Global positioning system report and ppt
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02-04-2010, 03:02 AM


Global Positioning System
Global Positioning System is an System to Identify the Position on Globe through a Network Of Satellites.
The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. It provides reliable positioning, navigation, and timing services to worldwide users. The Space, Control and User are the three segments of this . The User Segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service. The Space Segment is composed of 24 to 32 satellites in Medium Earth Orbit . The Control Segment is composed of a Master Control Station, an Alternate Master Control Station, and a host of dedicated and shared Ground Antennas and Monitor Stations.

Basic concept of GPS:
A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth. Each satellite continually transmits messages like, precise orbital information, the time the message was transmitted, system health and rough orbits.

Space segment:
It is is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. It has six planes with four satellites each and the six planes have approximately 55° inclination (tilt relative to Earth's equator) and are separated by 60° right ascension .

Control segment:
There are a)a Master Control Station (MCS),
b)Alternate Master Control Station
c)four dedicated Ground Antennas and
d)six dedicated Monitor Stations.

User segment:
It is is composed of U.S. and allied military users of the secure GPS Precise Positioning Service. civil, commercial and scientific users of the Standard Positioning Service come inder this segment. GPS receivers may include an input for differential corrections, using the RTCM SC-104 format. This is typically in the form of an RS-232 port at 4,800 bit/s speed. Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol

for more etails, visit the page:
en.wikipediawiki/Global_Positioning_System
Visit this link for a report:
geology.isu.edu/geostac/Field_Exercise/GPS/GPS_basics_u_blox_en.pdf

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02-04-2010, 03:54 PM

Find where your kids have been! Verify employee driving routes! Review family members driving habits! Watch large shipment routes! Know where anything or anyone has been! All this can be done merely by sitting at your own desk!

Finding your way across the land is an ancient art and science. The stars, the compass, and good memory for landmarks helped you get from here to there. Even advice from someone along the way came into play. But, landmarks change, stars shift position, and compasses are affected by magnets and weather. And if you've ever sought directions from a local, you know it can just add to the confusion. The situation has never been perfect. This has led to the search of new technologies all over the world .The outcome is THE GLOBAL POSITIONING SYSTEM. Focusing the application and usefulness of the GPS over the age-old challenge of finding the routes, this paper describes about the Global Positioning System, starting with the introduction, basic idea and applications of the GPS in real world.
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13-04-2010, 06:39 PM


.ppt   GPS & its applications.ppt (Size: 6.35 MB / Downloads: 1,252)

GLOBAL POSITIONING SYSTEM & ITS APPLICATIONS

PRESENTED BY :
KIRAN LAL A
ROLL NO 06238

CONTENTS
INTRODUCTION
HISTORY
ELEMENTS
PRINCIPLE OF OPERATION
MEASURING DISTANCE
SOURCES OF ERROR
APPLICATIONS

INTRODUCTION
GIS

It is a computerized information storage processing and retrieval system that has hardware and software especially designed to cope with geographical referenced spatial data

GIS

Techniques to input geographical information converting the information to digital form
Techniques for sorting information in a compact format on computer disk or digital storage media
Can analyze, make measurements and find optimum sites or routes and a hosts of other tasks
Can predict outcome of various scenarios, can display data in the form of maps, images etc
GPS HISTORY

LAUNCH OF SPUTNIK IN 1957
TRANSIT SYSTEM IN 1960
FIRST SATELLITE IN 1970
F.O.C (Full Operational Capacity) IN JULY 17 1995
$ 12 BILLION
NAVSTAR
DESIGNED BY U.S DoD
PRIMARY USE- MILITARY

GPS ELEMENTS

1. SPACE SEGMENT

2. CONTROL SEGMENT

3. USER SEGMENT

SPACE SEGMENT

24 SATELLITES IN A CONSTELLATION OF 6 ORBITAL PLANES, EACH SATELLITE COMPLETES 1 REVOLUTION IN 12 HOURS
6 ORBITS INCLINED 55 DEGREES FROM THE EQUATOR
4 SATELLITES FOR 3-D POSITIONING
This configuration provides for at least 4 equally spaced satellites within each of the orbital planes

SPACE SEGMENT
CONTROL SEGMENT
MONITOR STATIONS
MASTER CONTROL STATION
Frequency L1=1575.42 MHz C/A code, L2=1227.60 MHz P code

CONTROL SEGMENT
USER SEGMENT

CONSISTS OF GPS RECEIVER,ANTENNA AND PROCESSOR
SPS-STANDARD POSITIONING SERVICE
PPS-PRECISE POSITIONING SERVICE


PRINCIPLE OF OPERATION

TRILATERATION PRINCIPLE
A body cannot occupy 2 positions in space simultaneously

2D TRILATERATION
3D LATERATION

2-D TRILATERATION
3-D TRILATERATION
MEASURING DISTANCE





SATELLITE AND THE RECEIVER GENERATE SAME PSEUDO-RANDOM CODES AT THE SAME TIME

MEASURING HOW LONG THE SIGNAL TAKES TO REACH US

MULTIPLY THE TRAVEL TIME BY THE SPEED OF LIGHT

SOURCES OF ERROR


SOURCES OF ERROR

SIGNAL ARRIVAL TIME MEASUREMENT
CLOCK ERRORS
ATMOSPHERIC EFFECTS
MULTIPATH EFFECT
GEOMETRIC DILUTION OF PRECISION
SELECTIVE AVAILABILITY
APPLICATIONS


