Login

m_k_sudhir · 10-04-2017, 09:37 PM

[attachment=14802]
Global Positioning System (GPS)
Introduction
The current global positioning system (GPS) is the culmination of years of research and unknown millions of dollars.
Navigational systems have been and continue to be developed and funded by the U.S. government.
The current system is managed by the U.S Air Force for the Department of Defense (DOD).
The current system became fully operational June 26, 1993 when the 24th satellite was lunched.
While there are millions of civil users of GPS worldwide, the system was designed for and is operated by the U. S. military.
Introduction-History
Introduction-History
Introduction--cont.
GPS provides specially coded satellite signals that can be processed with a GPS receiver, enabling the receiver to compute position, velocity and time.
A minimum of four GPS satellite signals are required to compute positions in three dimensions and the time offset in the receiver clock.
Accuracy and precision of data increases with more satellites.
Three Parts
Space segment
Control segment
User segment
Space Segment
The Air force insures that at least 24 satellites are operational at all times.
There are six orbital planes (with nominally four space vehicles (SVs) in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane.
The satellite orbits are controlled so that at least six should be available, unobstructed location, at all times.
Each satellite circles the earth twice a day.
Control Segment
The Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in Colorado.
Control Segment--cont.
User Segment
The primary use of GPS is navigation.
Navigation receivers are made for aircraft, ships, ground vehicles, surveying, and for hand carrying by individuals.
The accuracy of a receiver depends on the number of channels, compatibility with other navigational systems (WAAS, GLONAS, etc.) and design of the receiver (cost).
User Segment--cont.
The GPS User Segment consists of all GPS receivers.
Surveying
Recreation
Navigation
GPS receivers convert satellite signals into position, velocity, and time estimates.
Four satellites are required to compute the four dimensions of X, Y, Z (position) and Time.
User Segment--cont.
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.
The GPS signals are available to everyone, and there is no limit to the number and types of applications that use them.
Principles
The GPS system operates on the principles of trilateration, determining positions from distance measurements.
This can be explained using the velocity equation.
Trilateration Example
The signals from the GPS satellites travel at the speed of light--186,000 feet/second.
How far apart are the sender and the receiver if the signal travel time was 0.23 seconds?
Satellite Signals
Each satellite has its own unique signal.
It continuously broadcasts its signal and also sends out a time stamp every time it starts.
The receiver has a copy of each satellite signal and determines the distance by recording the time between when the satellite says it starts its signal and when the signal reaches the receiver.
GPS Trilateration
Each satellite knows its position and its distance from the center of the earth.
Each satellite constantly broadcasts this information.
With this information the receiver tries to calculate its position.
Just knowing the distance to one satellite doesn t provide enough information.
GPS Trilateration--cont.
When the receiver knows its distance from only one satellite, its location could be anywhere on the earths surface that is an equal distance from the satellite.
All the receiver can determine is that it is some where on the perimeter of a circle that is an equal distance from the satellite.
The receiver must have additional information.
GPS Trilateration--cont.
With signals from two satellites, the receiver can narrow down its location to just two points on the earths surface.
GPS Trilateration--cont.
Knowing its distance from three satellites, the receiver can determine its location because there is only two possible combinations and one of them is out in space.
In this example, the receiver is located at b.
Most receivers actually require four to insure the receiver has full information on time, and satellite positions.
The more satellite positions that are used, the greater the potential accuracy of the position location.
Factors Influencing Position Accuracy
The number of satellites (channels) the receiver can track.
The number of channels a receiver has is part of it s design.
The higher the number of channels--the greater the potential accuracy.
The higher the number of channels--the greater the cost.
The number of satellites that are available at the time.
Because of the way the satellites orbit, the same number are not available at all times.
When planning precise GPS measurements it is important to check for satellite availability for the location and time of measurement.
If a larger number of channels are required (6-10), and at the time of measurement the number available was less than that, the data will be less accurate.
Factors Influencing Position Accuracy--cont.
The system errors that are occurring during the time the receiver is operating.
The GPS system has several errors that have the potential to reduce the accuracy.
To achieve high levels of precision, differential GPS must be used.
Differential GPS uses one unit at a known location and a rover.
The stationary unit compares its calculated GPS location with the actual location and computes the error.
The rover data is adjusted for the error.
Real Time Kinematic (RTK)
Post processing
Location
Once the GPS receiver has located its position it is usually displayed in one of two common formats:
Latitude and longitude
Universal transverse mercator (UTM).
Latitude and Longitude
Latitudes and longitudes are angles.
Latitude
Latitude gives the location of a place on the Earth north or south of the Equator.
