Glossary

Active Leg: The segment of a route currently being traveled.

Altitude: The current elevation above sea level.

BRG Bearing: The compass direction from your position to a destination, measured to the nearest degree.

Buoy: A navigation aid (usually found in marine charts) that is floating in water. The position can vary due to the magnitude and direction of the current.

COG Course Over Ground: The direction the receiver is moving. COG can be reported in true or magnetic north values.

Coordinates: A unique numeric or alphanumeric description of the position.

CTS Course to Steer: The direction you should be traveling in order to return to the course while proceeding towards the destination. It is a "compromise" course bearing that projects from your current position to a point on the courseline midway between a point perpendicular to your position and the current leg destination waypoint.

Data Links: Data links are Differential Global Positioning System (DGPS) radio signals transmitted from a reference station or relay antenna at a known location to one or more rover receivers, to provide the positioning correction data that gives Thales Navigation GPS systems maximum accuracy, up to within a centimeter. Data links allow reference stations, relay transmitters and rover receivers to communicate calculations performed at each location to build a preponderance of data that is cross-checked at every point for verified precision. These data links are critical to collecting reliable GPS data. Thales Navigation has developed data link solutions for optimum system integration, and hardware and software compatibility with the highest market standards, to ensure superior performance and absolute reliability. A number of factors including range, update rate and error correction rate determine the quality and specific application of a data link. Thales Navigation has developed data link solutions that are readily adaptable to any application, overcoming the limitations to accuracy associated with vehicle tracking, DGPS, Local Area Differential GPS (LADGPS) and general data transfer. There are three types of data links deployed in Thales Navigation GPS systems for high-performance accuracy:

1) HF data link operates in the HF frequency between 1.6 MHz and 3.5 MHz. Primarily designed for LADGPS marine applications, HF data link is optimized for a meter-accurate update rate and easy government frequency allocation. Using a BCPSK modulation, advanced data compression, and high-performance GPS signal correction algorithms, HF data link offers superior accuracy for marine applications. With an operating range of 100 to 800 kilometer, HF data link is integrated into a number of Ashtech Marine Survey & Navigation GPS solutions.

2) UHF data link operates in the UHF frequency between 410 MHz and 470 MHz. Optimized for LADGPS or Real-Time Kinematic (RTK) marine and land survey applications, UHF data link is available in a number of configurations for maximum performance according to the requirements of specific Thales Navigation GPS systems. UHF data link can be configured with a DQPSK modulation, operating at 1200 baud. This configuration is compatible with earlier DGPS and Kinematic Applications in Real Time (KART) applications and uses NDS100MkII signal format. When configured with a GMSK modulation and Long Range Kinematic (LRK) signal format, UHF data link is optimized for LRK or KART kinematic applications. A third option uses a common signal format known as RTCM. UHF data link has a range of 80 kilometers and is integrated into a number of Ashtech Marine Survey & Navigation and Land Survey GPS solutions.

3) UHF bi-directional data link also operates in the UHF range and offers additional flexibility in configuring data processing functionality. Based on the Time Division Multiple Access (TDMA) principle, UHF bi-directional data link uses an MSK modulation optimized for relative positioning systems, used in marine seismic exploration and fleet management. UHF bi-directional data link is integrated into a number of Ashtech Marine Survey & Navigation and Fleet Management GPS solutions.

Datum: Refers to the theoretical mathematical model of the earth’s sea level surface. Mapmakers may use a different model to chart their maps, so position coordinates will differ from one datum to another. The datum for the map you are using can be found in the legend of the map. If you are unsure of which datum to use, use WGS84.

Default: The value or setting automatically chosen by the unit unless otherwise directed. Can be changed in Setup.