LOCATION

NAVIGATION

TRACKING

MAPPING

TIMING

LOCATION
NAVIGATION
TRACKING
MAPPING
TIMING
FIELDS OF APPLICATIONS


MILITARY

CIVILIAN

MILITARY
CIVILIAN
LAND NAVIGATION
AVIATION





ACCURATE POSITION DATA
SHORTEST ROUTES
SURVEYING





REDUCE AMOUNT OF LABOUR & EQUIPMENT

CONCLUSION

Satellite based navigational aid
Guided by 24 satellites round the globe in 6 orbits
3D positioning and time
Type of terrain and weather does not effect positioning
Cheap and precise operating equipment
Inherent error correction mode
A variant of GPS , DGPS has already been introduced

REFERENCES

GIS and Remote Sensing Applications in Environmental Management (Indian Institute of Science, Bangalore)
en.wikipedia.org
Trimbleâ„¢s online GPS tutorial
howstuffworks.com
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18-04-2010, 10:51 PM


.ppt   Seminar on GPS.ppt (Size: 603 KB / Downloads: 241)


GLOBAL POSITIONING SYSTEM

Why do we need GPS?
The Global Positioning System (GPS) is a space-based global navigation system.

It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth.

On the whole, GPS works efficiently with the help of satellite communication.



Components of the GPS


Space Segment:

The Space Segment is composed of 24 to 32 satellites in Medium earth orbit and also includes the boosters required to launch them into orbit.


Control Segment:

The control segment comprises of 5 stations.
They measure the distances of the overhead satellites every 1.5 seconds and send the corrected data to Master control.
Here the satellite orbit, clock performance and health of the satellite are determined and determines whether repositioning is required.
This information is sent to the three uplink stations


User Segment:

It consists of receivers that decode the signals from the satellites.

The receiver performs following tasks:
Selecting one or more satellites
Acquiring GPS signals
Measuring and tracking
Recovering navigation data
Emergence of GPS:
Before the invention of GPS, the device that is used for tracing is a micro tracing device, which is mainly used for tracing the movement of animals(mainly Birds).This device weighs nearly 1 to10 grams, which is fixed with the body of the animal.
How does the GPS work?

Requirements
Triangulation from satellite
Distance measurement through travel time of radio signals
Very accurate timing required
To measure distance the location of the satellite should also be known
Finally delays have to be corrected
Working process


GPS or Global Positioning System is a technology for locating a person or an object in three dimensional spaces anywhere on the Earth or in the surrounding orbit. GPS is a very important invention of our time on account of the many different possibilities it brings.

To understand the working of GPS we should mainly need to know the satellite communication, which includes three main links namely
~>Uplink
~>Downlink
~>Crosslink

Pictorial representation

Triangulation

Position is calculated from distance measurement
Mathematically we need four satellites but three are sufficient by rejecting the ridiculous answer
Measuring Distance
Distance to a satellite is determined by measuring how long a radio signal takes to reach us from the satellite
Assuming the satellite and receiver clocks are sync. The delay of the code in the receiver multiplied by the speed of light gives us the distance


Applications

Defense purpose
Recovery of theft
Tracing objects
In predicting purpose
In heart failure alert system
Unmanned control service (Artificial Intelligence).
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17-08-2010, 05:49 PM


.ppt   Seminar on GPS.ppt (Size: 896 KB / Downloads: 220)
Why do we need GPS?
Trying to figure out where you are is probable manâ„¢s oldest pastime.

Finally US Dept of Defense decided to form a worldwide positioning system.

Also known as NAVSTAR ( Navigation Satellite Timing and Ranging Global positioning system) provides instantaneous position, velocity and time information.

Components of the GPS
Space segment
control segment
user segment

Space Segment:
24 GPS space vehicles(SVs).
Satellites orbit the earth in 12 hrs.
6 orbital planes inclined at 55 degrees with the equator.
This constellation provides 5 to 8 SVs from any point on the earth.

Control Segment:

The control segment comprises of 5 stations.
They measure the distances of the overhead satellites every 1.5 seconds and send the corrected data to Master control.
Here the satellite orbit, clock performance and health of the satellite are determined and determines whether repositioning is required.
This information is sent to the three uplink stations

User Segment:
It consists of receivers that decode the signals from the satellites.

The receiver performs following tasks:
Selecting one or more satellites
Acquiring GPS signals
Measuring and tracking
Recovering navigation data

User Segment:
There are two services SPS and PPS
The Standard Positioning Service
SPS- is position accuracy based on GPS measurements on single L1 frequency C/A code
C/A ( coarse /acquisition or clear/access) GPs code sequence of 1023 pseudo random bi phase modulation on L1 freq

The Precise Position Service
PPS is the highest level of dynamic positioning based on the dual freq P-code
The P-code is a very long pseudo-random bi phase modulation on the GPS carrier which does not repeat for 267 days
Only authorized users, this consists of SPS signal plus the P code on L1 and L2 and carrier phase measurement on L2

Cross Correlation

Anti- spoofing denies the P code by mixing with a W-code to produce Y code which can be decoded only by user having a key.
What about SPS users?
They use cross correlation which uses the fact that the y code are the same on both frequencies
By correlating the 2 incoming y codes on L1 and L2 the difference in time can be ascertained
This delay is added to L1 and results in the pseudorange which contain the same info as the actual P code on L2

