HELSINKI UNIVERSITY OF TECHNOLOGY Department of Computer Science and Engineering Mari Korkea-aho Location Information in the Internet Licentiate’s thesis submitted in partial fulfillment of the requirements for the degree of Licentiate of Science in Technology Supervisor: Professor Reijo Sulonen Instructor: Helsinki 8.10.2001
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HELSINKI UNIVERSITY OF TECHNOLOGY Department of Computer Science and Engineering
Mari Korkea-aho Location Information in the Internet
Licentiate’s thesis submitted in partial fulfillment of the requirements for the degree of Licentiate of Science in Technology
Supervisor: Professor Reijo Sulonen Instructor:
Helsinki 8.10.2001
HELSINKI UNIVERSITY OF TECHNOLOGY ABSTRACT OF LICENTIATE’S THESIS
Author: Mari Korkea-aho
Title: Location Information in the Internet
Date: 8.10.2001 Number of pages: 80
Department: Department of Computer Science and Engineering
Professorship: Tik-76 Information Processing Science
Supervisor: Professor Reijo Sulonen
Instructor:
Currently many organizations are specifying different location information formats and ways of providing location information to applications in the Internet. Such organizations are e.g. Internet Engineering Task Force (IETF), Open GIS Consortium (OGC), Third Generation Partnership project (3GPP), Location Inter-operability Forum (LIF), Wireless Application Protocol Forum (WAP Forum), and World Wide Web Consortium (W3C). Each of them basically specifies a way of their own of expressing and providing location information. This causes a serious problem. It will be difficult for applications in the Internet to use different location information sources, and the location information provided to applications might have different incompatible formats.
The objective of this work is to address this problem and propose some solutions for achieving interoperability. Interoperability can be reached on the level of a common way of expressing location information and on the level of a common way of obtaining location information. This work focuses on a common way of expressing location information, since this appears to be the easiest level to reach interoperability on.
This work introduces a common location data set that can be used by applications to enable interoperability. Because of the numerous ways of expressing location information and the different location information needs of applications, it will not be enough to provide and support only one common location data set. A common way of expressing different location data sets is also needed. Some initial suggestions for the common way of expressing different location data sets is made, including a common structure and way of encoding, naming, and registering different location data sets. The location applications might need to use several location data sets, or to express the location in different ways. For this the common location payload, a container for different location data sets and associated data was designed.
In the work it is proposed to encode the common location data set, the common way of expressing location information, and the location payload in Extensible Markup Language (XML). XML enables use of standard processing tools and provides easy methods for extending location data sets. In addition, many of the existing location expressions use XML.
In order to reach location information interoperability in the Internet in the future, cooperation between different location standardization activities will be essential, as well as having one leading standardization activity to steer the work. The Internet Engineering Task Force (IETF) should preferably lead this activity, since it is the most important standardization organization for the Internet.
The formats and syntaxes presented in this thesis are proposals, and should be improved through input from the location technology community and different standardization organizations.
Tällä hetkellä monet organisaatiot määrittelevät erilaisia paikkatiedon esitysmuotoja ja tapoja joilla toimittaa paikkatietoa Internet-sovelluksille. Tällaisia organisaatioita ovat esimerkiksi Internet Engineering Task Force (IETF), Open GIS Consortium (OGC), Third Generation Partnership project (3GPP), Location Inter-operability Forum (LIF), Wireless Application Protocol Forum (WAP Forum), ja World Wide Web Consortium (W3C). Perimmiltään jokainen näistä organisaatioista määrittelee oman tapansa ilmaista ja toimittaa paikkatietoa. Tämä aiheuttaa vakavan ongelman. Internet-sovellusten voi olla vaikeata käyttää eri paikkatietolähteitä ja sovelluksille toimitettu paikkatieto voi olla yhteensopimatonta.
Tämän työn tavoitteena on käsitellä tätä ongelmaa ja ehdottaa joitakin ratkaisuja yhteensopivuuden saavuttamiseksi. Yhteensopivuus voidaan saavuttaa eri tasoilla: yhteisellä tavalla ilmaista paikkatietoa ja yhteisellä tavalla toimittaa paikkatietoa. Työssä keskitytään yhteiseen tapaan ilmaista paikkatietoa, koska tällä tasolla vaikuttaa olevan helpointa saavuttaa yhteensopivuus.
Tässä työssä ehdotetaan yhteistä paikkatietoa kuvaavaa tietojoukkoa, jota käyttäen eri sovellukset voivat saavuttaa yhteensopivuuden. Koska on olemassa lukemattomia tapoja esittää paikkatietoa ja sovellukset tarvitsevat erilaista paikkatietoa, yksi yhteinen paikkatieto-esitysjoukko ei ole riittävä. Tarvitaan myös yhteinen tapa ilmaista erilaisia paikkatietojoukkoja. Työssä tehdään joitakin alustavia ehdotuksia yhteiselle tavalle esittää erilaisia paikkatietojoukkoja. Työssä käsitellään yhteistä rakennetta ja koodaus-, nimitys- ja rekisteröintitapaa joukoille. Joskus sovellukset voivat tarvita monta eri paikkatietojoukkoa ilmaistakseen paikan, tai niiden tarvitsee ilmaista määrätty paikka eri tavoin samalla kertaa. Tätä varten luotiin yhteinen paikkatietopaketti (payload). Se on eräänlainen säiliö eri paikkatietojoukoille ja niihin liittyvälle tiedolle.
Työssä ehdotetaan että yhteinen paikkatietojoukko, yhteinen tapa esittää eri paikkatietojoukkoja, ja paikkatietopaketti ilmaistaisiin XML-kielellä (Extensible Markup Language). XML mahdollistaa standardi työkalujen käytön ja tarjoaa joustavat mahdollisuudet laajentaa paikkatietojoukkoja. Lisäksi monet nykyiset paikkatiedon esitysmuodot käyttävät XML-kieltä.
Paikkatiedon yhteensopivuuden saavuttamiseksi tulevaisuudessa Internetissä tarvitaan yhteistyötä paikkatietoa koskevien standardointihankkeiden välillä. Sen lisäksi tarvitaan yksi johtava standardointihanke ohjaamaan työtä. Hanke tulisi mieluiten olla Internet Engineering Task Forcen (IETF:n) johtama, sillä tämä on Internetin kehitystä johtava standardointiorganisaatio.
Tässä työssä esitetyt ilmaisutavat ja syntaksit ovat ehdotuksia, ja niitä tulisi parantaa paikkatietoyhteisön ja eri standardointiorganisaatioiden palautteen perusteella.
APPENDIX A - LIST OF PUBLICATIONS.........................................................80
1. Introduction 1
Location Information in the Internet
1. INTRODUCTION
Due to the increasing availability of positioning technologies for determining
the physical location of objects and persons, the interest in different kinds of
services that make use of location information has grown rapidly. One factor
furthering this development is the E-911 mandate in the US, stating that from
October 2001 mobile phone subscribers calling the emergency number must be
locatable. This has led to the development of positioning methods in the mobile
networks. Another reason for the increasing interest is the large potential
identified for services providing or using location information. It will be possible
to create many new types of services, leading to new potential sources of
revenue, and new possibilities of attracting and retaining customers.
