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GPS & Navigation Terms:
Acquisition Time: The length of time that a GPS receiver typically takes to determine a position
from at least three satellites. Humminbird® GPS receivers provide very fast acquisition times
(under one minute), permitting users to get out on the water faster.
Alarm, Arrival: The audible alert that sounds when the boat is equal to or less than the alarm
setting (25 feet–3000 feet) from the location of the destination waypoint.
Alarm, Drift: Drift Alarm is an audible alert that sounds when the boat is equal to or over the alarm
setting (25 feet–3000 feet) from the location where the alarm was turned on.
Alarm, Off-Course: Off-Course Alarm is an audible alert that sounds when the boat’s distance from
the intended Track, (Cross Track Error), is equal to or over the alarm setting (25 feet – 3000 feet).
See Track and Cross Track Error.
Altitude: Altitude measures height above sea level. Altitude is a measurement that can be
provided by GPS.
Bearing (BRG): Bearing is the direction to a destination waypoint measured in degrees from
North (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is West).
Chartplotter: Chartplotter describes a navigation device that shows Present Position on a Map,
along with Tracks, Waypoints, and Routes. All Chartplotters are also considered Trackplotters. All
Humminbird® GPS Combo units are Chartplotters. See Trackplotter.
Cold Start: Cold Start refers to the procedure that a GPS receiver must perform when it does not
have historical information regarding its current location. This procedure typically lasts for several
minutes, and may be experienced upon first power up of the receiver, or if the receiver has been
moved a great distance.
Course Over Ground (COG): Course Over Ground is the current direction the boat is traveling
measured in degrees from North (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is
West). When the Course Over Ground is equal to Bearing, the boat is said to be “On Course” and
will arrive at the destination in the most efficient manner. COG is often confused with Heading.
See Heading.
Cross Track Error (XTE): Cross Track Error is the straight-line distance of the boat from the
intended Track. XTE measures how far the boat is off course, and also triggers the Off Course
Alarm. See Track.
Differential GPS (DGPS): Differential GPS is a system to improve the position accuracy of the
Department of Defense GPS through the use of secondary “correction signals” broadcast from
ground stations around the coastal United States and on some inland waterways. These
correction signals are provided by the USCG and received by an auxiliary Differential Beacon
Receiver (DBR) that connects to the GPS receiver. The advent of WAAS has largely negated the
need for the added expense of a DBR in the United States.
Distance To Go: Distance To Go is the straight-line distance between Present Position and the
Destination Waypoint. DTG and SOG (Speed Over Ground) are used to calculate Time To Go. See
Time to Go and Speed Over Ground.
Estimated Position Error (EPE): Estimated Position Error is a calculation that indicates the potential
position inaccuracy the user may experience due to a variety of GPS factors which include satellite
position in the sky, signal strength and others factors.
Fix Type: Fix Type indicates whether the GPS receiver is providing 2D fix or 3D fix. A 2D fix requires
only three satellites and provides only latitude and longitude. A 3D fix requires four or more
satellites, and provides latitude, longitude and altitude.
GPS: GPS is an acronym for Global Positioning System. GPS provides accurate position (latitude,
longitude, altitude) information virtually anywhere on the earth through satellite technology and
personal receivers on the ground. A series of geosynchronous satellites broadcast a unique signal
toward the earth once per second. A GPS receiver, such as that included with many Humminbird®
products, receives the signals from these satellites and is able to determine position based on very
slight differences in the time each signal is received and the receiver’s knowledge of the location
of each of the satellites.
Heading: Heading describes the direction the boat is pointing and is measured in degrees (i.e.
321°, where 000° is North, 090° East, 180° is South, 270° is West). Due to wind and waves, the boat
is often traveling in a slightly different direction than it is heading, and therefore Heading is often
confused with Course Over Ground. See Course Over Ground.
Map Datum: A Map Datum refers to a particular survey of the earth’s surface that was referenced
when creating a chart (i.e. WGS84). Since the earth is not flat, and not even consistently round, a
mathematical model must be used to translate coordinates from the sphere of the earth to the
flat surface of a chart. This mathematical model is the Map Datum. Historically, many different
Map Datums have been used around the world to create maps; often a reference to the Map
Datum can be found in the legend of a paper map. It is important to select the correct Map Datum
setting in your fishfinder when comparing GPS position to a paper chart to avoid slight position
inaccuracies. Almost all electronic charts use the WGS84 Map Datum and therefore, they do not
require setting changes.
MMC: MMC is an acronym for Multi Media Card. An MMC is a postage stamp-sized memory
device used to store electronic data such a maps, waypoints, routes and other information. MMC
is a very rugged format suitable for the marine environment, but it is not waterproof. The MMC is
removable from Humminbird® products, and can be used in a PC that is equipped with an
appropriate card reader. MMC is the same format that many digital cameras use. See SD.
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