Lowrance electronic Lowrance GlobalMap 7200C - Manual (Page 14)

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Remember, the unit must have a clear view of the satellites in order to
receive their signals. Unlike radio or television signals, GPS works at
very high frequencies. These signals can be easily blocked by trees,
buildings, an automobile roof, even your body.
Like most GPS receivers, this unit doesn’t have a compass or any other
navigation aid built inside. It relies solely on the signals from the satel-
lites to calculate a position. Speed, direction of travel, and distance are
all calculated from position information. Therefore, in order for the
GlobalMap to determine direction of travel, you must be moving and
the faster, the better. This is not to say that it won’t work at walking or
trolling speeds — it will. There will simply be more "wandering" of the
data shown on the display.
GPS is plenty accurate for route navigation, but the U.S. Federal Avia-
tion Administration has special needs for aircraft traffic control that go
beyond basic GPS. The FAA has a program to boost GPS performance
even further with its Wide Area Augmentation System, or WAAS. This
GPS add-on will include a time control element that will help airliners
fly closer together while avoiding collisions. In addition to carefully
spacing airplanes along travel corridors, WAAS will eventually make
instrument landings and takeoffs more accurate as it replaces existing
aviation navigation systems.
Non-aviators can use WAAS signals to make their GPS navigation even
more accurate. Your unit receives both GPS and WAAS signals. How-
ever, WAAS has some limits you should know about.
WAAS can boost the accuracy of land GPS navigation, but the system
is designed for aircraft. The satellites are in a fixed orbit around the
Equator, so they appear very low in the sky to someone on the ground
in North America. Aircraft and vessels on open water can get consis-
tently good WAAS reception, but terrain, foliage or even large man-made
structures frequently block the WAAS signal from ground receivers.
You'll find that using your GPS receiver is both easy and amazingly
accurate. It’s easily the most accurate method of electronic navigation
available to the general public today. Remember, however, that this
receiver is only a tool. Always have another method of navigation avail-
able, such as a map or chart and a compass.
Also remember that this unit will always show navigation information
in the shortest line from your present position to a waypoint, regardless
of terrain! It only calculates position, it can’t know what’s between you
and your destination, for example. It’s up to you to safely navigate
around obstacles, no matter how you’re using this product.