The increasing availability of location information has awakened the
opportunity for many new services also in the Internet, e.g. in the areas of
tracking, local information, guidance and navigation, access authorization,
resource announcement and discovery, billing, and network management. In
order to work, the location information of the object or person being positioned
needs to be provided to the service application.
Currently several organizations, standardization bodies, industry consortiums
and vendors are working on location-related technologies, and on how to
express and provide location information to applications in the Internet. Such
organizations are e.g. Internet Engineering Task Force (IETF), Open GIS
Consortium (OGC), Third Generation Partnership project (3GPP), Location
Inter-operability Forum (LIF), Wireless Application Protocol Forum (WAP
Forum), and World Wide Web Consortium (W3C). The reason for many
different activities is that the different organizations are working on these
matters from the perspective of their field of technology and their specific needs.
Another reason is that everybody wants to cover the field, because of the large
potential identified for services providing or using location information.
Each of the different activities basically specifies a way of its own of providing
and expressing location information to applications in the Internet. This creates
a serious disadvantage. The location information provided to the applications
might have different incompatible formats, and there might be different
1. Introduction 2
Location Information in the Internet
incompatible ways for applications to obtain location information from different
location information sources. This means that the various location information
formats, sources, and applications will not be interoperable in the Internet.
1.1 Objective and Scope
The objective of this work is to address the current situation of interoperability
of location information in the Internet, and propose how the problem can be
overcome by providing common ways of expressing and obtaining location
information to applications in the Internet.
The main focus will be on interoperability through a common way of expressing
location information, and on different ways of tackling this. A common way of
expressing location information appears to be the first thing to tackle, since it
enables interoperability independently of used transfer method, and it is the
easiest level to deploy by different standardization activities. The issues of a
common way of obtaining location information to applications in the Internet will
be only briefly addressed.
The work summarizes ideas gathered in several location-related activities at
Nokia Research Center during the period of May 1998 – May 2001. The author
was among the initiators of the Internet Engineering Task Force (IETF) Spatial
Location Protocol (SLoP) activity in January 2000. The goal of the activity was
to enable a common standard way for obtaining location information in the
Internet. The ideas described in this thesis are mainly outcomes and results of
this activity. The author has also participated in location standardization
activities related to the WAP Forum, W3C, and Location Inter-operability Forum
(LIF).
1.2 Organization of this Thesis
This thesis is divided into two parts. Part 1 gives background information
about what location information is, how it can be expressed, how the location of
an object can be determined, how the location information can be obtained and
transferred to applications in the Internet, what kind of requirements the
applications have on the location information, and what the current situation is
regarding different location expression, interface and transfer standardization
activities.
1. Introduction 3
Location Information in the Internet
Chapter 2 explains what location information is and gives an introduction to
the numerous ways location can be expressed in. In Chapter 3 different
methods for positioning objects are presented. Chapter 4 presents different
types of applications needing location information, how the location information
can be provided to them, and their requirements on the location information.
Chapter 5 introduces some possible interfaces for obtaining the location
information. Then different existing location information standardization
activities somehow relating to the Internet are presented in Chapter 6. After this
existing or proposed location information expressions are introduced and
analyzed in Chapter 7. Part 1 is concluded in Chapter 8 with a summary of the
current challenges caused by the different ways of expressing and providing
location information to applications in the Internet.
In Part 2 solutions for enabling interoperability are discussed. In Chapter 9
different ideas related to reaching interoperability by common ways of
expressing and obtaining location information are introduced. Chapter 10 deals
with the common way of expressing location information in the Internet,
presenting three different solution approaches: a common data set, a common
way of expressing different location data sets, and a common payload for
transporting location information. The approaches are then discussed in more
detail in the subsequent chapters. The common location data set is discussed in
Chapter 11. The requirements for such a set are presented and location data
elements needed by different applications are analyzed. After this a common
location data set is proposed. This includes the elements of the location data
set, their syntax, and encoding. Chapter 12 considers a common way of
expressing different location data sets and the requirements of such a concept,
including the naming, encoding and extendibility of data sets. In Chapter 13 the
common location payload for transferring location data sets is presented. In
Chapter 14 other important issues related to location information, including
privacy, security, billing and transformation of location information are briefly
addressed. In Chapter 15 the work is concluded and future work items
presented.
4
Location Information in the Internet
Part 1: Background
2. What is Location Information? 5
Location Information in the Internet
2. WHAT IS LOCATION INFORMATION?
A location expresses where an object is situated. The location of an object
can be expressed in many different ways. For example, the physical location of
a house can be indicated with a street address. The virtual location of a
computer in an Internet Protocol (IP)-network can be expressed by the IP-
address. This thesis focuses on expressions defining the physical location of an
object in the real world, as for example the street address above does. The
object can be a moving or stationary item, such as a person, car, dog, PC, etc.
The focus in this work is on physical objects of minor size (approx. <10 m),
whose location can be expressed as a point, independently of the object’s form
or size. This type of location will simply be called location in this work.
Sometimes the term spatial location is used to emphasize that the location is
expressed using the earth as reference frame. That is, the location is expressed
in relation to the earth.
Location information can be more than just the data expressing the location
of an object. It can also include other additional information that can be
necessary for using the location data, for improving the location measurement,
or for bringing additional value to the location data. Such information is e.g. the
velocity of the positioned object, the direction the object is moving in, the
orientation of the object, etc. The way of expressing the location information
reflects the needs of the applications it was planned for.
2.1 Location
A location is a place where an object is physically situated in the real world.
The location can be expressed in different ways using different reference
frames. It can be expressed, e.g. as absolute spatial location, descriptive
location, or relative location.
The different ways of expressing location will pinpoint the location of the
object to a certain point, area or region somewhere on or close to the earth. The
accuracy will depend on the way of expressing the location. Very often the
positioned object is considered to be a point, independently of its form or size.
This kind of location is the focus of this work. Location information is quite
challenging since a location can be expressed in so many different ways,
2. What is Location Information? 6
Location Information in the Internet
depending on the context of use and the needs of the application using the
information.
2.1.1 Absolute Spatial Location
Absolute spatial location is the location of a physical object in the world,
expressed via a 2- or 3-dimensional coordinate system in a particular spatial
reference system2. With the help of the coordinate system a specific spatial
location is converted into a set of two or three numbers, such as an x- and y-
value (and possibly a z-value). The spatial reference system expresses a 2- or
3-dimensional model of the earth and determines how the used coordinate
system is attached to the model.
2.1.1.1 Geodetic Datums
In the spatial reference system, the geodetic datum defines the size and
shape of the earth, and the origin and orientation of the coordinate system. The
shape of the earth and its surface is irregular and the different datums attempt
to model it. Since the datums describe the earth differently, the used datum will
affect e.g. how accurately one can express the position of an object, or how
exact the distance along the earth surface between two points can be
calculated. There are hundreds of different geodetic datums in use around the
world. Referencing coordinates to the wrong datum can result in position errors
of hundreds of meters.
