GPS Global Positioning Systems

Titanic – Hit an iceberg and sunk - April 14, 1912 Discovered – Sept. 1, 1985 by Dr. Robert Ballard at a depth of 4 km.

Ever been LOST?

Airlines

Boating

Automobiles The maps in the background are from another computer application called a GIS (Geographic Information Systems)

Military

Google Earth

Cell Phones and GPS Tracking

Why would farmers use GPS? Why would golfers use GPS? Why would hikers or mountain bikers use GPS? Why would hospitals and ambulances use GPS? Why would robots use GPS? The list goes on…..

- GPS is a navigation system - GPS is a navigation system - Satellites orbiting the earth - Provide location within meters or less anywhere on the globe. - Created and operated by the US Department of Defense Finally – what is GPS?

- GPS uses a constellation of 27 Satellites 24 Active + 3 spare - Orbit the earth at Km - First satellite launched in 1978 – last one was launched in Signal used to be ‘scrambled’ – for Military reasons - In 2000 – this scrambling was removed - Handheld units are much more accurate and practical today. - A new set of European Satellites are about to go up – more accuracy!

- Satellites send signals to the GPS unit indicating their position in space and the exact time the signals are being sent - The GPS unit (or receiver) uses the time it takes signal to travel from the satellite to the receiver to determine distance from the satellite to the receiver - Information from multiple satellites is used to determine position through a method called ‘triangulation’

The basic concept behind GPS is simple: Let's say we're lost and we're trying to locate ourselves. If we know that we are a certain distance from satellite A, say 11,000 miles ( km), that really narrows down where in the whole universe we can be. It tells us we must be somewhere on an imaginary sphere (the earth) that is centered on the satellite and that has a radius of 11,000 miles. Triangulation

Now if at the same time we also know that we’re 12,000 miles (19 300km) from another satellite, satellite B, that narrows down where we can be even more. Because the only place in the universe where we can be 11,000 miles from satellite A and 12,000 miles from satellite B is on the circle where those two spheres intersect.

Then if we make a measurement from a third satellite we can really pinpoint ourselves. Because if we know that at the same time we're 13,000 miles (21 000km) from satellite C, there are only two points in space where that can be true. Those two points are where the 13,000 mile sphere cuts through the circle that intersects the 11,000 mile sphere and the 12,000 mile sphere.

How do we decide which of the two points is the correct one? We could make a fourth measurement, using a fourth satellite, or we can make an assumption. Usually one of the two points is a ridiculous answer, it may be off the earth at a very high altitude. GPS units, usually can eliminate the ridiculous point and figure the correct point from the incorrect one.

Most receivers can be as accurate as less than a metre.

GPS is not perfect?

What’s so cool about GPS? –Can be used as a digital compass –Can be used to determine ground speed –Can store landmarks (locations – called Waypoints) –Can store your route –New sport called ‘Geo-caching’ –Can track things –Can be used for mapping applications – Google Maps, Google Earth and GIS

The End!