GPS Satellite Signal:
L1 freq. (1575.42 Mhz) carries the SPS code and the navigation message.
L2 freq. (1227.60 Mhz) used to measure ionosphere delays by PPS receivers
3 binary code shift L1 and/or L2 carrier phase
The C/A code
The P code
The Navigation message which is a 50 Hz signal consisting of GPs satellite orbits . Clock correction and other system parameters

How does the GPS work?
Requirements
Triangulation from satellite
Distance measurement through travel time of radio signals
Very accurate timing required
To measure distance the location of the satellite should also be known
Finally delays have to be corrected

Triangulation
Position is calculated from distance measurement
Mathematically we need four satellites but three are sufficient by rejecting the ridiculous answer

Measuring Distance

Distance to a satellite is determined by measuring how long a radio signal takes to reach us from the satellite
Assuming the satellite and receiver clocks are sync. The delay of the code in the receiver multiplied by the speed of light gives us the distance

Getting Perfect timing

If the clocks are perfect sync the satellite range will intersect at a single point.
But if imperfect the four satellite will not intersect at the same point.
The receiver looks for a common correction that will make all the satellite intersect at the same point

Error Sources
95% due to hardware ,environment and atmosphere
Intentional signal degradation
Selective availability
Anti spoofing

Selective Availabity

Two components
Dither :
manipulation of the satellite clock freq

Epsilon:
errors imposed within the ephemeris data sent in the broadcast message

Anti spoofing
Here the P code is made un gettable by converting it into the Y code.
This problem is over come by cross correlation

DGPS
Errors in one position are similar to a local area
High performance GPS receiver at a known location.
Computes errors in the satellite info
Transmit this info in RTCM-SC 104 format to the remote GPS

Requirements for a DGPS
Reference station:
Transmitter
Operates in the 300khz range
DGPS correction receiver
Serial RTCM-SC 104 format
GPS receiver

Data Links
Land Links
MF,LF,UHF/VHF freq used
Radiolocations,local FM, cellular telephones and marine radio beacons
Satellite links
DGPS corrections on the L band of geostaionary satellites
Corrections are determined from a network of reference Base stations which are monitored by control centers like OmniSTAR and skyFix

RTCM-SC 104 format
DGPS operators must follow the RTCM-SC 104 format
64 messages in which 21 are defined
Type 1 contains pseudo ranges and range corrections,issue of data ephemeris (IODE)and user differential range error(URDE)
The IODE allows the mobile station to identify the satellite navigation used by the reference station.
UDRE is the differential error determined by the mobile station

DGPS
DGPS gives accuracy of 3-5 meters,while GPS gives accuracy of around 15-20 mts

Removes the problem associated with SA.


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16-10-2010, 11:58 AM



.ppt   GPS Presentation.ppt (Size: 1.32 MB / Downloads: 153)


Introduction

Global Positioning System (GPS) is a world-wide navigational system that can tell you with pinpoint accuracy your exact current location.

Global Positioning System, commonly known as GPS system, was the 1st satellite navigation system. It was launched in 1978 and is technically known as NAVSTAR GPS (Navigation Satellite with Timing and Ranging Global Positioning System ).

The GPS system was initially developed as a navigation aid for the military, however later it was made available to civilians as well & is now used in everyday life. But to keep the military applications at priority the United States Department of Defence provides two levels of GPS positioning & timing service.
(i) The Precise Positioning Service (PPS)
(ii) The standard Positioning Service (SPS)
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19-10-2010, 12:42 PM


Global positioning system report and ppt

INTRODUCTION

Have u ever been lost and wished there was an easy way to find out which way u
needed to go? How about finding yourself out hiking and then not knowing how
to get back to your camp or car? Ever been flying and wanted to know the
nearest airport?
Our ancestors had to go to pretty extreme measures to keep from getting lost.
They erected monumental landmarks, laboriously drafted detailed maps and
learned to read the stars in the night sky.
GPS is a satellite based radio navigation system which provides continuous, all
weather, worldwide navigation capability for sea, land and air applications. So
things are much, much easier today. For less than $100, you can get a pocketsized
gadget that will tell you exactly where you are on Earth at any moment. As
long as you have a GPS receiver and a clear view of the sky, you'll never be lost
again.
Navigation in three dimensions is the primary function of GPS. Navigation
receivers are made for aircraft, ships, ground vehicles, and for hand carrying by
individuals. Precise positioning is possible using GPS receivers at reference
locations providing corrections and relative positioning data for remote
receivers. Surveying, geodetic control, and plate tectonic studies are examples.
Time and frequency dissemination, based on the precise clocks on board the SVs
and controlled by the monitor stations, is another use for GPS. Astronomical
observatories, telecommunications facilities, and laboratory standards can be set
to precise time signals or controlled to accurate frequencies by special purpose
GPS receivers.

for more :-
forests.tn.nicgeomatics/globalpositioningsystem.html

gisdevelopmenttechnology/gps/techgp0038.htm
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24-12-2010, 04:35 PM



.ppt   gps final presentation.ppt (Size: 1.81 MB / Downloads: 129)

By – Rajkaran Chauhan


WHAT IS GPS
GPS, which stands for Global Positioning System, As the name suggest it is a system to find out your location any where and anytime on the surface or near the earth surface. Developed by the United States Department of Defense, GPS is officially named NAVSTAR-GPS.