Latitude is an angular measurement in degrees (marked with ) ranging from 0 at the Equator to 90 at the poles (90 N for the North Pole or 90 S for the South Pole)
Latitude--Equator
The equator divides the planet into a Northern Hemisphere and a Southern Hemisphere.
The latitude of the equator is, by definition, 0 .
Latitude--cont.
Four lines of latitude are named because of the role they play in the geometrical relationship with the Earth and the Sun.
Longitude
Longitude--cont.
The circumference of the earth at the equator is approximately 24,901.55 miles.
Longitude--cont.
There is an important difference between latitude and longitude.
The circumference of the earth declines as the latitude increase away from the equator.
This means the miles per degree of longitude changes with the latitude.
This makes determining the distance between two points identified by longitude more difficult.
Mercator Projection
A Mercator projection is a pseudocylindrical conformal projection (it preserves shape).
Points on the earth are transferred, on an angle from the center of the earth, to the surface of the cylinder.
What you often see on poster-size maps of the world is an equatorial mercator projection that has relatively little distortion along the equator, but quite a bit of distortion toward the poles.
Mercator Projection
What a transverse mercator projection does, in effect, is orient the equator north-south (through the poles), thus providing a north-south oriented swath of little distortion.
By changing slightly the orientation of the cylinder onto which the map is projected, successive swaths of relatively undistorted regions can be created.
UTM Zones
These zones begin at 180o longitude and are numbered consecutively eastward.
UTM Zones--cont.
The conterminous United States is covered by 10 UTM grid zones.
In the Northern Hemisphere each zone's northing coordinate begins at the equator as 0,000,000 and is numbered north in meters.
UTM--cont.
The UTM system uses a different grid for the polar regions.
These areas are covered by a different conformal projection called the Polar Stereographic.
Since compass directions have little meaning at the poles, one direction on the grid is arbitrarily designated "north-south" and the other "east-west" regardless of the actual compass direction.
The UTM coordinates are called "false northing" and "false easting.
Using Location Information
Determining UTM Zone
Treat west longitude as negative and east as positive.
Add 180 degrees; this converts the longitude to a number between zero and 360 degrees.
Divide by 6 and round up to the next higher number.
Example:
The location of the intersection of Hall of Fame and Virginia on OSU campus is 56 7 23.71 N and 97 05 16.079 W.
Determining a UTM Grid Value for a Map Point
The UTM grid is shown on all quadrangle maps prepared by the U.S. Geological Survey (USGS).
On 7.5-minute quadrangle maps (1:24,000 and 1:25,000 scale) and 15-minute quadrangle maps (1:50,000, 1:62,500, and standard-edition 1:63,360 scales), the UTM grid lines are indicated at intervals of 1,000 meters, either by blue ticks in the margins of the map or with full grid lines.
The 1,000-meter value of the ticks is shown for every tick or grid line.
Determining a UTM Grid Value for a Map Point--cont.
To use the UTM grid, you can place a transparent grid overlay on the map to subdivide the grid, or you can draw lines on the map connecting corresponding ticks on opposite edges.
The distances can be measured in meters at the map scale between any map point and the nearest grid lines to the south and west.
The northing of the point is the value of the nearest grid line south of it plus its distance north of that line; its easting is the value of the nearest grid line west of it plus its distance east of that line.
Determining Distance Using UTM
In the illustration the UTM coordinates for two points are given.
The distance can be determined using Pythagorean Theorem because UTM is a grid system.
UTM Example--cont.
Subtracting the easting proved the length of the horizontal side: 208,000 meters.
Subtracting the northing proves the length of the vertical side: 535,000 meters.
The distance between the two points is:
GPS Errors
Noise
Biases
Blunder
Clock
Noise Error
Noise errors are the combined effect of code noise (around 1 meter) and noise within the receiver noise (around 1 meter).
Bias Error
Selective Availability (SA)
SA is the intentional degradation of the SPS signals by a time varying bias. SA is controlled by the DOD to limit accuracy for non-U. S. military and government users.
Selective availability is turned off.
Ephemeris data errors: 1 meter
Satellite orbits are constantly changing. Any error in satellite position will result in an error for the receiver position.
SV clock errors uncorrected by Control Segment can result in one meter errors.
Tropospheric delays: 1 meter.
The troposphere is the lower part (ground level to from 8 to 13 km) of the atmosphere that experiences the changes in temperature, pressure, and humidity associated with weather changes.
Complex models of tropospheric delay require estimates or measurements of these parameters.
Bias Error--cont.
Unmodeled ionosphere delays: 10 meters.
The ionosphere is the layer of the atmosphere from 50 to 500 km that consists of ionized air. The transmitted model can only remove about half of the possible 70 ns of delay leaving a ten meter un-modeled residual.
Multipath: 0.5 meters.
Multipath is caused by reflected signals from surfaces near the receiver that can either interfere with or be mistaken for the signal that follows the straight line path from the satellite.
Blunder
Blunders can result in errors of hundred of kilometers.
Control segment mistakes due to computer or human error can cause errors from one meter to hundreds of kilometers.
User mistakes, including incorrect geodetic datum selection, can cause errors from 1 to hundreds of meters.
Receiver errors from software or hardware failures can cause blunder errors of any size.