The datums have evolved in course of time from flat- and spherical-earth
models to ellipsoidal models and complex models that completely describe the
size, shape, orientation, gravity field, and angular velocity of the earth. Flat
earth models are still used for plane surveying over distances short enough
(less than 10 km) so that the earth curvature is insignificant. Spherical earth
models represent the shape of the earth with a sphere of a specified radius.
2 The terms “coordinate system” and “spatial reference system” are used differently in different
location-related communities. When referring to a coordinate system, sometimes a coordinate
system in a specific spatial reference system is meant, sometimes again only the coordinate
system without a spatial reference system is meant. In this thesis the term is used according to
the latter definition. To indicate a combination of a certain coordinate system and a spatial
reference system the term “coordinate reference system” is used.
2. What is Location Information? 7
Location Information in the Internet
Spherical earth models are often used for short-range navigation and for global
distance approximations. Ellipsoidal earth models are used for more accurate
positioning and navigation.
One widely used datum is World Geodetic Reference System of 1984 (WGS-
84) [NIM97] specified by the United States Defense Mapping Agency. It is used
e.g. by the satellite navigation system Global Positioning System (GPS).
[Dan99b]
2.1.1.2 Coordinate Systems
The absolute spatial location can be expressed using many different
coordinate systems, for example the Latitude-Longitude-Altitude coordinate
system, the Earth Centered-Earth Fixed (ECEF) coordinate system, or the
Universal Transverse Mercator (UTM) coordinate system. The most commonly
used coordinate system today is the Latitude-Longitude-Altitude3 coordinate
system [Dan99a].
Latitude-Longitude-Altitude coordinate system
In the Latitude-Longitude-Altitude coordinate system a location is expressed
with latitude, longitude, and altitude (see Figure 1). Latitude is the north/south
Figure 1 Latitude-Longitude-Altitude coordinate system
3 Altitude is also often called height.
Pole
Equator0o Latitude
Ellipsoidsurface
Prime Meridian0o Longitude
Point P
Altitude(Height)
at Point P
a) Latitude at Point P
b) Longitude at Point P
2. What is Location Information? 8
Location Information in the Internet
component. Originally, when the earth was thought to be spherical, the latitude
was the angle between a line starting at the center of the earth and being
perpendicular to the surface of the earth and the plane of the equator.
Now that we know the earth to be ellipsoidal in shape, there are several
types of latitudes. The usual definition of latitude is the angle a line
perpendicular to the surface of the ellipsoid makes with the plane of the equator
(a, Figure 1). This is also referred to as geodetic latitude. Whenever the
unqualified term latitude is used, it is generally accepted that it refers to the
geodetic latitude. [Men01]
The longitude is the east/west component in the coordinate system. The
longitude is the angle between a reference plane (the prime meridian) and a
plane passing through the point whose location is being expressed, both planes
being perpendicular to the equatorial plane (b, Figure 1) [Dan99a]. Thus the
lines of longitude pass through the North and South Poles and intersect the
equator. The line of longitude that passes through Greenwich in England is the
most common prime meridian in use today.
Since latitude can be expressed in many different ways and there can be
different prime meridians, several latitude-longitude-altitude coordinate systems
exist. When referring to the latitude-longitude-altitude coordinate system, people
generally mean the coordinate system using geodetic latitude and the equator
and the prime meridian at Greenwich as reference planes.
The latitude and longitude are generally expressed in degrees, minutes and
seconds, or in degrees, minutes and fractional minutes, or degrees and
fractional degrees. The latitude is expressed in a range of 0-90 degrees, where
0 degrees is at the equator and 90 degrees at the North and South Poles. To
differentiate between a latitude on the northern or southern hemisphere “+” or
“N” is used to indicate northern hemisphere, and “-“ or “S” is used to indicate the
southern hemisphere. The longitude is expressed in a range of 0-180 degrees
to the west or east from the prime meridian. To express degrees to the west “+”
or “W” is used, and to express degrees to the east “-“ or “E” is used. The
altitude (or height) at a point is the distance from the reference ellipsoid to the
point in a direction normal to the reference ellipsoid. It is generally expressed in
meters.
2. What is Location Information? 9
Location Information in the Internet
Earth Centered-Earth Fixed (ECEF) coordinate system
Earth Centered, Earth Fixed coordinates (x, y, z) define a three-dimensional
position with respect to the center of mass of the reference ellipsoid (see Figure
2). The z-axis points towards the North Pole. The x-axis is defined by the
intersection of the plane defined by the prime meridian and the equatorial plane.
The y-axis is in the intersection of a plane 90 degree east of the x-axis and the
equator. [Dan99a]
Figure 2 Earth Centered-Earth Fixed (ECEF) coordinate system
Universal Transverse Mercator (UTM) coordinate system
In the Universal Transverse Mercator (UTM) coordinate system the earth is
divided into zones indicated by a number and character (see Figure 3). UTM
zone numbers designate 6 degree longitudinal strips extending from 80 degrees
south latitude to 84 degrees north latitude. UTM zone characters designate 8
degrees zones extending north and south from the equator. There are special
UTM zones between 0 degrees and 36 degrees longitude above 72 degrees
latitude and a special zone 32 between 56 and 64 degrees north latitude.
Universal Transverse Mercator (UTM) coordinates (zone, easting, and northing)
define two-dimensional horizontal positions. Each zone has a central meridian.
Eastings are measured from the central meridian with a 500 km false easting to
ensure positive coordinates. Northings are measured from the equator with a
10 000 km false northing for positions south of the equator. [Dan99a]
Pole
Equator
Ellipsoid
y
x
z
PrimeMeridian
Point (x, y, z)
2. What is Location Information? 10
Location Information in the Internet
Figure 3 Universal Transverse Mercator (UTM) zones [Dan99a]
2.1.2 Descriptive Location
Descriptive location is a location described through other means than a
coordinate system. Examples of descriptive locations are:
• Locality - a named location, e.g. “Helsinki” or “Market Square”
• Street address, e.g. “Itämerenkatu 11”
• Postal or zip code, e.g. “00100 Helsinki” or “MA 01803”
• Building number, e.g. “10 A 49”
• State or province, e.g. “Massachusetts” or “New Brunswick”
• Country - country name or code [ISO97], e.g. “Finland” or “FI”
Descriptive location is quite challenging in several ways. It can be expressed
in very many different ways, it tends to have regional differences, and it
depends on the specific human language used. There are many different
existing classifications that can be used, e.g. national postal codes, ISO country
codes [ISO97, ISO98], and Getty Thesaurus of Geographic Names [Get01].
Relative location is a specific type of descriptive location, where the location
of an object is described relative to some other object, e.g. “100 meters from the
store”, “the building next to the tower”, “close to me”, “nearest shop”, etc.
Generally, a descriptive location can be mapped to an absolute spatial location.