At 12,600 miles (20,200 km) altitude. (12 hour orbit period).
30 satellites (24+6) with 6 spare space Vehicles or SVs.
6 orbital planes (55° inclination).
4 satellites in each plane. Monitored by 5 ground control stations.
Manufactured by Rockwell International, later by Lockheed M&S
Satellite weighs ~1900 lbs, 2.2m body, 7m with solar panels.
7-10 year expected lifetime.
GPS satellites use Atomic Clocks for accuracy, but because of the expense, most GPS receivers do not.
It works by using radio frequency broadcast from the orbiting satellite.
Civilian units only receive the L1 frequency.
History and facts
Started development in 1973.First four satellites launched in 1978.
Full Operational Capacity (FOC) reached on July 17, 1995.
In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.
3 satellite signals are necessary to locate the receiver in 3D space 4th satellite is used for time accuracy.
GPS receiver uses latitude, longitude, and altitude to calculate its three-dimensional location
The most recent launch was on May 28, 2010.The oldest GPS satellite still in operation was launched on November 26, 1990.
Glonas and Galileo are another positioning system developed by Russia and European union respectively Glonas-24 and Galileo -30












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.docx   ajay-Global positioning system.docx (Size: 932.53 KB / Downloads: 108)


Introduction

The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth.
GPS is made up of three parts: between 24 and 32 satellites orbiting the Earth, four control and monitoring stations on Earth, and the GPS receivers owned by users. GPS satellites broadcast signals from space that are used by GPS receivers to provide three-dimensional location (latitude, longitude, and altitude) plus the time.
Since it became fully operational on April 27, 1995, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, scientific uses, tracking and surveillance, and hobbies such as geocaching and waymarking. Also, the precise time reference is used in many applications including the scientific study of earthquakes and as a time synchronization source for cellular network protocols.
GPS has become a mainstay of transportation systems worldwide, providing navigation for aviation, ground, and maritime operations. Disaster relief and emergency services depend upon GPS for location and timing capabilities in their life-saving missions. Everyday activities such as banking, mobile phone operations, and even the control of power grids, are facilitated by the accurate timing provided by GPS. Farmers, surveyors, geologists and countless others perform their work more efficiently, safely, economically, and accurately using the free and open GPS signals.

History


The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology that GPS relies upon. In the 1970s, the ground-based Omega Navigation System, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Friedwardt Winter berg proposed a test of General Relativity using accurate atomic clocks placed in orbit in artificial satellites. To achieve accuracy requirements, GPS uses principles of general relativity to correct the satellites' atomic clocks.
The design of GPS is based partly on similar ground-based radio navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II. Additional inspiration for the GPS came when the Soviet Union launched the first man-made satellite, Sputnik in 1957. A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions. They discovered that, because of the Doppler Effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.
After Korean Air Lines Flight 007 was shot down in 1983 after straying into the USSR's prohibited airspace, President Ronald Reagan issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good. The first satellite was launched in 1989 and the 24th and last satellite was launched in 1994.
Initially the highest quality signal was reserved for military use, and the signal available for civilian use intentionally degraded ("Selective Availability", SA). Selective Availability was ended in 2000, improving the precision of civilian GPS from about 100m to about 20m.

Working of GPS

A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth. Each satellite continually transmits messages which include

the time the message was sent
precise orbital information (the ephemeris)
the general system health and rough orbits of all GPS satellites.
The receiver measures the transit time of each message and computes the distance to each satellite. Geometric trilateration is used to combine these distances with the satellite’s locations to obtain the position of the receiver. This position is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included. Many GPS units also show derived information such as direction and speed, calculated from position changes.
Three satellites might seem enough to solve for position, since space has three dimensions. However, even a very small clock error multiplied by the very large speed of light, the speed at which satellite signals propagate, results in a large positional error. Therefore receivers use four or more satellites to solve for the receiver's location and time. The very accurately computed time is effectively hidden by most GPS applications, which use only the location. A few specialized GPS applications do however use the time; these include time transfer, traffic, signal timing, and synchronization of cell phone base stations.
Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. (For example, a ship or plane may have known elevation.) Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a degraded position when fewer than four satellites are visible.
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.pptx   Global Positioning System (GPS).pptx (Size: 614.96 KB / Downloads: 103)
Global Positioning System (GPS)
What is GPS ?

 world wide radio-navigation system formed from a constellation of 24 satellites.
 provides continuous three-dimensional positioning 24 hours a day.
 GPS provides specially coded satellite signals that can be processed with a GPS receiver.
Three Parts
 Space segment
 Control Segment
 User segment
How Does a GPS Work?
 GPS satellites circle the earth twice a day in the same orbit .
 use triangulation to calculate the user's exact location.
 compares the time a signal was transmitted by a satellite with the time it was received.
How GPS Determines a Location:
 calculating the distances between the receiver and the position of 3 or more satellites.
 Adding additional spheres will further reduce the number of possible locations
Computing the Distance
 measuring the amount of time it takes a radio signal to travel from the satellite to the receiver.
 distance = speed x time
Uses of GPS Technology
 The main purpose of these devices was for mapping locations.
 adjust to different time zones when users travel.
 keep an eye on their children.
 during war to keep track of every soldier's location and movements.
Factors that can degrade the GPS signal
 Signal multipath
 Receiver clock errors
 Number of satellites visible

