USE OF GLOBAL POSITIONING SYSTEM (GPS)IN TRANSPORTATION ENGINEERING

VINAYAK GIRISH

‘Global positioning system technology is relatively new and is considered to be a leading form of

advanced technology. GPS has found application in land transportation, civil aviation, maritime,

surveying, mining, earth science, electric power system telecommunication and outdoor recreational

activities. The objective of the paper is to explore application of GPS in traffic engineering or more

specifically in intelligent transportation system (dynamic route guidance’).

Keywords: GPS, DGPS, CONSTELLATION, TRANSPORTATION

1.0-INTRODUCTION

Transportation infrastructure represents one of the largest and most critical Investments by any

country. Movement of goods & people are vital for every aspect of country’s economy. GIS & GPS

based asset management for road and railway transportation system can improve the efficiency of

operations, at the same time can make significant contributions to safety including response to natural

and manmade disasters. As far as road transportation is considered GPS can be applied to all types of

ITS with positioning requirements. It could be effectively applied to some fields of ITS such as general

fleet operation, automatic vehicle location (AVL), dynamic route guidance etc.

2.0 HISTORY OF GPS

The idea was first introduced for the military purpose. The development work on GPS commenced

by the U.S Department Of Defense(DOD) in 1973,the.the aim was to develop an all weather 24 hour

positioning system to supply the positioning requirements for armed forces of US and its allies. Civil

use was secondary subject. This was operational in 1995 all rights of the system is for the u.s

department of defense. Now GPS found application in almost all fields of exploration, science,

engineering etc.

In recent years, differential GPS (DGPS) has been greatly facilitated by the presence of base stations

set up by the Canadian and the U.S federal government especially around harbor, waterways and

airports.

Under graduate student, Department of Civil Engineering

NSS college of Engineering palakkad-678008

3.0 WHAT IS ‘GPS CONSTALLATION’

The GPS constellation consists of 24 satellites arranged in 6 orbital planes with 4 satellites per

orbital plane. The orbits are called high orbits since they are 26,600km above earth’s surface. The

satellite constellation is designed to allow 24hour global user navigation and time determination

capability.

4.0 COMPONENTS OF GPS

The NAVSTAR system (Navigation Satellite Timing And Ranging) or GPS consists of mainly

three segments.

Space segment

User segment

Control segment

4.1 Space segment

Space segment consists of constellation of 24 satellites arranged in 6 orbital planes with 4 satellites

per orbital plane and the signals broadcast by them that aloe the users to determine the position,

velocity and time. Orbits are at 26,600km from the centre of earth. The satellites are traveling at speeds

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of 7000miles per hour which allows them to circle the earth once every 12hour. They are powered by

solar energy and are built to last about 10 years. If solar energy fails, they have backup batteries to keep

them running. They also have small rocket boosters to keep them flying in correct path. The orbits are

nearly circular and equally spaced above the equator at 60° separation, with an inclination relative to

the equator of 55°.

Basic functions of the satellites are the following

Receive and store data transmission by the control stations.

Maintain accurate time by means of several onboard atomic clocks.

Transmit information and signals to the user on two L-band frequencies.

Provide a stable platform on orbit for the L-band transmitters.

Fig 1: GPS constellation

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4.2. User segmentThe user segment consists of the user and the receiver part, which is a combination of hardware,

software and operational procedures. the components of a receiver are given below.

Antenna: used for GPS receivers to receive the signal from the source.

Radio frequency selection: this contains signal processing electronics.

Microprocessor: provided to carry out computations and to control the tracking and

measurement and also to determine the elevation of the satellites.

Control and display: enables the user to interact with the microprocessor.

Recording device: for data storage.

Power supply: batteries, main supply etc.

4.3. Control segment

The control segment does what its name implies- it controls the satellites by tracking them

and then provided them with corrected orbital and time information. There are five control stations

located around the world-four unmanned receiving stations and one master control station. The four

unmanned stations constantly receive data from the satellites and then send the information back to the

master control station. The master control station corrects the satellite data and together with two other

antenna sites sends the information to the GPS satellites.

5.0 Working of GPSGPS makes use of time of arrival (TOA) of the GPS signal to determine the position on

earth’s surface. A GPS satellite which has a known position in space sends out signal to a receiver on

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earth’s surface. The time interval known as time of propagation recorded at receiver is multiplied the

speed to give the emitter to receiver distance. By knowing the propagation time of signals broadcast

from the satellites at known locations, the receiver can determine its position by the method of space

resection.

