GPS : Introduction

GPS :

      Every location on earth has a global address. Because the address is in numbers, people can communicate about location no matter what language they might speak. A global address is given as two numbers called coordinates. The two numbers are a location's latitude number and its longitude number ("Lat/Long").

The earth is divided in two lines latitude and longitude.lattitude lines runs east and west and measure north and south while longitude line runs north and south and measure east and west.longitude and latitude lines measure distance in degree. basically they all are imaginary lines. equator is 0 degree latitude .the prime maridian is 0 degree longitude.in other sense globe is network of longitudes and latitudes.

 

Each degree of latitude is approximately 69 miles (111 kilometers) apart. The range varies (due to the earth's slightly ellipsoid shape) from 68.703 miles (110.567 km) at the equator to 69.407 (111.699 km) at the poles. This is convenient because each minute (1/60th of a degree) is approximately one mile.

A degree of longitude is widest at the equator at 69.172 miles (111.321) and gradually shrinks to zero at the poles. At 40° north or south the distance between a degree of longitude is 53 miles (85 km).

Maths formula :

If you want Java Script to find out this: click  javascript

Distance

This uses the ‘haversine’ formula to calculate the great-circle distance between two points – that is, the shortest distance over the earth’s surface – giving an ‘as-the-crow-flies’ distance between the points (ignoring any hills they fly over, of course!).

Haversine formula:	a = sin²(Δφ/2) + cos φ1 ⋅ cos φ2 ⋅ sin²(Δλ/2) c = 2 ⋅ atan2( √a, √(1−a) ) d = R ⋅ c
where	φ is latitude, λ is longitude, R is earth’s radius (mean radius = 6,371km); note that angles need to be in radians to pass to trig functions!

There is a neat formula for this, which is easy to remember and easy to use if you have a scientific calculator. If S is the distance, L1 and L2 are the latitudes, and D is the difference in longitudes, then we have: 

cos S = (sin L1)(sin L2) + (cos L1)(cos L2)(cos D). 

This will give the distance in degrees or radians, from which a multiplication by a suitable constant will give you statute miles, nautical miles, kilometers, furlongs, or whatever.

         The global positioning system is a satellite based system which consists of 24 satellites. First satellite launched in 1978.Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the earth where there is an unobstructed line of sight to four or more GPS satellites. The system created and maintained by the United States government, which makes it freely accessible to anyone with a GPS receiver, provides critical capabilities to military, civil, and commercial users around the world.Roger L. Easton is credited with inventing the Global Positioning System (GPS) along with Bradford Parkinson and Ivan A. Getting. Easton developed a time-based navigational system with passive ranging, circular orbits, and space-borne high precision clocks placed in satellites, which was tested with four experimental satellites: TIMATION I and II (in 1967 and 1969) and Navigation Technology Satellites (NTS) 1 and 2 (in 1974 and 1977). NTS-2 was the first satellite to transmit GPS signals.

Some important dates of GPS

1990 first continuous GPS in California  

1994 international GPS service start

1994 beginning of SCIGN network

2000 GPS in every cell phone.

Satellite Transmission:

All radio signals in L-band, Frequency 1.5 GHz, and wavelength 20 cm

 Work Style of GPS:

for more information please go on pocket gps world.com

http://www.socialstudiesforkids.com/