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.docx   What is GPS.docx (Size: 115.37 KB / Downloads: 109)
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 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 works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.
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. 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 unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.
How accurate is GPS?
Today's GPS receivers are extremely accurate, thanks to their 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. Garmin® GPS receivers are accurate to within 15 meters on average.
Newer Garmin GPS receivers with WAAS (Wide Area Augmentation System) capability can improve accuracy to less than three meters on average. No additional equipment or fees are required to take advantage of WAAS. Users can also get better accuracy with Differential GPS (DGPS), which corrects GPS signals to within an average of three to five meters. The U.S. Coast Guard operates the most common DGPS correction service. This system consists of a network of towers that receive GPS signals and transmit a corrected signal by beacon transmitters. In order to get the corrected signal, users must have a differential beacon receiver and beacon antenna in addition to their GPS.
The GPS satellite system
The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are travelling at speeds of roughly 7,000 miles an hour.
GPS satellites are powered by solar energy. They have backup batteries onboard to keep them running in the event of a solar eclipse, when there's no solar power. Small rocket boosters on each satellite keep them flying in the correct path.
Here are some other interesting facts about the GPS satellites (also called NAVSTAR, the official U.S. Department of Defense name for GPS):
o The first GPS satellite was launched in 1978.
o A full constellation of 24 satellites was achieved in 1994.
o Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
o A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
o Transmitter power is only 50 watts or less.
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 - a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information. You can view this number on your Garmin GPS unit's satellite page, as it identifies which satellites it's receiving.
Ephemeris data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position.
The almanac data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits almanac data showing the orbital information for that satellite and for every other satellite in the system.
Sources of GPS signal errors
Factors that can degrade the GPS signal and thus affect accuracy include the following:
o Ionosphere and troposphere delays - The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error.
o Signal multipath - This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.
o Receiver clock errors - A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors.
o Orbital errors - Also known as ephemeris errors, these are inaccuracies of the satellite's reported location.
o Number of satellites visible - The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.
o Satellite geometry/shading - This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.
o Intentional degradation of the satellite signal - Selective Availability (SA) is an intentional degradation of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.
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.ppt   GPS.ppt (Size: 1.31 MB / Downloads: 128)
GLOBAL POSITIONING SYSTEM
INTRODUCTION

 GPS is a Global Navigation Satellite System(GNSS).
 Uses a constellation of at least 24 satellites orbiting around the earth.
 Transmits precise microwave signals, enabling GPS receivers to determine their location, speed, direction and time.
 First developed by United States Department of Defense- official name is NAVSTAR-GPS.
 GPS satellite navigation system includes
* Russian GLONASS
* European Galileo positioning system.
* Compass navigation system of China.
* IRNSS of India.
 Fig: GPS Navigation
2. TECHNICAL DESCRIPTION
2.1 System Segmentation

GPS consists of three major segments:
 Space Segment(SS)
 Control Segment(CS)
 User Segment(US)
Fig: Segments of Navigation
2.1.1 Space Segment:
• Comprises the orbiting GPS satellites or Space Vehicles(SV) in GPS parlance.
• GPS design originally called for 24 SVs, 8 in each three circular orbital planes. Now modified to 6 planes with 4 satellites each.
• Orbiting at an altitude of approx. 20,200 km, each SV makes two complete orbits.
2.1.2 Control Segment:
 The flight paths of the satellites tracked by US Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado.
 The tracked information sent to the Air Force Space Commands master control station at Schriever Operation Squadron(2 SOPS) of USAF.
 SOPS contacts each GPS satellites regularly with a navigational updates which are created by a Kalman filter using inputs from the ground monitoring stations, space weather information.
2.1.3 User Segment:
 GPS receiver is the user segment of GPS.
 GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock.
 It include a display for providing location and speed information to the user.
 A receiver is often described by its number of channels: signifies how many satellites it can monitor simultaneously.
2.2 Navigation Signals:
 Each GPS satellites broadcasts a Navigation Message at 50 bits/sec giving the time-of-week, GPS week number and satellite
* health information (all transmitted in the first part of the message).
* ephemeris( transmitted in the second part of the message).
* almanac(later part of the message).
• The messages are sent in frames, each taking 30 sec to transmit 1500 bits. The first 6 sec of every frame contains data describing the satellite clock & its relationship to GPS time.
• The next 12 sec contain the ephemeris data, giving the satellite’s own precise orbit.
• The almanac consists of coarse orbit and status information for each satellite in the constellation, an ionospheric model & information to relate GPS derived time to Coordinated Universal Time(UTC).
2.2 Navigation Signals
 Each satellite transmits its navigation message with at least two distinct spread spectrums codes:
* Coarse/Acquisition (C/A) code.
* Precise(P) code.
(C/A) code:
 It is freely available to the public.
 C/A code is 1023 chip pseudo-random number(PRN) code at 1.023 million chips per second so that it repeats every millisecond.
 Each satellite has its own C/A code so that it can be uniquely identified and received separately from other satellites transmitting on the same frequency.
2.2 Navigation Signals:
 Precise(P) code:
 It is encrypted and reserved for military applications.
 It is a 1023 mega chip per second PRN code that repeats only every week.
 P code is encrypted by the Y-code to produce the P(Y) code, which can only by decrypted by units with a valid decryption key.
 Both C/A and P(Y) codes impart the precise time-of-day to the user.
2.3 GPS Frequencies:
2.4 Accuracy and error sources:
2.4.1 Atmospheric Effects:

