Definition
Global Positioning System (GPS) is a navigation system which gives information on location and time to its users in all weather conditions.
GPS operates through the continuous interaction of three distinct segments: the control segment, the space segment, and the user segment.
1. Control Segment
The control segment comprises a master control station, alternative master control station, command and control antennas, as well as monitor stations. Monitor stations receive signals from GPS satellites and send them to the master control station. The master control station generates navigation messages on Earth. Antennas on Earth transmit information to the GPS satellites, which includes:
- GPS satellite position
- Time correction factor for the GPS satellite clock
- Atmospheric data
- Almanac
2. Space Segment
The space segment consists of a network of GPS satellites orbiting the Earth. GPS satellites orbit at an orbital height of \(20\ 000\text{ km}\). The orbit is known as a semi-synchronous Earth orbit with an orbital period of about 12 hours. At least 4 GPS satellites can be seen at an angle of \(15^\circ\) or more from the horizontal axis at any time from all locations on Earth. Satellites transmit signals to GPS receiving devices containing the position of the GPS satellite and the time the signal is sent.
3. User Segment
A GPS user is anyone using a GPS receiving device, such as a smartphone or car GPS tracker. The device receives satellite signals to determine coordinates and time.
GPS Coordinate Formats
Coordinates of a location can be written in two formats:
Degrees, Minutes and Seconds (DMS)
Format displays degrees (\(^\circ\)), minutes (\('\)), and seconds (\("\)) along with hemisphere indicators (N/S for Latitude, E/W for Longitude). Directions 'East' and 'West' are based on the Greenwich Meridian.
Example: National Planetarium, Kuala Lumpur: \(3^\circ 08' 22.04''\text{N}\), \(101^\circ 41' 22.53''\text{E}\).
Decimal Degree (DD)
Format displays values in decimal numbers. For latitude, a positive value (\(+\)) represents the Northern Hemisphere, while a negative value (\(-\)) represents the Southern Hemisphere. For longitude, a positive value (\(+\)) represents east of the Greenwich Meridian, while a negative value (\(-\)) represents west of the Greenwich Meridian.
Example: National Planetarium, Kuala Lumpur: \(3.139456\), \(101.689593\).
Uses and Applications of GPS
GPS is used for navigational purposes in various modes of transport: land, sea, air, and space transport. Everyday navigation mobile applications include Google Maps and Waze. Devices include car GPS trackers and smartphones. Navigational apps provide notifications of road accidents and traffic conditions to road users. GPS activities are conducted in open spaces, such as school fields, rather than inside classrooms to prevent signal obstruction and ensure clear line-of-sight reception from satellites.
