Lowrance electronic Lowrance GlobalMap 5200C User Manual

Page 13

A minimum of three satellites are required to determine a 2D fix.

The system requires signal reception from three satellites in order to

determine a position. This is called a 2D fix. It takes four satellites to

determine both position and elevation (your height above sea level —

also called altitude). This is called a 3D fix.
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 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 plan under way to boost GPS per-

formance even further with its Wide Area Augmentation System, or

WAAS.
This GPS add-on will include a time control element that will help air-

liners fly closer together while avoiding collisions. In addition to care-

fully spacing airplanes along travel corridors, WAAS will eventually

make instrument landings and takeoffs more accurate as it replaces

existing aviation navigation systems.