* The travel time of GPS satellite signals can be altered by atmospheric effects; when a GPS signal passes through the ionosphere and troposphere it is refracted, causing the speed of the signal to be different from the speed of a GPS signal in space. Sunspot activity also causes interference with GPS signals.
2.4.2 Multipath Effects:
* It arises when signals transmitted from the satellites bounce
off a reflective surface before getting to the receiver antenna.
When this happens, the receiver gets the signal in straight
line path as well as delayed path (multiple paths). The effect
is similar to a ghost or double image on a TV set.
2.4.3 Ephemeris and Clock errors:
* Errors in the ephemeris data (the information about satellite orbits) will also cause errors in computed positions, because the satellites weren't really where the GPS receiver "thought" they were (based on the information it received) when it computed the positions.
* Small variations in the atomic clocks (clock drift) on board the satellites can translate to large position errors; a clock error of 1 nanosecond translates to 1 foot or 0.3 meters user error on the ground.
2.4.4 Selective Availability:
 Selective Availability, or SA, occurred when the DoP(Dilution of Precision)
intentionally degraded the accuracy of GPS signals by introducing artificial clock and ephemeris errors.
 When SA was implemented, it was the largest component of GPS error, causing error of up to 100 meters. SA is a component of the Standard Positioning Service (SPS),
which was formally implemented on March 25, 1990, and was intended to protect national defense. SA was turned off on May 1, 2000.
2.4 Accuracy & error sources:
2.4.5 Sagnac Distortion

 GPS observation processing must also compensate for the Sagnac effect. Ignoring this effect will produce an east-west error on the order of hundreds of nanoseconds, or tens of meters in position.
*Potential errors are one of several accuracy-degrading effects outlined in the table below:
2.5 GPS Interference & Jamming:
2.5.1 Natural sources:

 Since GPS signals at terrestrial receivers tend to be relatively weak, it is easy for other sources of electromagnetic radiation to desensitize the receiver, making acquiring and tracking the satellite signals difficult or impossible.
 Solar flares are one such naturally occurring emission with the potential to degrade GPS reception, and their impact can affect reception over the half of the Earth facing the sun.
 GPS signals can also be interfered with by naturally occurring geomagnetic storms, predominantly found near the poles of the Earth's magnetic field.
2.5.2 Artificial sources:
 In automotive GPS receivers, metallic features in windshields such as defrosters, or car window tinting films can act as a Faraday cage, degrading reception just inside the car.
 Man-made EMI (electro-magnetic interference) can also disrupt, or jam, GPS signals.
 Stronger signals can interfere with GPS receivers when they are within radio range, or line of sight.
3.Techniques to improve accuracy:
3.1 Augmentation:

 This method of improving accuracy rely on external information being integrated into calculation process.
 Examples of augmentation systems include the Wide Area Augmentation System, Differential GPS, Inertial Navigation Systems and Assisted GPS.
3.2 Precise Monitoring:
• This method uses two approaches:
 Carrier-Phase Enhancement(CPGPS)
 Relative Kinematic Positioning(RKP)
3.Techniques to improve accuracy:
CPGPS:
* This technique resolve the uncertainty that arises in GPS due to pulse transition of PRN is not instantaneous & thus correlation operation is imperfect.
* It utilizes the L1 carrier wave to resolve the uncertainty.
RKP:
*In this approach, determination of range signal can be resolved to a precision of less than 10cm. This is done by resolving the number of cycles in which the signal is transmitted and received the receiver.
3.Techniques to improve accuracy:
3.3 GPS time and date:

* While most clocks are synchronized to Coordinated Universal Time (UTC), the atomic clocks on the satellites are set to GPS time. The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections which are periodically added to UTC.
* To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal.
3.4 GPS modernization:
*This approach aims to improve the accuracy and availability for all users and involves new ground stations, new satellites & four additional navigation signals.
4.Applications:
GPS has significant applications for both military and civilian industry.
Military Applications:
 Navigation
 Target tracking
 Missile and project and implimentationile guidance
 Search and rescue
 Map creation
4.Applications:
Civilian:
 GPS receivers act as a surveying tool to determine the absolute location.
 GPS enables researchers to explore the Earth environment including the atmosphere, ionosphere & gravity field.
 The capacity to determine relative movement enables a receiver to calculate local velocity & orientation, useful in vessels or observations of the Earth.
5.Conclusion
 GPS continues to perform as the world’s premier space-based positioning, navigation and timing-service.
 Endeavors such as mapping, aerial refueling, geodetic surveying, search & rescue operations have all benefitted greatly from GPS’s accuracy.
 GPS receivers are incorporated into every type of system used by aircraft, ground vehicles and ships.
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30-03-2011, 10:51 AM

Presented by:
Nipun Tripathi


.ppt   PreWork.ppt (Size: 974 KB / Downloads: 65)
Global Positioning System
User Segment

 Military.
 Search and rescue.
 Disaster relief.
 Surveying.
 Marine, aeronautical and terrestrial navigation.
 Remote controlled vehicle and robot guidance.
 Satellite positioning and tracking.
 Shipping.
 Geographic Information Systems (GIS).
 Recreation
Four Primary Functions of GPS
 Position and coordinates.
 The distance and direction between any two waypoints, or a position and a waypoint.
 Travel progress reports.
 Accurate time measurement.
Position Fix
 A position is based on real-time satellite tracking.
 It’s defined by a set of coordinates.
 It has no name.
 A position represents only an approximation of the receiver’s true location.
 A position is not static. It changes constantly as the GPS receiver moves (or wanders due to random errors).
 A receiver must be in 2D or 3D mode (at least 3 or 4 satellites acquired) in order to provide a position fix.
 3D mode dramatically improves position accuracy.
Waypoint
 A waypoint is based on coordinates entered into a GPS receiver’s memory.
 It can be either a saved position fix, or user entered coordinates.
 It can be created for any remote point on earth.
 It must have a receiver designated code or number, or a user supplied name.
 Once entered and saved, a waypoint remains unchanged in the receiver’s memory until edited or deleted.
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07-04-2011, 03:07 PM


