4 GPS system
Software uses the GPS navigation system to accurately determine your position and display it on the digital map.
4.1 Introduction to GPS
Automatic navigation in Software utilizes the Global Positioning System, made
available for civilian use by the U.S. Department of Defense. A GPS receiver calculates
its position by measuring the distance between itself and several (out of 24 operating)
visible satellites of the Navstar network.
The more satellites the receiver can detect, the more accurate the calculations will be.
Usually, as much as 4 to 6 satellites are visible (the maximum number is 12). The
minimal number of satellites required to determine the receiver's position is three.
Conditions for GPS reception
In ideal conditions, a typical GPS receiver used with Software can calculate its position
exact to a few metres. However, the GPS signal may be absorbed by building walls,
thick tree crowns, metal shieldings, or metalized and heated car windows. Covering
the receiver with a hand or a newspaper may also, to a lesser extent, weaken the
signal. The quality of GPS signal depends on the state of atmosphere, both its upper
(e.g. ionosphere) and the lower layer that influences the weather conditions. Sometimes, on cloudy and humid days the
GPS receiver may have problems with calculating its position. Another frequent problem related to problems with GPS
reading is incorrect cabling or close proximity to electronic devices that generate interference, and in particular to devices
used to monitor vehicle movement.
The accuracy of calculating the GPS position is greater, if the GPS receiver antenna is not covered, preferably in the open,
where the signal is not absorbed by buildings or thick foliage.
Extrapolate position
Software is adapted for city navigation and as such is equipped with solutions improving GPS reading by extrapolating the
vehicle's position based on the analysis of its direction and speed. However, the map can show a position outside the
route, e.g. when taking a fast turn. The "Extrapolate position" function can be turned on/off by selecting the setting you
want in "GPS - Settings" in the main menu. In this option you can also manually specify the time when Software
extrapolates/overtakes the GPS position obtained from the GPS receiver. This time depends on CPU speed, display rate
and palmtop memory.
4.2 Fixing GPS position
If, after turning on the GPS receiver, the "Searching for GPS signal" is played, and after a dozen or so minutes the correct
position is not found, that means the following:
• receiver has been detected by Software , but it relays information in non-supported protocol (other than NMEA
0183), or
• automatic COM port detection failed, or
• GPS signal is interfered with resulting in a failure of the GPS receiver to calculate the current position (e.g. user
remains indoors).
It should be noted that the so-called cold start (i.e. start after long non-use) or the first start of the GPS receiver may, in
case of certain models, take as much as dozen minutes or more. Before starting the troubleshooting, you should wait a
while longer.
After calculating the GPS position, Software automatically switches to the GPS tracking mode where the current position is
always displayed on the map.
The current position is indicated on the map as a pulsating circle with a direction arrow inside.
4.3 GPS receiver connection
GPS receiver - requirements
Software is supported by GPS receivers with COM interface (i.e. serial port for connecting to PCs), which relay their
position in the GPS NMEA 0183 protocol.
Connection types
The GPS receiver can be connected to a handheld computer in several ways, depending on the computer and receiver
equipment and accessories, e.g. with a cable, through a Compact Flash terminal or through a Bluetooth radio modem.