2. What is Location Information? 11
Location Information in the Internet
2.1.3 Transformations
The different ways of expressing location cover different needs. With the help
of different transformation rules [Dan99b] and transformation applications one
can convert between the different location formats. Converting a set of
coordinates in one spatial reference system to a set of coordinates in another
spatial reference system can generally be accomplished with acceptably small
loss of accuracy. The European Petroleum Survey Group (EPSG) [EPS01]
maintains a registry of most of the commonly used coordinate reference
systems along with the coordinate transformation parameters, which provides
the basis for the calculations [OGC00]. Each object in the registry, i.e.
coordinate reference systems and the objects needed to define them, have a
unique integer code. For example, the code for the unit meter is 9001, and the
code for the WGS-84 datum is 6326.
There is separate software that can be used for transformation between
different coordinate systems and ways of expressing location data, e.g.
EasyTrans 1.24, or FME Universal Translator5. Most of the Geographical
Information System6 (GIS) products, e.g. ArcGIS from ESRI7, also incorporate
this possibility. Open GIS Consortium is currently specifying an open interface
that enables systems to request and receive services related to coordinate
transformations [OGC00].
2.2 Other Related Data
In addition to the location of the object, there are several other parameters
that positioning methods can produce or that can be necessary for using the
location data, for improving the location measurement, or for bringing additional
value to the location data. They are, e.g., accuracy information describing the
accuracy of the position measurement, object identifiers (IDs) for identifying the
positioned object, time stamps indicating when the positioning took place or
how long a certain measurement is valid, the size and shape of the positioned
4 http://www.geoima.de/EasyTrans.html 5 http://www.safe.com/ 6 Geographical Information System is a “computer system for capturing, managing, integrating,
manipulating, analyzing and displaying data which is spatially referenced to the Earth”. 7 http://www.esri.com/
3. Positioning Methods for Determining the Location 12
Location Information in the Internet
object, the orientation of the positioned object, the velocity of the positioned
object, the direction the object is moving in, and its intended course. Besides
the location, these kinds of parameters related to the object and its location are
defined to be part of the location information.
3. POSITIONING METHODS FOR DETERMINING THE LOCATION
There are different positioning methods available for determining the location
of an object. In this chapter a brief overview will be given. Those interested in
more details can refer to the different references mentioned in the text.
3.1 Satellite Navigation Systems
Objects can be positioned with satellite navigation systems, e.g. Global
Positioning System (GPS) [Par96, Dan00] and The GLObal NAvigation Satellite
System (GLONASS) [Bör00]. The positioning in these systems is based on
measuring the distance between the receiver and the satellites by calculating
the time it takes to transmit a signal from the satellite to the receiver and the
knowledge of the position of the satellites.
When we know the position of the satellites and the distance to three
satellites we can use triangulation to calculate the 2-dimensional position
(latitude, longitude) of the receiver (see Figure 4).
Figure 4 Positioning with the help of triangulation in a satellite navigation system
S3 (x3, y3, z3)
S2 (x2, y2, z2) S1 (x1, y1, z1)
r2
rs
r1
SP1
SP3
SP2
Circle C1 on the intersection of sphere SP1 and sphere SP2
Circle C2 on the intersection of sphere SP2 and sphere SP3
P1
P2
3. Positioning Methods for Determining the Location 13
Location Information in the Internet
In Figure 4, S1, S2, S3 represent the position of the satellites. The r1 is the
calculated distance from the satellite S1 to the receiver. The receiver is located
somewhere on the sphere SP1 with the radius r1. When having the distance
measurement to satellite S2, we can narrow down the location of the receiver to
somewhere on the circle C1 where the sphere SP1 and SP2 intersect. When
having the distance to a third satellite S3 the possible positions are narrowed
down further to two points, P1 and P2, in the intersection of circle C1 and circle
C2. In order to decide which one is the true location of the receiver, a fourth
measurement could be made. But usually one of the two points is a ridiculous
answer and can be rejected without a measurement. With the distance
measurements to four or more satellites we can determine the 3-dimensional
position (latitude, longitude, altitude) of the receiver.
The Global Positioning System (GPS) is funded and controlled by the US
Department of Defense (DoD). The system was designed for military use and is
operated by the US military. However, in the 1980s, the US government made
the system available for civilian use worldwide. Earlier, there was an artificial
error (Selective Availability) introduced into the satellite data by the US DoD to
reduce the possible accuracy of a position to 100 meters for civil users. This
was removed on May 1, 2000, enabling an accuracy of about 10 meters for
civilian users [IGE00]. GPS is widely used around the world. The GLObal
NAvigation Satellite System (GLONASS) is managed for the Russian
Federation Government by the Russian Space Forces. The European Union is
currently planning a global navigation satellite system called Galileo [Gal01].
The system is planned to be developed by 2008.
3.2 Positioning in Mobile Networks
The development of positioning methods in the mobile networks, e.g. in GSM
(Global System for Mobile communications) and in UMTS (Universal Mobile
Telecommunications System), has been furthered by the Federal
Communication Commission’s (FCC) E-911 mandate in the US. The mandate
states that from October 2001 it must be possible to locate mobile phone
subscribers calling the emergency number 911 in the US [FCC99]. As a result,
positioning methods for positioning mobile phone subscribers have been
developed for different mobile networks.
3. Positioning Methods for Determining the Location 14
Location Information in the Internet
3.2.1 Positioning Methods for GSM
For GSM networks Cell Identity (CI) and Timing Advance (TA), UpLink Time
Of Arrival (UL-TOA) and Enhanced Observed Time Difference (E-OTD)
positioning methods based on measurements performed within the mobile
network, and the Assisted GPS positioning method based on GPS technology
are included in GSM standards [Ran00]. The methods will be presented in this
chapter, for more details see [Ran00, Swe01, Läh01].
CI and TA based methods were the first to be developed, since they require
no or only little changes to the mobile networks. Network infrastructure vendors
have also developed solutions incorporating some of the other mentioned
positioning methods. As a result of the E-911 amendment, especially during the
year 2001, many platforms providing positioning services have been
announced. In addition to the standardized positioning methods, different
vendors have developed proprietary positioning systems, e.g. based on CI, TA
and SIM Toolkit8.
3.2.1.1 Cell Identity and Timing Advance
The easiest way to locate a terminal in a GSM network is to use the Cell
Identity (CI), which identifies the mobile network cell that is currently serving the
mobile terminal (Figure 5). If we know the coordinates of the base station (BS)
of the network cell, the location of the terminal can be determined with the
accuracy of the size of the cell. The accuracy of this method varies depending
CI CI + TA CI Sector CI Sector + TA
Base Station
Figure 5 Different Cell Identity (CI) and Timing Advance (TA) methods
8 SIM Toolkit is a standard for value added services in GSM. Essentially, SIM Toolkit is a
client-server architecture where the SIM (Subscriber Identity Module) card in the mobile phone
acts as the gateway to the mobile network operator's server, which houses the applications. The
mobile handset is the client. [Wie01]
3. Positioning Methods for Determining the Location 15
Location Information in the Internet
on the size of the cells (approximately 50 m indoors – 35 km rural areas).