.ppt   gps-1216310990826489-9.ppt (Size: 282.5 KB / Downloads: 54)
GLOBAL POSITIONING SYSTEM
1. INTRODUCTION

 Trying to figure out where you are and where you're going is probably one of man's oldest pastimes. Navigation and positioning are crucial to so many activities and yet the process has always been quite complicated .
 So the result is the Global Positioning System, a system that's changed navigation forever.
2. WHAT IS GPS ?
 The Global Positioning System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their groundstations.There are 5 ground stations: Hawaii, Ascension Island, Diego Garcia, Kwajalein, and Colorado Springs.
3. FACTS ABOUT GPS !
 The first GPS satellite was launched in 1978.
 A full constellation of 24 satellites was achieved in 1994.
 Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
 A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
 Transmitter power is only 50 watts or less.
4. HOW GPS WORKS?
Here's how GPS works in five logical steps:
 The basis of GPS is “triangulation” from satellites.
 To "triangulate," a GPS receiver measures distance using the travel time of radio signals.
 To measure travel time, GPS needs very accurate timing which it achieves with some tricks.
 Along with distance, you need to know exactly where the satellites are in space. High orbits and careful monitoring are the secret.
 Finally you must correct for any delays the signal experiences as it travels through the atmosphere .
5.What's the signal?
 GPS receivers 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.
 In the case of GPS we're measuring a radio signal so the velocity is going to be the speed of light or roughly 186,000 miles per second.
 The timing problem is tricky. First, the times are going to be awfully short. If a satellite were right overhead the travel time would be something like 0.06 seconds. So we're going to need some really precise clocks, called atomic clocks, equipped in the satellites.
 Now the Distance = Velocity X Time
 So Distance= 1,86,000 X 0.06
 =11,160 miles.
 A GPS signal contains three different bits of information —
1.A pseudorandom code
2.Ephemeris data
3.Almanac data.
ERRORS
 Sometimes errors are occurred while the data are transmitted from the satellites to the GPS receivers.
 Ionosphere and troposphere delays —
 Signal multipath —
 Receiver clock errors —
 Orbital errors —
 Number of satellites visible —
 Satellite geometry/shading —
 Intentional degradation of the satellite signal —
CORRECTING ERRORS
 1. Some errors can be factored out using mathematics and modeling.
 2. The configuration of the satellites in the sky can magnify other errors.
 3. Differential GPS can eliminate almost all error.
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PRESENTED BY:
Mr.Prashant Kumar & Mr. Sugat Misra


.doc   GLOBAL POSITIONING SYSTEM.DOC (Size: 82 KB / Downloads: 61)
GLOBAL POSITIONING SYSTEM
ABSTRACT
Global Positioning System (GPS) is the only system today able to show ones own position on the earth any time in any weather, anywhere. This paper addresses this satellite based navigation system at length. The different segments of GPS viz. space segment, control segment, user segment are discussed. In addition, how this amazing system GPS works, is clearly described. The various errors that degrade the performance of GPS are also included. DIFFERENTIAL GPS, which is used to improve the accuracy of measurements, is also studied. The need, working and implementation of DGPS are discussed at length. Finally, the paper ends with advanced application of GPS.
INTRODUCTION:
The Global Positioning System (GPS) is a satellite-based navigation system developed and operated by the US Department of Defense. GPS permits land, sea and airborne users to determine their three-dimensional position, velocity and time. This service is available to military and civilian users around the clock, in all weather, anywhere in the world.
The main principle behind the GPS system is “a transmitter high above the Earth sending a high-frequency radio wave with a special coded signal can cover a large area and still overcome much of the "noise" encountered on the way to the ground”.
GPS ELEMENTS:
GPS has 3 parts: the space segment, the user segment, and the control segment. The space segment consists of 24 satellites, each in its own orbit 11,000 nautical miles above the Earth. The user segment consists of receivers, which you can hold in your hand or mount in your car. The control segment consists of ground stations (five of them, located around the world) that make sure the satellites are working properly.
ELEMENTS OF GLOBAL POSITIONING SYSTEM
SPACE SEGMENT:

