations, one master control
station, and three upload stations).
The user segment (GPS receivers).
NAVSTAR satellites carry extremely accurate atomic clocks
and broadcast coherent simultaneous signals.
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| GPS ICD 200 |
The GPS interface Control Document is a government document
that contains the full technical description of the interface
between the satellites and the user. GPS receivers must comply
with this specification if they are to receive and process GPS
signals properly. |
| GPSIC |
GPS Information Center (USCG) |
| Greenwich Mean Time (GMT) |
See universal time.
This is a few seconds different to GPS time. GMT and Universal
time are often used interchangeably. |
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