DGPS (Differential Global Positioning System): A Differential Global Positioning System (DGPS) is a system designed to improve the accuracy of Global Navigation Satellite Systems (GNSS) by measuring infinitesimal changes in variables to provide satellite positioning corrections. Two or more receivers observe the same set of satellites, taking similar measurements that produce similar errors when positioned closely together. A reference receiver, placed at a known location, calculates its theoretical position and compares it to the measurements provided by the navigation satellite signals. The difference between the two values reveals the measurement error. The reference receiver then transmits a corrected signal to any number of receivers at unknown positions within the area covered by the DGPS. Accuracy of global satellite positioning is thereby increased from 15 meters to within a few meters. This technique compensates for errors in the satellite navigation system itself but may not always correct errors caused by the local environment when satellite navigation signals are reflected off of tall buildings or nearby mountains, creating multi-path signals. The accuracy of DGPS decreases with asynchronous measurement caused by spatial and temporal error decorrelation when the system receivers are set at greater distances apart.

DST Distance: Distance from position to destination.

ETA Estimated Time of Arrival: The estimated time of day the leg’s destination waypoint will be reached.

ETE Estimated Time Enroute: The estimated time remaining to reach the next waypoint in a route.

HDG Heading: The direction you are facing, defined as an angle from North.

Latitude: The angular distance north or south of the equator measured by lines encircling the earth parallel to the equator from 0° to 90°.

LAT/LON: Coordinate system using latitude and longitude coordinates to define a position on the earth.

Leg (Route): A segment of a route that has a starting (FROM) waypoint and a destination (TO) waypoint. A route may consist of 1 or more legs. A route that is from waypoint A to waypoint B to waypoint C to waypoint D has three legs with the first being from waypoint A to waypoint B.

Longitude: The angular distance east or west of the prime meridian (Greenwich Meridian) as measured by lines perpendicular to the parallels and converging at the poles from 0° to 180°.

Magnetic North: The direction relative to a magnetic compass.

NMEA National Marine Electronics Association: A professional organization that defines and maintains the standard serial format used by marine electronic navigation equipment and computer interfaces.

OSGB: A coordinate system describing only Great Britain, similar to UTMs. Used with GRB36 datum.

Position fix: Position coordinates as computed by the Meridian.

Satellite-Based Augmentation Systems (SBAS): Networks of ground relay stations and geostatic satellites designed to receive satellite navigation signals and transmit corrected time and distance measurements that greatly improve accuracy. Observation and relay stations have been set at known positions all over the world, while their geostatic satellites continuously maintain a fixed position above the Earth. Using these known values for distance, SBAS corrects satellite navigation signals for atmospheric delays, incorrect satellite positioning and poor geometry, sometimes caused by inline or close alignment of satellites, increasing accuracy in specific regions. SBAS is vital to providing the reliability and precision required by aviation and other precision-critical applications. (See WAAS)

SOG Speed Over Ground: The speed at which the receiver is moving.

TMP Temperature:

True North: The direction to North Pole from an observer’s position. The north direction on any geographical meridian.

UTC Universal Time Coordinated: Formerly referred to as Greenwich Mean Time (GMT).

UTM Universal Transverse Mercator: metric grid system used on most large and intermediate scale land topographic charts and maps.

VMG Velocity Made Good: The component of the velocity that is in the direction of the destination.

WAAS (Wide Area Augmentation System): In North America, WAAS provides satellite navigation correction and validation, making WAAS-enabled receivers at least five times more accurate than standard devices. WAAS relay stations have been set at known positions throughout North America. SBAS-enabled receivers do not require any additional equipment to use WAAS correction signals and, as with satellite navigation signals, there are no setup or subscription fees. WAAS is accurate to within three meters or less. System upgrades are being developed which will soon provide accuracy to well within one meter. In 2003, the FAA (Federal Aviation Administration) plans to certify WAAS for use in low-altitude maneuvering, instrument approach and other sensitive aviation applications.

WPT Waypoint: A location saved in the receiver’s memory which is obtained by entering data, editing data, calculating data or saving a current position. Used to create routes.

XTE Cross Track Error: The perpendicular distance between the present position and the courseline. Given as a distance, right or left, of course when facing the destination.

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