Handbook of Research on Geoinformatics - Hassan A. Karimi Part 7 potx

276

Location-Based Services

Time of Arrival (TOA): The position of

a device can be determined by measuring the

transferring-time of a signal between the device

and the COO.

Time Difference of Arrival (TDOA): Deter￾mining a more precise position information of a

device by taking advantage of a cells infrastructure

and measuring the transferring time of a device

to three or more antennas.

Ubiquitous Information Management

(UIM): A communication concept, which is

free from temporal and, in general, from spatial

constraints.

Ultra Wideband (UWB): A technology

which enables very short-range positioning in￾formation.

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Chapter XXXV

Coupling GPS and GIS

Mahbubur R. Meenar

Temple University, USA

John A. Sorrentino

Temple University, USA

Sharmin Yesmin

Temple University, USA

Copyright © 2009, IGI Global, distributing in print or electronic forms without written permission of IGI Global is prohibited.

Abstr act

Since the 1990s, the integration of GPS and GIS has become more and more popular and an industry

standard in the GIS community worldwide. The increasing availability and affordability of mobile GIS

and GPS, along with greater data accuracy and interoperability, will only ensure steady growth of this

practice in the future. This chapter provides a brief background of GPS technology and its use in GIS,

and then elaborates on the integration techniques of both technologies within their limitations. It also

highlights data processing, transfer, and maintenance issues and future trends of this integration.

INTRODUCT ION

The use of the Global Positioning System (GPS)

as a method of collecting locational data for Geo￾graphic Information Systems (GIS) is increasing

in popularity in the GIS community. GIS data is

dynamic – it changes over time, and GPS is an

effective way to track those changes (Steede-Terry,

2000). According to Environmental Systems

Research Institute (ESRI) president Jack Dan￾germond, GPS is “uniquely suited to integration

with GIS. Whether the object of concern is moving

or not, whether concern is for a certain place at

a certain time, a series of places over time, or a

place with no regard to time, GPS can measure

it, locate it, track it.” (Steede-Terry, 2000).

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Coupling GPS and GIS

Although GIS was available in the market in the

1970s, and GPS in the 1980s, it was only in the mid￾1990s that people started using GPS coupled to

GIS. The GPS technology and its analogs (Global

Navigation Satellite System or GLONASS in Rus￾sia and the proposed Galileo system in Europe)

have proven to be the most cost-effective, fastest,

and most accurate methods of providing location

information (Longley et. al, 2005; Trimble, 2002;

Taylor et. al, 2001). Organizations that maintain

GIS databases – be they local governments or oil

companies – can easily and accurately inventory

either stationary or moving things and add those

locations to their databases (Imran et. al, 2006;

Steede-Terry, 2000). Some common applications

of coupling GPS and GIS are surveying, crime

mapping, animal tracking, traffic management,

emergency management, road construction, and

vehicle navigation.

BACKGROUND

Need for GPS Data in G IS

When people try to find out where on earth they

are located, they rely on either absolute coordi￾nates with latitude and longitude information or

relative coordinates where location information is

expressed with the help of another location (Ken￾nedy, 2002). GIS maps can be created or corrected

from the features entered in the field using a GPS

receiver (Maantay and Ziegler, 2006). Thus people

can know their actual positions on earth and then

compare their locations in relation to other objects

represented in a GIS map (Thurston et. al, 2003;

Kennedy, 2002).

GIS uses mainly two types of datasets: (a)

primary, which is created by the user; and (b)

secondary, which is collected or purchased from

somewhere else. In GIS, primary data can be

created by drawing any feature based on given

dimensions, by digitizing ortho-photos, and by

analyzing survey, remote sensing, and GPS data.

Using GPS, primary data can be collected ac￾curately and quickly with a common reference

system without any drawing or digitizing opera￾tion. Once the primary data is created, it can be

distributed to others and be used as secondary

data. Before using GPS as a primary data collec￾tion tool for GIS, the users need to understand the

GPS technology and its limitations.

The GPS Technology

The GPS data can be collected from a constellation

of active satellites which continuously transmit

coded signals to receivers and receive correctional

data from monitoring stations. GPS receivers

process the signals to compute latitude, longitude,

and altitude of an object on earth (Giaglis, 2005;

Kennedy, 2002).

A method, known as triangulation, is used

to calculate the position of any feature with the

known distances from three fixed locations (Le￾tham, 2001). However, a discrepancy between

satellite and receiver timing of just 1/100th of

a second could make for a misreading of 1,860

miles (Steede-Terry, 2000). Therefore, a signal

from a fourth satellite is needed to synchronize

the time between the satellites and the receivers

(Maantay and Ziegler, 2006; Longley et. al, 2005;

Letham, 2001). To address this fact, the satellites

have been deployed in a pattern that has each one

passing over a monitoring station every twelve

hours, with at least four visible in the sky all the

times (Steede-Terry, 2000).

The United States Navigation Satellite Timing

and Ranging GPS (NAVSTAR-GPS) constella￾tion has 24 satellites with 3 spares orbiting the

earth at an altitude of about 12,600 miles (USNO

NAVSTAR GPS, 2006; Longley et. al, 2005;

Steede-Terry, 2000). The GLONASS consists of 21

satellites in 3 orbital planes, with 3 on-orbit spares

(Space and Tech, 2005). The proposed system

GALILEO will be based on a constellation of 30

satellites and ground stations (Europa, 2005).

