Glossary | GPS & Navigation Terms |
Selective Availability (SA) A GPS system “feature” that can be implemented by the U.S. Department of Defense (DoD) to degrade the accuracy of GPS positioning information.With SA active,the GPS is accurate to within 100 meters 95% of the time. With SA inactive, the GPS is accurate to within 45 meters 95% of the time. Currently, SA is inactive and the consumer can enjoy the greater precision GPS provides; however,the DoD reserves the right to activate SA at any time.
Speed Over Ground (SOG) The measurement of the boat’s progress across a given distance and the speed measurement provided by GPS. An alternate, Speed Through Water, is provided by a speed paddlewheel, and is the measurement of the flow past the boat, which may vary depending on current speed and direction. Speed Over Ground is optimal for navigation because accurate destination times can be derived from this measurement. Humminbird® products allow for input and display of both speed measurements.
Time To Go (TTG) The estimated time required to reach the destination waypoint. TTG is calculatedusing the SOG and DTG. See SOG and DTG.
Track A series of saved points that define the past path of the boat. These Track Points are saved at regular time intervals. Tracks are a useful and quick method to see where you’ve been, and an easy guide to follow to get you back to the starting point. Generally, all GPS units have a limited number of Track Pointsthat can be savedbefore the unit runs out of memory and begins erasing the first track points saved. Because of this, the user can adjust the Track Point Interval menu to increase the amount of time betweenwhen points are saved, and thus extend the distancecovered by a track. Tracks can also be permanentlysaved to memory and
Track Line (TRK) The planned line of travel between two waypoints, and it represents the most efficientpath between the two points because it is a straightline. The TRK is measured in degrees (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is West). See Cross Track Error and Course Over Ground.
Trackplotter A navigation device that shows Present Position, along with Track, Waypoint, and Routes, but NO MAP in the background. See Chartplotter.
Trolling Grid A Humminbird® feature that displays a precise referencegrid around a waypoint. This grid is used as a guide pattern for trolling around a specific area to assure a more efficient and complete coverage of that area.
UTC (Universal TimeConstant) UTC is the “standard time” used in navigation and is the local time in Greenwich England. (UTC is equivalent to Greenwich Mean Time (GMT)).
WAAS (Wide Area AugmentationSystem) WAAS is complementary technology to GPS that provides enhanced accuracy through correction signals broadcast from Federal Aviation Administration WAAS satellites stationed over the USA. These secondary signals are automatically received by the standard Humminbird® GPS Receiver. With WAAS signal, GPS accuracy is improved to within 3 meters 95% of the time. Outside the United States, regional governmental coalitionshave created similar systems such as EGNOS (Europe) and MSAS (Japan).
Waypoint The saved location (latitude, longitude) of a point of interest that is stored in a GPS receiver’s memory. This can include a marker buoy, dock, fishing hole, or anywhere else the user may want to return to. Humminbird® products offer the ability to name and assign a symbol to the saved location. Depth, Date, and Timeof Day when the waypoint was created is also saved.
Waypoint Target A Humminbird® feature that displays a precise “bull’s eye” around a selected waypoint. This bull’s eye is used to easily monitor boat position relativeto a waypoint, and is useful for fishing over submerged structure.With WaypointTargets, a quick look at the screen lets you know how far off the waypoint the boat has drifted.
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