In the Cell Identity (CI) and Timing Advance (TA) method the location
measurement is improved by using Timing Advance information (Figure 5). The
Timing Advance is a parameter conceived to avoid different terminals
transmitting overlapping signal bursts to a base station during calls. It describes
how much earlier the mobile terminal needs to send its signal burst so that it
reaches the base station in time for the time slot allocated to the terminal. The
Timing Advance is proportional to the distance between the terminal and the
base station. With the help of the Timing Advance the terminal can be
positioned more exactly. Cell Sector information, i.e. the orientation and angular
width of the serving cell sector, can be used to further improve the accuracy of
the Cell Identity (CI) or the combined Cell Identity (CI) and Timing Advance (TA)
method (Figure 5).
3.2.1.2 UpLink Time of Arrival
In the UpLink Time of Arrival (UL-TOA) positioning method the Time Of
Arrival (TOA) of a known signal from a mobile terminal to at least three location
measurement units (LMUs) situated at three mobile network base stations is
measured (BS1, BS2, BS3 in Figure 6).
Figure 6 Positioning principle of the UpLink Time Of Arrival method
Time Difference of Arrival (TDOA) is calculated by subtracting pairs of TOA
values and adding the timing offset between the respective LMUs where the
TOA values were measured. The TDOA is a scaled measure of the relative
distance between the mobile terminal and the pair of base stations where the
LMUs are located, e.g. TDOA2-1=(d2-d1)/c, where c is the speed of the radio
BS1
BS2
BS3
d1
d2
d3
TDOA2-1 = = constantd2- d1
c
TDOA3-1 = = constantd3- d1
c
3. Positioning Methods for Determining the Location 16
Location Information in the Internet
waves, and d1 and d2 are the distance from the mobile terminal to the base
stations BS1 and BS2, respectively. Each TDOA measurement defines a
hyperbola (with the base stations where the TOA measurements were
conducted being at the foci of the parabola). Three such hyperbolas have a
unique intersection point. To obtain three TDOA measurements four TOA
measurements at four different measurement units (LMUs) need to be done.
However, in many cases two hyperbolas have a unique intersection and then
three TOA measurements are sufficient. In order to determine the position, the
geographical coordinates of the measurement units (LMUs) need to be known.
3.2.1.3 Enhanced Observed Time Difference (E-OTD)
The Enhanced Observed Time Difference (E-OTD) method is based on the
measured Observed Time Difference (OTD) in the mobile terminal between
arrivals of bursts from nearby pairs of base stations. Since the transmissions
from the base stations are not synchronized, Location Measurement Units
(LMUs), installed through the network in fixed and known positions, measure
Real Time Difference (RTD). If a burst is transmitted by BS1 (respectively BS2)
at the instant tTX1 (respectively tTX2) and received by the mobile terminal at the
instant tRX1 (respectively tRX2) the RTD is tTX2-tTX1 and the OTD is tRX2-tRX1. From
the OTD and RTD measurements, the Geometric Time Difference (GTD= RTD-
OTD) can be calculated. The GTD is a scaled measure of the relative distance
between the MS and a pair of base stations (BS1, BS2 in Figure 7).
Figure 7 Positioning principle of the Enhanced Observed Time Difference method
In fact GTD = RTD-OTD=(tRX1-tTX1)-(tRX2-tTX2)=(d1-d2)/c, being c the speed of
radio waves and d1=c(tRX1-tTX1), d2=c(tRX2-tTX2) the distance between the mobile
BS1
BS2
BS3
d1
d2
d3
GTD1,2 = = constantd1- d2
c
GTD1,3 = = constantd1- d3
c
3. Positioning Methods for Determining the Location 17
Location Information in the Internet
terminal and BS1, BS2 respectively. The possible positions of the mobile
terminal are located on a hyperbola having foci at BS1 and BS2. To obtain
accurate positioning, OTD and RTD measurements are needed for at least
three geographically distinct pairs of base stations.
Two variants of the E-OTD method exist: MS Assisted E-OTD and MS Based
E-OTD (MS standing for Mobile Station, i.e. the mobile terminal). In the MS
Assisted E-OTD method the mobile terminal makes the OTD measurements
and sends them for location calculation to the network. In the MS Based E-OTD
method the network broadcasts assistance data (essentially RTD values and
base stations’ coordinates) to the mobile terminal, so that it can calculate its
own position.
3.2.1.4 Assisted GPS
The idea of the assisted GPS method is to assist a GPS receiver integrated
in the mobile terminal to determine the position. Assistance data for calculating
the position is provided by stationary receivers in a GPS reference network,
which is connected to the GSM network. The advantage of these stationary
receivers is that they have clear views of the sky and can operate continuously.
[Ran00]
Different assistance data allow a reduction of receiver start-up time, an
increase of receiver sensitivity, a reduction of power consumption in the mobile
terminal, a decrease of acquisition time, and an improvement of location
accuracy. There are also proposed methods where the position is calculated in
the network instead of the mobile terminal.
3.2.2 Positioning Methods in UMTS
The UMTS standards include the methods Cell Identity, Observed Time
Difference Of Arrival-Idle Period DownLink (OTDOA-IPDL), and Assisted GPS.
The Observed Time Difference Of Arrival-Idle Period DownLink (OTDOA-IPDL)
is an adaptation of the Enhanced Observed Time Difference (E-OTD) method
(described in Section 3.2.1.3) to the UMTS system [Ran00]. The positioning
method will be deployed after the UMTS networks have been taken into public
use.
3. Positioning Methods for Determining the Location 18
Location Information in the Internet
3.2.3 Other Positioning Methods
In addition to the standardized methods, several proprietary positioning
systems have been developed, e.g. based on CI, TA and SIM Toolkit. Lists of
positioning solutions and vendors can be found at [GEO01] or [T3G01].
Positioning methods standardization is also conducted for other mobile
networks, e.g. for IS-136 Time Division Multiple Access (TDMA) widely used in
America, and IS-95 Code Division Multiple Access (CDMA) cellular systems.
For IS-95 a method called Advanced Forward Link Trilateration (AFLT) is
specified. The method is based on measuring the time of arrival of radio signals
from the base stations.
3.3 Local Positioning Systems
There are also so-called local positioning systems for indoor and local area
positioning. The systems are based on short-range communication, using e.g.
Infra-Red (IR) [ATT01, MIT99], Radio Frequency Identification (RFID) [AIM01,
WER99], Bluetooth, and Wireless Local Area Networks (WLAN). The solutions
vary depending on the used technologies. In the basic systems, objects having
unique identifiers can be located to a specific space/room, or the objects can be
informed about their current location (e.g. a room number). In the more
advanced systems, the object is positioned by measuring signal strengths or by
using triangulation.
3.4 Configuration and Manual Input upon Request
The location information of physically stationary objects can also be needed,
e.g. of IP-network routers for network optimization, of an Internet device
behaving maliciously, or of a stationary PC via which an emergency call is
made. In such stationary devices the location information can be preconfigured.
For mobile terminals the location can, in addition to being determined with some
positioning method, also be given manually by the user of the terminal upon a
request by the application needing this information.
