Humminbird HELIX 5 SI GPS Operation Manual page 178

Glossary GPS & Navigation
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
SD
environment, but it is not waterproof. MMC is the same format that many digital cameras use. See .
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
True North
North can be greater than 10°. See .
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
Magnetic North
compass uses Magnetic North. See .
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
Waypoint
in reverse) or at any waypoint in between. See .
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.
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
SOG DTG.
the SOG and DTG. See and
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. Tracks can also be permanently saved to memory and
re-displayed at the user's option.
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Glossary - GPS & Navigation