GPS

Global Positioning System

What is GPS?

Global Positioning System (GPS) It is a satellite-based navigation system. Made up of a network of 24 satellites placed into orbit

by the u.s. department of defense. Gps was originally intended for military applications, but

in the 1980s, the government made the system available for civilian use.

Gps permits land, sea, and airborne users to determine their three-dimensional position, velocity, and time.

It can be used by anyone with a receiver anywhere on the planet, at any time of day or night, in any type of weather.

Segments• GPS uses radio transmissions. The satellites transmit

timing information and satellite location information. The system can be separated into three parts:

• Space segment

• Control Segment

User Segment

Figure illustrates how the three segments fit together

Space Segment

• The space segment consists of the satellites themselves. • According to the United state Naval observatory there

are currently 27 operational GPS satellites about 11,000 miles up in space.

• This constellation provides between five and eight GPS satellites visible from any point on the earth.

It takes each satellite about twelve hours to orbit the earth. There are six orbital planes with at least four satellites in each plane.

Control Segment

• The control segment is a group of ground stations that monitor and operate the GPS satellites. There are monitoring stations spaced around the globe and one Master Control Station located in Colorado Springs

There are actually five major monitoring systems, the figure below does not include the Hawaiian station

User Segment

• The user requires a GPS receiver in order to receive the transmissions from the satellites. The GPS receiver calculates the location based on signals from the satellites

• The users consist of both the military and civilians.

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How it works

• GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth.

• GPS receivers take this information and use triangulation to calculate the user's exact location.

• 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.

• 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 and track movement

• four or more satellites in view, the receiver can determine the user's 3D position

How accurate is GPS?

• GPS receivers are extremely accurate due to parallel multi-channel design.

• Garmin's 12 parallel channel receivers are quick to lock onto satellites when first turned on and they maintain strong locks, even in dense foliage or urban settings with tall buildings.

• Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers.

• GPS receivers are accurate to within 15 meters on average.

• GPS receivers with WAAS capability can improve accuracy to less than three meters on average.

• Users can also get better accuracy with Differential GPS (DGPS), which corrects GPS signals to within an average of three to five meters.

What's the signal?

• GPS satellites transmit two low power radio signals, designated L1 and L2.

• Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band.

• The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains.

A GPS signal contains three different bits of information

• pseudorandom code• ephemeris data • almanac data

Sources of GPS signal errors

Factors that can degrade the GPS signal and thus affect accuracy include the following:• Ionosphere and troposphere delays • Signal multipath • Receiver clock errors • Orbital errors • Number of satellites visible • Satellite geometry/shading • Intentional degradation of the satellite signal

Applications Of Global Positioning System

AUTOMOBILE

• Car Navigation• Dynamic Vehicle Routing • Tracking Rental Cars• Monitoring High Risk Auto Loans

AIRLINE SAFETY

• Aviation Safety• Aviation Security

AGRICULTURE AND FARMING

• Tractor Guidance• Crop-duster Targeting• Tracking Livestock• Yield Monitoring• Soil Sampling

LAW ENFORCEMENT

• Tracking Convicted/Suspected Criminals • Online Crime Maps • Appealing Speed Tickets

SPORTS

• Bicycle Racing• Athletic Training• GPS Golf • Soccer

Advantages of GPS:

• GPS is extremely easy to navigate as it tells you to the direction for each turns you take or you have to take to reach to your destination.

• GPS works in all weather so you need not to worry of the climate as in other navigating devices.

• The GPS costs you very low in comparison other navigation systems.

• The most attractive feature of this system is its100% coverage on the planet.

• It also helps you to search the nearby restaurants, hotels and gas stations and is very useful for a new place.

• Due to its low cost, it is very easy to integrate into other technologies like cell phone.

• The system is updated regularly by the US government and hence is very advance.

• This is the best navigating system in water as in larger water bodies we are often misled due to lack of proper directions.

Disadvantages of Global Positioning System

• Sometimes the GPS may fail due to certain reasons and in that case you need to carry a backup map and directions.

• These systems rely on batteries. Once the battery is drained out, the system does not work.

• Sometimes the GPS signals are not accurate due to some obstacles to the signals such as buildings, trees and sometimes by extreme atmospheric conditions such as geomagnetic storms.

• Price of the system is a major concern. GPS systems cost a high amount if they have lots of features.

• Accuracy is again an issue. The systems are not always updated, so we do not know when a road has been closed or when a new road has been opened.