sharunsnkk89 · 10-04-2017, 09:37 PM

[attachment=7766]

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.

subhanshu · 10-04-2017, 09:37 PM

[attachment=15498]
ABSTRACT
Where am I? Where am I going? Where are you? What is the best way to get there? When will I get there? GPS technology can answer all these questions. GPS satellite can show you exact position on the earth any time, in any weather, no matter where you are! GPS technology has made an impact
On navigation and positioning needs with the use of satellites and ground stations the ability to track aircrafts, cars, cell phones, boats and even individuals has become a reality.
This paper describes the Global positioning system (GPS) satellite. It depicts what GPS satellite is, how it works and its tracking features. This paper also gives how
the GPS satellite has been used to compute position and time, gives the details of various
segments in which the GPS system is useful. The paper gives the benefits of GPS satellite such as ability to track an object, due to reduced cost it is more affordable for everyone and helps you to find out where you are and how to get to your destination,
where ever you are going on land or sea.,
Applications such as military, car alarms, home security and home monitoring
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 cumbersome. Over the years all kinds of technologies have tried to simplify the task but everyone has had some disadvantages. Finally, the U.S. Department of Defense decided that the military had to have a super precise form of worldwide positioning. And fortunately they had the kind of money ($12 billion!) it took to build something really good. The result is the Global Positioning System, a system that's changed navigation forever.
GPS initially created by the U.S Defense Department for the military has later been made available to the public. GPS technology is not just a handheld help-me-find-my-way-home operation anymore. GPS is finding its way into cars, boats, planes, construction equipment, moviemaking gear, farm machinery, even laptop computers. Move over Mr. Bell, it won t be long until GPS will become as basic as the telephone.
ALL ABOUT GPS
A constellation of 24 satellites
A system of satellites, computers, and receivers that is able to determine the latitude and longitude of a receiver on Earth by calculating the time difference for signals from The Global Positioning different satellites to reach the receiver. System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations. GPS uses these "man-made stars" as reference points to calculate positions accurate to a matter of meters. In fact, with advanced forms of GPS you can make measurements to better than a centimeter! In a sense it's like giving every square meter on the planet a unique address. GPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical. And that makes the technology accessible to virtually everyone.
Technical description
The system consists of a "constellation" of at least 24 satellites in 6 orbital planes. The GPS satellites were initially manufactured by Rockwell; the first was launched in February 1978, and the most recent was launched November 6 2004. Each satellite circles the Earth twice every day at an altitude of 20,200 kilometers (12,600 miles). The satellites carry atomic clocks and constantly broadcast the precise time according to their own clock, along with administrative information including the Orbital elements of their own motion, as determined by a set of ground-based observatories.
The receiver does not need a precise clock, but does need to have a clock with good short-term stability and receive signals from four satellites in order to find its own latitude, longitude, elevation, and the precise time. The receiver computes the distance to each of the four satellites from the difference between local time and the time the satellite signals were sent (this distance is called a pseudo range). It then decodes the satellites' locations from their radio signals and an internal database. The receiver should now be located at the intersection of four spheres, one around each satellite, with a radius equal to the time delay between the satellite and the receiver multiplied by the speed of the radio signals. The receiver does not have a very precise clock and thus cannot know the time delays. However, it can measure with high precision the differences between the times when the various messages were received. This yields 3 hyperboloids of revolution of two sheets, whose intersection point gives the precise location of the receiver. This is why at least four satellites are needed: fewer than 4 satellites yield 2 hyperboloids, whose intersection is a curve; it is impossible to know where the receiver is located along the curve without supplemental information, such as elevation. If elevation information is already known, only signals from three satellites are needed (the point is then defined as the intersection of two hyperboloids and an ellipsoid representing the Earth at this altitude). The receiver contains a mathematical model to account for these influences, and the satellites also broadcast some related information, which helps the receiver in estimating the correct speed of propagation. High-end receiver /antenna systems make use of both L1 and L2 frequencies to aid in the determination of atmospheric delays.

hareend · 10-04-2017, 09:37 PM

[attachment=4094]
Why do we need GPS?
Trying to figure out where you are is probable man 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.

[attachment=4094]

chetan7675 · 10-04-2017, 09:37 PM

[attachment=3198]

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
Trimble s online GPS tutorial
howstuffworks.com

amol_cool · 10-04-2017, 09:37 PM

[attachment=3243]

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).

nitishrao · 10-04-2017, 09:37 PM

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:
http://en.wikipediawiki/Global_Positioning_System
Visit this page link for a report:
http://geology.isu.edu/geostac/Field_Exe...lox_en.pdf

PPT:

sujith014 · 10-04-2017, 09:37 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 :-
http://forests.tn.nicgeomatics/globalpos...ystem.html

http://gisdevelopmenttechnology/gps/techgp0038.htm

kamat_prathamesh · 10-04-2017, 09:37 PM

[attachment=7651]

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

alaapanujan · 10-04-2017, 09:37 PM