3.5 Summary of Positioning Methods
The different positioning methods fulfill different needs, since their optimal
area of use and their accuracy differ (Table 1 gives an overview). Thus a
3. Positioning Methods for Determining the Location 19
Location Information in the Internet
specific positioning method can be the best one for a specific application (e.g.
local positioning for indoor tracking).
Positioning method
Accuracy Operational area (works best)
GPS 10 m Where GPS-signals can be received (outdoors in open areas).
CI 50 m - 35 km Mobile network (GSM) coverage area (best accuracy where network cells are dense: city centers, or indoors if indoor transceivers installed).
CI+TA 100 - 200 m Mobile network (GSM) coverage area (best accuracy where network cells are dense: city centers, or indoors if indoor transceivers installed)
UL-TOA 50 - 200 m Mobile network (GSM) coverage area (best accuracy where network cells are dense: city centers, or indoors if indoor transceivers installed).
E-OTD 50 - 200 m Mobile network (GSM) coverage area (best accuracy where network cells are dense: city centers, or indoors if indoor transceivers installed).
Assisted GPS 1 - 10 m Where GPS-signals can be received (outdoors).
Local positioning systems
1 m - area Where local positioning systems are installed (limited indoor and outdoor areas).
Configuration 1 m - region Where the position is known in advance (stationary objects).
Manual input 1 m - region Where the position can be determined by the person being positioned (position can be expressed in text: street address, region, etc.).
Table 1 Accuracy and operational areas of different positioning methods
Several positioning methods can be used in parallel for positioning the same
object. The advantage of this is that different positioning methods can
complement each other providing positioning in a wider operative area or
providing a better overall location accuracy. The usage of several positioning
methods parallel is, however, a question of added value and cost.
4. Applications Using Location Information 20
Location Information in the Internet
One highly debated issue regarding positioning is the privacy of the person
being positioned. The privacy issue is the biggest threat to the acceptance and
deployment of positioning methods and services using location information. The
common understanding is that the person being positioned should be aware of
the positioning, and in most cases (with the exception of some tracking
applications, e.g. tracking of prisoners) should be able to control who can
position and who can get access to the location information at a certain time for
what purpose. The positioning methods in the mobile networks include privacy
mechanisms. The privacy issues have been widely discussed, but there are still
many legislative and technical challenges ahead.
4. APPLICATIONS USING LOCATION INFORMATION
The applications using location information can generally be categorized as
location-based and location-dependent services. A location-based service is a
service that uses information about the location of a locatable target (e.g. a
mobile phone client). A location-dependent service is a service that is only
available within a certain geographical area. The term location service is often
used for applications that can provide location information.
The applications implementing location-based and -dependent services can
be deployed e.g. within the mobile network (GSM, UMTS, etc.), or as services
in the Internet (Figure 8). The scope of this work is services located in the
Internet and how they can obtain location information.
Figure 8 Applications implementing location-based and -dependent services can be deployed e.g. within the mobile network or the Internet
GSM, UMTS, etc.)Internet
Location-based/dependent
serviceapplication
Location-based/dependent
serviceapplication
4. Applications Using Location Information 21
Location Information in the Internet
4.1 Different Types of Applications
There are numerous different kinds of location-based and -dependent
services that can be deployed in the Internet, and also many different ways of
categorizing the different types of services. Figure 9 presents examples of
different types of location-based and -dependent services.
Figure 9 Different types of location-based and -dependent services
4.2 Service Initiation
Different types of services have different models how the service is initiated,
and how the location information is provided to the service. For the service
initiation there are three models: the user initiates the service (described as “self
initiated” in Figure 9), somebody else initiates the service (described as
“initiated by others” in Figure 9), or the user subscribes to the service (described
as “subscribed” in Figure 9).
Yellow page services:Where is
the nearest restaurant?Point-of-interest services:
Closest attractionWhat happens here today?
Information Services InformationMemorizing & AssociationAdding and storing location
information to data, e.g. html-pages, emails, Calendar entries,
photos, maps
Navigation & Guidance
Where am I?How do I get to X?(single request or
continuous navigation)
�������������� �������
��� ����������
Safety Services
�������� �����
�������������
������� ������
������� ��������
������������� ��
������ ������
Notification Services
����� ����������
��������� ����������
����� ��������
�������� ���������
������ �������� �������
���� �������
Tracking Services
Authorization and access to resources, information,
spaces according to location
Security & AuthorizationServices
Location sensitive billing
Billing Services
Network managementLocation-specific
resource management and discovery
Management Services
one time
Self initiated
Initiated by othersSubscribed
Self initiated Self initiated
Self initiated
Initiated by others Initiated by others Initiated by others
one time
periodic
periodic
one time
region
one time
one time
periodicregion
periodicregion
periodicregion
one time
periodicregion
4. Applications Using Location Information 22
Location Information in the Internet
4.3 Providing Location Information to the Applications
There are principally two ways to provide location information to the
application implementing the location-based or -dependent service in the
Internet (Figure 10). They are: (1) the client interacting with the application
provides the information with its service requests, or (2) the application asks for
the information from a location information source via an interface.
Figure 10 Different ways of providing location information to applications
In the first case, where the user provides the location information with its
service requests, the client can reside inside the Internet, i.e. be directly
connected to the Internet (e.g. a World Wide Web browser), or be outside the
Internet, i.e. connect to the Internet via a gateway translating the requests into
the right message format (e.g. Wireless Access Protocol (WAP) client) (1,
Figure 10). The client can obtain the location information via some positioning
device connected to it (e.g. GPS receiver), via preconfiguration, manual input or
some location information source being able to position the device. In the latter
case, it is also possible for the gateway to attach the location information to the
request. Possible interfaces to different location information sources will be
presented in Chapter 5.
In the “self initiated” services the location information can be provided with
the service request, or obtained by the application implementing the service
from some location information source. In the service types “initiated by others”
and “subscribed” the application implementing the service generally obtains the
location from some location information source.
Location
API
Application
Internet
Gate-way
(1)
(2)
Location
Location
4. Applications Using Location Information 23
Location Information in the Internet
4.4 Requirements on the Location Information
Common for all the service types are that they require the location
information as input either once immediately, once delayed, or several times at
certain intervals. On a general level, the services can be identified to require
two different types of input: point-like location information in some form, or a
notification that a user enters or leaves a certain region (this can of course also
be calculated from location information within the service). In Figure 9, the
location information needs of different types of services are described. The term
“one time” means that service needs the location information once, “periodic”
that the service needs periodic updates with location information, and “region”
that the service could make use of information about when the user
enters/leaves a certain region.
The kind of location information needed by a service varies depending on the
service, but most of the services can manage with absolute spatial location
information (for a more detailed discussion see Section 11.2). The required
accuracy varies for the different services. Table 2 gives some indication of
required accuracies for different services. For a detailed analysis, see e.g.
[kor01a].
