User's manual BLUE Edition
6 Glossary
A COM port is a connector to a communications interface, usually | |
| the serial port. The ports are numbered by a number behind |
| “COM”. A communications interface is designed to connect |
| hardware like a mouse or a GPS receiver. |
GMT | GMT (Greenwich Mean Time) is the mean solar time at the Royal |
| Greenwich Observatory in Greenwich near London, England, |
| which by convention is at 0 degrees geographic longitude. |
| Theoretically, noon Greenwich Mean Time is the moment when |
| the Sun crosses the Greenwich meridian (and reaches its highest |
| point in the sky in Greenwich). Up to 1972, GMT was the global |
| time standard. Because of the Earth's uneven speed in its elliptic |
| orbit, GMT has been replaced by UTC (Universal Time |
| Coordinated) which is an ultra stable time standard based on |
| atomic clocks. |
GPS | The GPS (Global Positioning System) is based on 24 satellites, |
| which are in orbit round the earth. They are permanently |
| emitting the time and their current position. The GPS receiver |
| receives this information and calculates the longitude and the |
| latitude of its own current position. |
| The signals of at least three satellites are needed to determine |
| the longitude and the latitude. With the signals of at least four |
| satellites the elevation may be calculated, too. The determination |
| has an accuracy of about 3 yards. |
HDOP | The Horizontal Dilution of Precision (HDOP) indicates the quality |
| of position determination. Theoretically any value from 0 to 50 is |
| possible. The smaller the value is, the more accurate is the |
| position determination (value 0 = no deviation from the actual |
| position). Values up to 8 are convenient for street navigation. |
POI | Point of Interest (POI). See Special destination. |
Special destination | Special destinations, also called POI (Points of Interest), are |
| covered by the map and may be displayed on it. Harbours, |
| airports, restaurants, hotels, petrol stations, public buildings, and |
| others belong to the special destinations. You may determine |
| special destinations as itinerary points for navigation purposes. |
Glossary | - 71 - |
