RightWay GPS Navigator RW 430 - Manual (Page 11)

11
ABOUT GPS NAVIGATION
The Global Positioning System (GPS) is a space-based radio-navigation system. This
system consists of 24 satellites, which orbit the Earth at an altitude of approximately
17,500 kilometers. Each of the 24 satellites is deployed in 6 orbital planes and circles the
earth twice a day. These systems of satellites continuously transmit signals containing
precise information, 24 hours a day in any weather condition, everywhere around the
world. By processing the signals received, the RW 430 GPS Navigator provides users
with helpful information of position, velocity, and time for navigation and location based
services anytime.
The time it takes the GPS to find the satellites is called the Time to First Fix (TTFF). The
GPS receiver needs to lock on to at least 3 satellites for a position fix. The RW 430 GPS
Navigator acquires a position fix typically within 10 seconds from a hot-start state and
roughly 80 seconds from a cold-start state. The initial state of the receiver, (i.e. the latest
status in the memory of the receiver) primarily determines the time of TTFF. If you have
not used your GPS unit for several months, the almanac data for the satellites may be
out of date. The unit is capable of recollecting this information on its own, but the process
can take as long as 3 to 5 minutes. The TTFF will also be longer the very first time the
user first turns on the GPS receiver, when a GPS receiver has lost memory, or has been
moved over 300 miles (500 km) from its last location will also be longer.
Both TTFF and positional accuracy can be affected by obstructions such as tall buildings,
narrow streets & passageways, protective film on glass, heavy foliage, large cliffs, and
other situations where GPS satellite signals are blocked. Once there is a position fix, the
RW 430 uses the satellite signals to calculate an exact geodetic location through
triangulation method, contained in 10 meters CEP accuracy devoid of Selective
Availability (SA). The position data is then converted within the receiver to latitude and
longitude coordinates, which is usually provided in the geodetic datum on which GPS is
based (WGS 84). The map datum selected on a GPS receiver needs to match the datum
listed on the corresponding paper map in order for the position readings to match. Using
the wrong datum can result in position offsets of hundreds of meters or much more. In
addition to using the wrong datum, accuracy can be limited by satellite orbiting errors,
multi-path signals, atmospheric delay and receiver clock timing.
Caution! The United States government operates the Global Positioning System (GPS)
and is solely responsible for its accuracy and maintenance. Changes by the
United States government may affect the accuracy and performance of all
GPS equipment, including your personal navigation device.
Caution! Ordinances or laws may restrict use of certain abilities of your navigation
device on public or private land.