Humminbird 998c SI - Manual (Page 157)

Glossary GPS & Navigation Terms
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advent of WAAS has largely negated the need for the added expense of a DBR in the
United States.
Distance To Go 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) 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 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 (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. See
How GPS Works .
Heading 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 Refers to a particular survey of the earth’s surface that was referenced
when creating a chart (i.e. WGS84). 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 (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.
MMC is the same format that many digital cameras use. See
SD .
North, Magnetic The principle reference point of the compass (i.e. North is 000°).
Magnetic North relies on the earth’s magnetic field to align a metal pointer generally
towards True North. However, due to local variations in the earth’s magnetic field
around the globe, the difference between True North and Magnetic North can be
greater than 10°. See
True North .
North, True The principle reference point of the compass (i.e. North is 000°). True
North uses the axis of the rotation of the earth as the reference for North and is
constant for all points on the earth. Most GPS units default to True North as the
setting. The GPS heading may vary from the boat compass heading because the
compass uses Magnetic North. See
Magnetic North .
Present Position The current location (latitude, longitude) determined by GPS. The
Present Position is indicated on-screen by a directional boat icon if the boat is moving
or a round symbol if the boat is stationary.
Route A series of waypoints linked together in a specific sequence to define a
navigation path between two points, and saved in the fishfinder’s memory. Routes are
often used when frequently traveling between two or more locations because it is a
faster and more accurate method than repeatedly selecting individual waypoints each
time one travels through the same area. Routes consist of a Start Waypoint, an End
Waypoint, and a series of waypoints in between. Users can begin navigation at the
beginning, the end (to run the route in reverse) or at any waypoint in between. See
Waypoint .
SD (Secure Digital) An SD card is virtually identical in function to an MMC;
however, the speed at which information can be accessed is generally faster, the
storage capacity is generally larger, and the card has security features which can be
used to prevent extracting the data from the card. SD is the same format that many
digital cameras use. See MMC.
Glossary - GPS & Navigation Terms