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Using a GPS
What is GPS?
The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or set-up charges to use GPS.
How it works? GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information back to earth.
GPS services take this information and use triangulation to calculate the user’s exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the
satellite is. Now, with distance
measurements from a few more satellites, the receiver can determine the user’s position and display it on the unit’s electronic map.
A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user’s 3D position (latitude, longitude and
altitude). Once the user’s position has been determined, the GPS receiver can calculate other information such as speed, trip distance, distance to destination,
sunrise and sunset time and more. Today’s OPS receivers are extremely accurate. Although certain atmospheric factors and other sources of error can affect their accuracy, most receivers are accurate to within 10—15 metres. Both hand-held models and models designed to be fitted in vehicles are available on the market.
GPS satellites transmit two low-power radio signals, which travel by line of sight, which means they’ll pass through cloud, glass and plastic but will not go through most solid objects in the vicinity, such as buildings and mountains. Most GPS receivers can display positions in various position formats. The format used in this book is to present latitude and longitude in degrees, minutes and thousandths of a minute (hddd°mm.mmm’), the default format in Garmin OPS receivers. Make sure these co-ordinates match those on your own OPS receiver and maps.
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