The complete GPS space system includes 24 satellites, 11,000 nautical miles above the Earth, which take 12 hours each to go around the Earth once (one orbit). They are positioned so that we can receive signals from six of them nearly 100 percent of the time at any point on Earth. There are six orbital planes (with nominally four Space Vehicles in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane.Satellites are equipped with very precise clocks that keep accurate time to within three nanoseconds. This precision timing is important because the receiver must determine exactly how long it takes for signals to travel from each GPS satellite. The receiver uses this information to calculate its position.
The first GPS satellite was launched in 1978. The first 10 satellites were developmental satellites, called Block I. From 1989 to 1993, 23 production satellites, called Block II, were launched. The launch of the 24 satellites in 1994 completed the system. The control segment consists of a worldwide system of tracking and monitoring stations.The 'Master Control Facility' is located at Falcon AFB in Colorado Springs, CO.
The monitor stations measure signals from the GPS satellites and relay the information they collect to the Master Control Station. The Master Control Station uses this data to compute precise orbital models for the entire GPS constellation. This information is then formatted into updated navigation messages for each satellite.
USER SEGMENT:
The user segment consists of the GPS receivers, processors and antennas utilized for positioning and timing by the community and military. The GPS concept of operation is based on satellite ranging. Users figure their position on the earth by measuring their
distance to a group of satellites in space. Each GPS satellite transmits an accurate
position and time signal. The user's receiver measures the time delay for the signal to
reach the receiver. By knowing the distance to four points in space, the GPS receiver is
able to triangulate a three-dimensional position.
WORKING OF GPS:
The principle behind GPS is the measurement of distance (or "range") between the receiver and the satellites. The satellites also tell us exactly where they are in their orbits above the Earth. Four satellites are required to compute the four dimensions of X, Y, Z (position) and Time. GPS receivers are used for navigation, positioning, time dissemination, and other research.
One trip around the Earth in space equals one orbit. The GPS satellites each take 12 hours to orbit the Earth. Each satellite is equipped with an accurate clock to let it broadcast signals coupled with a precise time message. The ground unit receives the satellite signal, which travels at the speed of light. Even at this speed, the signal takes a measurable amount of time to reach the receiver. The difference between the time the signal is sent and the time it is received, multiplied by the speed of light, enables the receiver to calculate the distance to the satellite. To measure precise latitude, longitude, and altitude, the receiver measures the time it took for the signals from four separate satellites to get to the receiver.
It works something like this: If we know our exact distance from a satellite in space, we know we are somewhere on the surface of an imaginary sphere with radius equal to the distance to the satellite radius. If we know our exact distance from two satellites, we know that we are located somewhere on the line where the two spheres intersect. And, if we take a third measurement, there are only two possible points where we could be located. By taking the measurement from the fourth satellite we can exactly point out our location.
SOURCES OF GPS SIGNAL ERRORS:
Factors that can degrade the GPS signal and thus affect accuracy include the following-
• Ionosphere and troposphere delays — The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error.
• Signal multi path — This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.
• Orbital errors — Also known as ephemeris errors, these are inaccuracies of the satellite's reported location.
• Number of satellites visible — The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.
• Satellite geometry/shading — This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.
DIFFERENTIAL GPS:
NEED FOR DGPS:

As the GPS receivers use timing signals from at least four satellites to establish a position, each of those timing signals is going to have some error or delay, depending on what sort of perils have befallen it on its trip down to receiver. Since each of the timing signals that go into a position calculation has some error, that calculation is going to be a compounding of those errors.
The sheer scale of the GPS system solves the problem. The satellites are so far out in space that the little distances we travel here on earth are insignificant. So if two receivers are fairly close to each other, say within a few hundred kilometers, the signals that reach both of them will have traveled through virtually the same slice of atmosphere, and so will have virtually the same errors.
WORKING:
The underlying premise of differential GPS (DGPS) is that any two receivers that are relatively close together will experience similar atmospheric errors.
Differential GPS involves the cooperation of two receivers, one that's stationary and another that's roving around making position measurements. Since the reference receiver has no way of knowing which of the many available satellites a roving receiver might be using to calculate its position, the reference receiver quickly runs through all the visible satellites and computes each of their errors. Then it encodes this information into a standard format and transmits to the roving receivers. It's as if the reference receiver is saying: "OK everybody, right now the signal from satellite #1 is ten nanoseconds delayed, satellite #2 is three nanoseconds delayed, satellite #3 is sixteen nanoseconds delayed..." and so on.The roving receivers get the complete list of errors and apply the corrections for the particular satellites they're using.
IMPLEMENTING DGPS:
The three main methods currently used for ensuring data accuracy are real-time differential correction, reprocessing real-time data, and post processing.
1.REAL TIME DGPS
Real-time DGPS occurs when the base station calculates and broadcasts corrections for each satellite as it receives the data. The roving receiver via a radio signal receives the correction, if the source is land based or via a satellite signal, if it is satellite based and applied to the position it is calculating. As a result, the position displayed and logged to the data file of the roving GPS receiver is a differential corrected procedure.
2. REPROCESSING REAL TIME DATA:
Some GPS manufacturers provide software that can correct GPS data that was collected in real time. This is important for GIS data integrity. When collecting real-time data, the line of sight to the satellites can be blocked or a satellite can be so low on the horizon that it provides only a weak signal, which causes spikes in the data. Reprocessing real-time data removes these spikes and allows real-time data that has been used in the field for navigation or viewing purposes to be made more reliable before it is added to a GIS.
3. POST PROCESSING CORRECTION:
Differentially correcting GPS data by post processing uses a base GPS receiver that logs positions at a known location and a rover GPS receiver that collects positions in the field. The files from the base and rover are transferred to the office processing software, which computes corrected positions for the rover's file. This resulting corrected file can be viewed in or exported to a GIS.
Thus, Differential GPS or "DGPS" can yield measurements good to a couple of meters in moving applications and even better in stationary situations. That improved accuracy has a profound effect on the importance of GPS as a resource. With it, GPS becomes more than just a system for navigating boats and planes around the world. It becomes a universal measurement system capable of positioning things on a very precise scale.
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