Data Hacking

318 Glossary
Coordinates A unique numeric or alphanumeric scheme used to describe a precise location.
Course over ground The direction in which the GPS receiver is traveling.
Course to steer The direction to take in order to return on course.
Crosstrack Error The distance you are off a desired course in either direction.
CTS See Course to steer.
Cutoff angle See Mask angle.
Datum A position for which an accurate measurement of latitude and longitude is known. This is used
in map-making and in GPS for determining coordinates across the whole map. It is used in mapping and
surveying to ensure map accuracy.
DOP Dilution of Precision. An estimate made by the GPS of how much error exists in the reading.
Ephemeris The predictions of current satellite positions that are transmitted to the GPS receiver.
External antenna An antenna designed to be attached and detached from a GPS receiver.
Fix A single position that includes latitude, longitude, altitude, time, and date.
GLONASS This is the Russian counterpart to GPS.
GPS Global Positioning System.
GPSr Another term for a GPS receiver.
Healthy A term used to describe an orbiting GPS satellite suitable for use. “State” can also be used to
refer to satellite health.
Latitude A north-south measurement of position perpendicular to the Earth’s polar axis.
Longitude An east-west measurement of position. This is measured in relation to the prime meridian
(the line corresponding to 0 o longitude), an imaginary circle that passes through both the north and south
poles.
Magnetic north The direction in which the north end of the compass needle points.
Mask angle The minimum elevation of a satellite above the horizon to ensure a good signal. This can be
between 5 degrees and 15 degrees. GPS receivers usually ignore satellites below this elevation.
Multipath error Error caused by the interference of a GPS signal. It occurs when a signal from one
satellite has reached the receiver antenna more than once because it has taken two or more different paths.
It is generally caused when one signal has been bounced or reflected.
P-code Short for “Precision,” a name given to the encrypted military GPS signal.
Position The latitude, longitude, and altitude of a particular point. Often, an estimate of error is associated
with a position.
SA See Selective availability.
Satellite constellation The arrangement of the GPS satellites at any particular time.