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Glossary GPS & Navigation Terms
148
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 calculated using 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 Points that can be saved before
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 between when points are saved, and thus extend the distance covered by a track.
Trackscan alsobe permanently saved to memory and re-displayed at theuser’s option.
Track Line (TRK) The planned line of travel between two waypoints, and it
represents the most efficient path between the two points because it is a straight line.
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 reference grid 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 Time Constant) UTCis the “standard time”usedin navigationand
is the local time in Greenwich England. (UTC is equivalent to Greenwich Mean Time
(GMT)).
WAAS (Wide Area Augmentation System) WAASis 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 coalitions have 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
toname and assigna symbol to the saved location.Depth, Date, andTime ofDaywhen
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 relative to
a waypoint,and is useful for fishing oversubmerged structure.With Waypoint Targets,
a quick look at the screen lets you know how far off the waypoint the boat has drifted.
Glossary - GPS & Navigation Terms