Accuracy of the location
Service
Regional Weather services, general traffic alerts, regional advertisement
District (<20 km) Local news, traffic reports
< 2 km Fleet management
1 km Roadside assistance
< 200 m Locating person in emergency or needing assistance
10 - 50 m Navigation and guidance services, asset location, continuous location-based information storing
Table 2 Required location accuracy by different types of services (adapted from [Dah99])
5. Interfaces for Providing Location Information 24
Location Information in the Internet
5. INTERFACES FOR PROVIDING LOCATION INFORMATION
As presented in Section 4.3 the client interacting with the service provides
the location information to the location-based/dependent service application or
the application obtains the location information from a location information
source via an interface. Some proposed interfaces are (Figure 11):
1) Interfaces in mobile networks (GSM, UMTS, etc.) for providing the
location of a mobile terminal
2) Interfaces in mobile terminals for providing the location determined by
some external positioning device, the mobile network, or manually by the
user
3) Interfaces towards local positioning systems (e.g. IR, RFID, WLAN,
Bluetooth)
4) Interfaces in stationary devices connected to the network, e.g. IP routers,
or local PCs
Figure 11 Different possible interfaces towards positioning systems
WLAN
(4) stationary devices(2) mobile devices
(3) local positiong systems
GSM, UMTS, etc.)
(1) mobile networks
API
API
API
APIAPI
API
API
RF
Bluetooth IR
APIAPI API
API
Application
6. Standardization Activities 25
Location Information in the Internet
6. STANDARDIZATION ACTIVITIES
There are many on-going standardization activities related to location-
technologies, location information, and location interfaces in different
standardization bodies and industry consortiums. They are, among others,
European Telecommunications Standards Institute (ETSI), Third Generation
Partnership Project (3GPP), Location Inter-operability Forum (LIF), Wireless
Application Protocol Forum (WAP Forum), World Wide Web Consortium (W3C),
Internet Engineering Task Force (IETF), Open GIS Consortium (OGC),
ISO/TC211, Bluetooth Special Interest Group, Magic Service Initiative, Wireless
Location Industry Association (WLIA), and W5 Consortium (W5C). Especially
during the past year (2000-2001) many new activities were established.
There are several reasons why there are so many different standardization
activities. One reason is that there are many fields of technology to cover. Quite
a few of the activities are developing location technologies, location information,
and interfaces specific for their field of technology and its specific needs.
Another reason for so many different activities is the large potential identified for
different kinds of location services providing or using location information. The
increasing availability of location information will enable many new types of
services. This again will mean new possible sources of revenue, and new
possibilities of attracting and retaining customers. Everybody wants to
participate, in order to get a piece of the cake. This is probably the main reason
why so many new activities have been established lately. Everybody wants to
cover the field.
The objectives and scope of the different standardization activities will be
presented in the following sections. In the review our main focus will be on
standardization activities that are in some way related to the Internet. In Section
6.10 the different activities, their scopes, and possible similar objectives
between the activities are summarized.
6. Standardization Activities 26
Location Information in the Internet
6.1 ETSI and 3GPP
The European Telecommunications Standards Institute (ETSI)9 and Third
Generation Partnership Project (3GPP)10 are telecommunication
standardization organizations working on the standardization of the mobile
networks GSM and UMTS, among other things. As a result of the E-911
amendment stating that emergency calls must be locatable, they are
standardizing a location service architecture for GSM and UMTS11. The main
objective of the work is to enable positioning of mobile (phone/terminal)
subscribers in the mobile networks. The standards specify positioning methods
for positioning mobile subscribers (see Section 3.2), and an architecture with
network elements for positioning measurements, calculations, and provisioning
of location information. The architecture includes a Gateway Mobile Location
Center (GMLC) that provides the location information of mobile subscribers.
The GMLC is planned to have an interface towards the Internet. The standards
also define a location information format for expressing and transporting the
location information of a mobile subscriber within the mobile networks [3GP00].
6.2 LIF
Nokia, Ericsson, and Motorola established the Location Inter-operability
Forum12 (LIF) in September 2000. The objectives of this industry initiative are to
[LIF01]:
• Define a simple and secure access method (i.e. an application program
interface - API) for appliances and Internet applications to access location
information from the wireless networks irrespective of their underlying air
interface technologies and positioning methods.
• Promote a family of standards-based location determination methods and
their supporting architectures, which are based on Cell Sector
9 http://www.etsi.org/ 10 http://www.3gpp.org/ 11 Actually T1P1.5 subcommittee of the American telecommunications standardization
organization T1 (http://www.t1.org/) conducted part of the GSM location service standardization
work. 12 http://www.locationforum.org/
6. Standardization Activities 27
Location Information in the Internet
information, Cell Identity and Timing Advance, E-OTD (GSM), AFLT (IS-
95), and Assisted GPS (for definitions of these see Section 3.2).
• Work with industry experts and organizations to define/adopt common
solutions that facilitate billing, revenue sharing and provisioning of
location services and applications in multi-network, multi-vendor and
multi-service environments.
• Establish a framework for contributing to the global standard bodies and
specification organizations to define common methods and procedures for
the testing and verification of the LIF-recommended access method and
positioning technologies.
The API for Internet applications (called LIF-API) is being defined. It works as
an interface towards the GMLC. The on-going specification uses the interface of
Ericsson’s Mobile Positioning Center [Swe99] as basis. The LIF-API will use
XML (Extensible Markup Language) for describing location information and
service function calls, and Hypertext Transfer Protocol (HTTP) and Secure
Sockets Layer (SSL) for data transport.
6.3 WAP Forum
In the WAP Forum13, the industry consortium standardizing the Wireless
Application Protocol (WAP) technology, there is a Location Drafting Committee.
The purpose of the Location Drafting Committee is to define a WAP location
framework for enabling location-based services. Goals for the activity are to
[Zil00]:
• Define an extensible location framework architecture including the access
to position information available in the client and/or in the network
positioning entity and/or other entities.
• Define a simple, transparent and position procedure independent location
application interface.
• Address location-related privacy issues.
13 http://www.wapforum.org/
6. Standardization Activities 28
Location Information in the Internet
The messages in the location framework (location query requests and
responses) will be coded as XML documents. In the WAP location framework
latitude and longitude coordinates using the WSG-84 datum is the mandatory
location format. The WAP User Agent profile (UAProf) as described in [WAP99]
can be used to convey location capability information (e.g. the URL address of
the location information source, or the client location capabilities).
6.4 W3C
In cooperation with the WAP Forum the World Wide Web Consortium14
(W3C) arranged a workshop on Position Dependent Information Services15 in
February 2000. The workshop pointed out that a simple extendible data model
for expressing location data, the way of transporting the information (including
the protocol and architecture) to Web-applications, and privacy and security
mechanisms to protect the information need to be defined. After the workshop
there have not been any further W3C public activities in this field.
In 1999 W3C received two independent submissions describing XML-based
data representation formats that include location data. They are Point Of
Interest eXchange Language (POIX) [Kan99] and NaVigation Markup Language
(NVML) [Sek99].