6.0 Differential global positioning system (DGPS)

In order to provide better accuracy for the positioning, a method called differential GPS has

been developed. DGPS works by placing a GPS receiver at a known location. During its propagation

through atmosphere, there are chances for errors to occur due to atmospheric particles, builings etc.

since the reference station knows its exact location it can determine the errors in the satellite signals.

The base station calculates the actual corrections to the observed signals. With the aid of

communication links, these corrections are transmitted to the station.

Fig: 2 Differential GPS

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7.0 Applications in traffic engineering

Intelligent transportation system is an example of a GPS application. GPS is effectively applied in

the following fields.

Automatic vehicle location (AVL)

General fleet operation

Dynamic route guidance

GPS can also be used in the following fields but yet not found effective compared to other

positioning systems.

Advanced traffic management system(ATMS)

Advanced traveler information system(ATIS)

Commercial vehicle operation(CVO)

Advanced public transportation system(APTS)

7.1 General fleet operation

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General fleet operation involves using GPS information for the effective dispatch of vehicles as

well as monitoring overall fleet performance. The benefit of GPS in this is that the closest vehicle to a

dispatch point can be send to that point thus saving time and fuel. This can be used for both commercial

vehicle operation and emergency vehicle management. The accuracy required depends on the size of

fleet and total area being serviced. For interstate/intercountry fleet operations, a positioning system

with global coverage satisfies the requirement, which is fulfilled effectively by GPS.

7.2 Automatic vehicle locationAVL systems are computer based vehicle tracking system that functions by measuring real time

position of vehicle using GPS technology by determining location coordinates. The location

technologies found in AVL systems are usually one of the following.

Global positioning system

Signpost and odometer interpolation

Ground based radio such as Toranc

Dead reckoning

Among these GPS positioning system is more appropriate because the accuracy needed is of

the order of cm. In this system only the location determination component is an onboard GPS receiver.

Determination of the location of each vehicle typically involves a transmission initiated by the mobile

vehicle. The transmission contains a position report package which includes the vehicles latitude and

longitude derived using a GPS receiver installed in the mobile vehicle. After receiving the reported

position from the mobile unit, the known route plus position information will give enough information

for the estimation of location.

7.2.1 Benefits of AVL

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Improved overall reliability service

Quicker response to disruption in service, such as Improved dispatch and operational

efficiency

vehicle failure or unexpected congestion

Information for future planning

7.3 Dynamic route guidanceThis is system using real time traffic information to assist the users traveling along the road

networks. The sensors along with GPS receiver is used for route guidance in a vehicle. The sensors

those are used for the Dynamic route guidance are the following

(A) odometer: it is a distance sensor which is mounted on the wheels

(B) magnetic compass: it measures the direction of movement of vehicle

(C) Tilt sensor: it gives information about the pitch and roll angles of the vehicle. It may include

one or more inclinometers.

(D) Gyroscope: it measures the rate of change of heading of the vehicle.

(E) Digital maps: these are used through GPS to relate mathematical coordinates of the locations

on the street segments and intersections. The stored coordinates of the map provide a means in

coordinate’s space and allow the digital map to contribute the navigation. Once the position data

is obtained from GPS, proper signals and instructions can be prepared for the position after

comparing the position about planned route. This planned route contains a sequence of road

segments stored by digitizing the map through GIS.

During its travel, at any segment contained in the planned route, the position of the vehicle is

needed to give proper guidance action. Those actions are prescribed to the driver through the display

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units. The display information may be in voice announces to warn the driver of the approaching

maneuver.

8.0 Basic modules of GPS

There are 7 basic modules in the GPStechnology.

Digital map database module

Without a map it is difficult for a traveler to explore an unfamiliar area and make

correct decisions concerning route. A map can be either digitized or vector encoded structure. Both

methods require GIS.

Positioning module

Positioning involves determining the coordinates of a vehicle on the surface of the

earth. 3 positioning technologies are most commonly used.(1)stand alone(2)satellite

based(3)terrestrial radio based. Among this dead reckoning and GPS technologies are widely used.