279

Coupling GPS and GIS

The NAVSTAR-GPS has three basic segments:

(1) the space segment, which consists of the satel￾lites; (2) the control segment, which is a network

of earth-based tracking stations; and (3) the user

segment, which represents the receivers that pick

up signals from the satellites, process the signal

data, and compute the receiver’s location, height,

and time (Maantay and Ziegler, 2006; Lange and

Gilbert, 2005).

Data Limitations and Accuracy Level

Besides the timing discrepancies between the

satellites and the receivers, some other elements

that reduce the accuracy of GPS data are orbit

errors, system errors, the earth’s atmosphere,

and receiver noise (Trimble, 2002; Ramadan,

1998). With better attention to interoperability

between the GPS units, hardware, and software,

some of these errors can be minimized before

the data are used in GIS (Thurston et. al, 2003;

Kennedy, 2002).

Using a differential correction process, the

receivers can correct such errors. The Differential

GPS (DGPS) uses two receivers, one stationary

and one roving. The stationary one, known as

the base station, is placed at a precisely known

geographic point, and the roving one is carried by

the surveyor (Maantay and Ziegler, 2006; Imran

et. al, 2006; Thurston et. al, 2003; Kennedy, 2002;

Taylor et. al, 2001; Steede-Terry, 2000). The base

station sends differential correction signals to the

moving receiver.

Prior to 2000, the GPS signal data that was

available for free did not deliver horizontal po￾sitional accuracies better than 100 meters. Data

with high degree of accuracy was only available

to U.S. government agencies and to some uni￾versities. After the U.S. Department of Defense

removed the restriction in May 2000, the positional

accuracy of free satellite signal data increased to

15 meters (Maantay and Ziegler, 2006). In Sep￾tember 2002, this accuracy was further increased

to 1 to 2 meters horizontally and 2 to 3 meters

vertically using a Federal Aviation Administration

funded system known as Wide Area Augmenta￾tion System (WAAS). WAAS is available to the

public throughout most of the continental United

States (Maantay and Ziegler, 2006).

Depending on the receiver system, the DGPS

can deliver positional accuracies of 1 meter or less

and is used where high accuracy data is required

(Maantay and Ziegler, 2006; Longley et. al, 2005;

Lange and Gilbert, 2005; Taylor et. al, 2001). For

example, the surveying professionals now use

Carrier Phase Tracking, an application of DGPS,

which returns positional accuracies down to as

little as 10 centimeters (Maantay and Ziegler,

2006; Lange and Gilbert, 2005).

INTEGR AT ION OF GPS AND G IS

The coupling of GPS and GIS can be explained

by the following examples:

• A field crew can use a GPS receiver to enter

the location of a power line pole in need of

repair; show it as a point on a map displayed

on a personal digital assistant (PDA) using

software such as ArcPad from ESRI; enter

attributes of the pole; and finally transmit this

information to a central database (Maantay

and Ziegler, 2006).

• A researcher may conduct a groundwater

contamination study by collecting the co￾ordinates and other attributes of the wells

using a GPS; converting the data to GIS;

measuring the water samples taken from

the wells; and evaluating the water quality

parameters (Nas and Berktay, 2006).

There are many ways to integrate GPS data

in GIS, ranging from creating new GIS features

in the field, transferring data from GPS receiv￾ers to GIS, and conducting spatial analysis in the

field (Harrington, 2000a). More specifically, the

GPS-GIS integration can be done based on the

280

Coupling GPS and GIS

following three categories – data-focused integra￾tion, position-focused integration, and technol￾ogy-focused integration (Harrington, 2000a). In

data-focused integration, the GPS system collects

and stores data, and then later, transfers data to

a GIS. Again, data from GIS can be uploaded

to GPS for update and maintenance. The posi￾tion-focused integration consists of a complete

GPS receiver that supplies a control application

and a field device application operating on the

same device or separate devices. In the technol￾ogy-focused integration, there is no need for a

separate application of a device to control the GPS

receiver; the control is archived from any third

party software (Harrington, 2000a).

Figure 1 provides an example of a schematic

workflow process of the GPS-GIS integration by

using Trimble and ArcGIS software. In short, the

integration of GPS and GIS is primarily focused

on three areas - data acquisition, data processing

and transfer, and data maintenance.

Data Acquisition

Before collecting any data, the user needs to de￾termine what types of GPS techniques and tools

will be required for a particular accuracy require￾ment and budget. The user needs to develop or

collect a GIS base data layer with correct spatial

reference to which all new generated data will be

referenced (Lange and Gilbert, 2005).

The scale and datum of the base map are also

important. For example, a large-scale base map

should be used as a reference in a site specific

project in order to avoid data inaccuracy. While

collecting GPS data in an existing GIS, the datum

designation, the projection and coordinate system

designation, and the measurement units must be

identical (Kennedy, 2002; Steede-Terry, 2000). It

is recommended that all data should be collected

and displayed in the most up-to-date datum avail￾able (Lange and Gilbert, 2005).

The user may create a data dictionary with

the list of features and attributes to be recorded

before going to the field or on-spot. If it is created

beforehand, the table is then transferred into the

GPS data collection system. Before going to the

field, the user also needs to find out whether the

locations that will be targeted for data collection

are free from obstructions. The receivers need

a clear view of the sky and signals from at least

four satellites in order to make reliable position

measurement (Lange and Gilbert, 2005; Giaglis,

2005). In the field, the user will check satellite

availability and follow the manuals to configure

GPS receivers before starting data collection.

GIS uses point, line, and polygon features, and

the data collection methods for these features are

different from one another. A point feature (e.g.,

an electricity transmission pole) requires the user

Figure 1. Example workflow process of GPS-GIS

integration