Glossary of Terms
2D Lock/Location - the GPS receiver has
fixed the current latitude and longitude - no
elevation. A minimum of three visible satellites are
3D Lock/Location - the GPS receiver has fixed
the current latitude, longitude and elevation. A
minimum of four visible satellites are required.
Almanac - all GPS satellites transmit
almanac data, which describes their orbits and states.
GPS receivers store this data to speed up
Azimuth - an azimuth is also
referred to as a bearing. It is the horizontal
direction from one point to another, measured in
Beacon - differential GPS uses stationary
beacons to transmit differential correction data to
nearby beacon receivers.
Cold Start -
when a GPS receiver downloads
almanac data from satellites and then uses it to
establish a fix.
a mathematical model which
describes a portion of the Earth's surface.
Geosynchronous Orbit -
an orbit where a
satellite rotates around the Earth at the same
rotational speed as the Earth.
a region of the Earth's
atmosphere between 40 and 500 kilometers high that
interferes with the transmission of GPS signals.
the angular distance of a location
north or south of the equator,
the angular distance of a
position east or west of the prime meridian (which
runs through Greenwich, England between the two poles)
Multiplexing Receiver -
a receiver which has
to switch between each satellite signal it is
tracking. Now essentially obsolete.
NAVigation Satellite Timing and
Ranging - official name for the global positioning
NMEA Standard - A National Marine Electronics
Association standard that defines the communication
protocols between marine instrumentation.
Parallel Channel Receiver - a receiver which
is able to simultaneously track multiple satellites,
instead of switching between signals.
Pseudo-random Code - the identifying signal
unique to each GPS satellite.
Selective Availability - the US Government
program which intentionally degraded GPS accuracy for
civilian receivers. Currently off.