Map matching module

To provide drivers with proper instructions or to display the vehicle on a map in an

error free fashion, the vehicle location must be precisely known. To reduce these errors map

matching systems have been developed to match the dead reckoned position with a position

associated with a location on a route map. When dead reckoning behavior indicates that vehicle is

in a certain position on the map, the vehicle position may be adjusted to some absolute position on

the map. This will eliminate the cumulative error until next map matching step.

Route planning module

Route planning is a process that helps the drivers plan a route prior to or during

journey. Route planning can be done in two ways. (1) Multivehicle route planning (2) single vehicle

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route planning. In multivehicle route planning, a number of destination routes are being planned for a

particular road network. For a single vehicle route planning, a single route is planned for a single

vehicle according to its current location and a given destination.

Route guidance module

Route guides is the process of guiding the driver along the route generated by the route

planning module. Guidance can be given before the trip or in real time. Pre-trip guidance could be

presented as a print out with turn to turn driving instructions, which include the information’s about the

turns, street names, travel distances and landmarks. In en-route guidance, turn to turn instructions are

given to a driver in real time; it is much useful but requires navigable map database, an accurate

positioning module, software and computational power.

Human machine interface module

The human machine interface is a module that provides the user with the means to

interact with the location and the devices. To develop a useful interface, a certain procedure must be

followed which include the identification of requirements, determination of functions to be supported,

specification of interface type, selection of control and displays and finally designing and implementing

the interface.

Wireless communication module

Wireless data applications in ITS play a critical role in making the mobile computing a

reality. It provides relevant information to the vehicle and its occupants as well as data for

transportation management systems. Traffic control centers can obtain traffic and travel time

predictions and drivers can receive traffic information to help them maneuver through traffic.

9.0 Advantages of GPS

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Due to relatively high positioning accuracy, to the mm level.

The capability of determining the velocity and time, to an accuracy with respect to position.

It is an all weather system with 24 hours availability.

It is a positioning system with no uses changes that simply requires the use of relatively low

cost hardware.

Signals are available anywhere on the globe.

The position information in 3D is obtained.

10.0 Case study:

In order to demonstrate the use of GPS in route guidance, a softwere has been developed at IIT,

Roorkee. The software is developed for the route guidance which is entering century gate of IIT

Roorkee and wants to reach the department of civil engineering. At each junction, message is flashed to

user about the turns to be taken using GPS Positioning data. The ordinate of the vehicle on the route

gets stored in the microprocessor through GIS as soon as route on a digital map database is selected.

The map matching module checks the co ordinates of these points provided by GPS. If it does not

match any point, message flashed as “vehicle off the route”. Ahead of every intersection some points

are selected on the digital map database for maneuver information. When GPS data matches with the co

ordinates of these points, information is displayed as provided by the software.

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Fig 3 flowchart of the program

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Fig 4: output of the program

11.0 Economic considerations:

The cost of good GPS equipment is quite heavy (about 30 lakhs). GPS can be justified keeping in

view its usefulness.

Important companies providing GPS service

Navsync.

CES wireless technologies.

Garmin.

Some products available in market and its present costs

Roadmate 700 by megallon - Rs 70,000

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GPS map 60cs by Garmin - Rs 22,500

Magellon GPS 2000 - Rs 9,999

iQue 3600 PDA by Garmin-

I Cn 630 In- car navigator by Navman

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12.0 Conclusion:

GPS RECIEVERS AVAILABLE IN MARKET

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GPS with the use of GIS can be effectively used in transportation engineering, many researchers

are being going on the application of GPS in ITS. This is an ever going application. We can predict that

in the near future GPS will play major role in assisting ITS through GIS application.

ACKNOWLEDGEMENT

I take immense pleasure to express my sincere gratitude to Smt Uma Devi PP, Department of

Civil Engineering, for her valuable guidance and constant encouragement that she has rendered as the

guide to my seminar. I would also like to thank Prof T. Divakaran, Head of Civil engineering

department for his valuable help. I am also thankful to Dr A.K.Raji, Lecturer; Staff-in-charge of the

seminar for her assistance during the entire period of the seminar.

References:

1. Dr. Kumar P and Shaw U C, “Use of global positioning system in transportation engineering,

Indian Highways, August 2004, pp 125-136.

2. Narain A D “Intelligent transportation system: Prospects and probabilities in India”, Indian

Highways, January 1997,pp37-44.

3. “Advanced computer applications in transportation engineering (ACATE)”

Department of civil engineering, REC, Tiruchirapalli. 4. www.garmin.com

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