K GPS Glossary of Terms
MiLLennium GPSCard SW Version 4.503/4.52 Command Descriptions Manual Rev 2 273
Root Mean Square A probability level of 68%.
(RMS)
Route A planned course of travel, usually composed of more than one navigation leg.
RT-20 NovAtel’s Double Differencing Technology for real-time kinematic (RTK) carrier phase
floating ambiguity resolution.
Radio Technical An organization which developed and defined a message format for
Commission for differential positioning. See Appendix F Standards and References on Page 239 for
Aeronautics further information.
(RTCA)
Radio Technical An organization which developed and defined the SC-104 message format
Commission for for differential positioning. See Appendix F Standards and References on Page 239 for
Maritime Services further information.
(RTCM)
Real-Time A type of differential positioning based on observations of carrier phase. In
Kinematic (RTK) this document it is also used with reference to RT-2 and RT-20.
Selected Waypoint The waypoint currently selected to be the point toward which the vessel is travelling.
Also called "to" waypoint, destination or destination waypoint.
Selective The method used by the United States Department of Defence to control
Availability (SA) access to the full accuracy achievable by civilian GPS equipment (generally by
introducing timing and ephemeris errors).
Sequential Receiver A GPS receiver in which the number of satellite signals to be tracked exceeds the number
of available hardware channels. Sequential receivers periodically reassign hardware
channels to particular satellite signals in a predetermined sequence.
Spherical Error The radius of a sphere, centred at the user’s true location, that contains 50
Probable (SEP) percent of the individual three-dimensional position measurements made using a
particular navigation system.
Spheroid Sometimes known as ellipsoid; a perfect mathematical figure which very closely
approximates the geoid. Used as a surface of reference for geodetic surveys.
Standard A positioning service made available by the United States Department of
Positioning Defence which is available to all GPS civilian users on a continuous,
Service (SPS) worldwide basis (typically using C/A Code).
Space Vehicle ID Sometimes used as SVID. A unique number assigned to each satellite for
(SV) identification purposes. The ‘space vehicle’ is a GPS satellite.
TDOP Time Dilution of Precision [See DOP]
Three-Dimensional The number of hours-per-day when four or more satellites are available with
Coverage acceptable positioning geometry. Four visible satellites are required to determine
location and altitude.
Three-Dimensional Navigation mode in which altitude and horizontal position are determined
(3D) Navigation from satellite range measurements.
Time-To-First-Fix The actual time required by a GPS receiver to achieve a position solution.
(TTFF) This specification will vary with the operating state of the receiver, the length of time
since the last position fix, the location of the last fix, and the specific receiver design.
Track A planned or intended horizontal path of travel with respect to the Earth rather than the
air or water. The track is expressed in degrees from 000° clockwise through 360° (true,
magnetic, or grid).
Track Made Good The single resultant direction from a point of departure to a point of arrival or subsequent
position at any given time; may be considered synonymous with Course Made Good.