6.5 IETF
At the beginning of 2000 a group of people started the Spatial Location
Protocol (SLoP) activity in the IETF16 (Internet Engineering Task Force)
[SLo00b]. The objective of the activity was to specify a common protocol
(implying also a common API) for obtaining location information in the Internet.
This means that different location sources, devices, applications, etc, connected
to the Internet would have one common way of communicating location
information [Tan00a].
Initially the work considered a general location architecture where location
information of locatable objects would be accessible on SLoP-servers in the
• Location-specific resource management and discovery
• Location-sensitive billing
• Network management
11.2.1 Absolute Spatial and Descriptive Location
The analysis showed that most of the different services primarily need
absolute spatial position as input. This is also the format that most existing
location measurement systems can provide. Thus absolute spatial position
should be included in the common data set.
Some of the services also need descriptive location such as addresses, and
regions (e.g. Helsinki, Forum shopping mall). For example, the information
services could make use of both, the information memorizing and association
services could use address information to store notes to a specific location, and
the guidance services could use address as input.
Descriptive location is generally created by manual input or via
transformation services using coordinate data as input. It is quite challenging in
several ways. It can be expressed in very many different ways, it tends to have
regional differences, it depends on the human language used, and it can be
very application specific. It is, thus, difficult to add descriptive location elements
to a common location data set.
11.2.2 Size and Shape of Positioned Object
The size and shape of the positioned object could principally be used in two
ways. Firstly, to describe the object that is positioned in order to determine what
region it is covering (e.g. in finding, guidance, notification, tracking,
authorization, resource discovery, billing, and management services). Secondly,
to indicate the region of interest or object to attach information to (in information
and information memorizing & association services).
When designing the data set, the question whether the size and shape of the
positioned object ought to be included or not was considered carefully. It was
decided that the shape and size parameters should be excluded from the
common location data set. This is because most of the positioned objects are
11. A Common Location Data Set 47
Location Information in the Internet
generally of minor size (<10 m). It is also difficult to express shapes and sizes in
a common interoperable way, and the required data structures can be complex.
11.2.3 Other Information
In addition to the position information itself, there are several other
parameters that will bring added value. Many position measurement devices
also provide accuracy and altitude information. This information will bring added
value to services, but most applications can also survive without it.
It is quite evident that it is important to attach the time of measurement to the
location information. This can be essential to the processing and management.
Other information that could bring added value to services includes the
orientation of the object, its moving direction, intended course, and speed.
11.3 The Elements of the Common Spatial Location Data Set
The proposal of a common spatial location data set is based on identified
elements important to applications, and on the available data from different
devices and interfaces. In the first proposal [Kor01a] an element for unspecified
attributes was incorporated, enabling the common spatial location data set to
include some application specific elements. The very strict syntax (parameter
name = value) was later changed, so that any content could be added as
unspecified attributes. Finally, however, the element was removed all together
in order to keep the data set unambiguous and unique [Kor01b]. This simplifies
the validation and possible transformation of the complete data set. See Section
12.5 for a discussion on extending the data set.
The common spatial location data set proposal includes the following
elements:
Coordinates and Datum (mandatory)
When reviewing the various existing interfaces and location data
representation formats, it was found that most of them support coordinates
expressed in latitude, longitude, and altitude (optional) using WGS-84 datum.
Thus it is proposed that these should be used in the common spatial location
data set, where latitude and longitude would be mandatory. In order to keep the
11. A Common Location Data Set 48
Location Information in the Internet
data set simple, no other datum or coordinate systems are supported. The
choice was made to enable the altitude to be expressed both as the altitude
above the WGS-84 reference ellipsoid and as the altitude above the mean sea
level.
Location Accuracy (optional)
Location accuracy is the estimation or measurement error of a location. The
different interfaces include different types of accuracy information. It is proposed
that the most common way to express the accuracy should be included in the
common data set, i.e. horizontal accuracy, expressed by the circle of radius
from the positioned point, and height accuracy, expressed by range from the
positioned point.
Time (mandatory)
Time is the time of a measurement/fix of the location of an object. It is an
important factor for location information. With the help of the time it is easier to
manage location information, and it enables different kinds of approximations. It
is a mandatory element.
Speed (optional)
Speed is indicated as horizontal ground and vertical speed. This expression
is chosen because many systems are able to indicate horizontal ground and
vertical speed.
Direction (optional)
Direction indicates the direction of movement. It is expressed in a 2-
dimensional (horizontal) frame indicated by the magnetic (or true) North.
Course (optional)
Course indicates the direction from the current position to a defined
destination. It is expressed in a 2-dimensional (horizontal) frame indicated by
the magnetic (or true) North.
Orientation (optional)
11. A Common Location Data Set 49
Location Information in the Internet
Orientation describes the orientation of the positioned object. Orientation is
often given with a local coordinate system as reference. Since this reference
frame can be different for different objects, it will be difficult to make a common
expression based on this. One possibility would be to attach an object type
directly indicating the used reference framework. Instead of such a solution, a
method where the orientation is expressed in a 2-dimensional (horizontal) frame
indicated by the magnetic (or true) North, and a vertical element expressed by
the angle between horizontal plane and the main axis of the object is proposed.
11.4 Syntax of the Elements in the Common Spatial Location Data Set
The way of expressing each data element in the common spatial location
data set needs to be defined. Some of the existing data formats (e.g. the
location representation format in LIF [And00]) allow different optional ways to
express the data elements and include syntax information. However, in order to
keep processing as simple as possible one single way of expression is
preferred. Table 4 summarizes the proposal.
Element Expression format and Example
Coordinates
- Latitude (mandatory) - Longitude (mandatory)
- Altitude above datum (optional)
- Altitude above mean sea level (optional)
[N|S]degree.minute.second.f, degree range [0-90], decimal fraction f in arbitrary length N60.08.00.235556 [E|W]degree.minute.second.f, degree range [0-180], decimal fraction f in arbitrary length E25.00.00 [(+)|-]x.f meter from WGS-84 datum reference ellipsoid, + above, - below, decimal fraction f in arbitrary length +12 [(+)|-]x.f meter from mean sea level, + above, - below, decimal fraction f in arbitrary length +10
by circle of radius from the positioned point in (+)x.f meter, decimal fraction f in arbitrary length 50.0 in (+)x.f meter, decimal fraction f in arbitrary length
2.5
Time [Wol97, Kuh95]
- Real time of the measurement/fix (mandatory)
YYYY-MM-DDThh:mm:ss.sTZD, where YYYY = four-digit year MM = two-digit month (01=January, etc.) DD = two-digit day of month (01 through 31) hh = two digits of hour (00 through 23) mm = two digits of minute (00 through 59) ss = two digits of second (00 through 59) s = one or more digits representing a decimal fraction of a second TZD = time zone designator (Z or +hh:mm or -hh:mm) 1999-08-15T11:16:31.0+2:00
Speed
- Ground speed (optional)
- Vertical speed (optional)
(+)x.f [ms|kmh|mph|knot], where default meter/second (ms), decimal fraction f in arbitrary length 2.0 ms (+)x.f [ms|kmh|mph|knot], where default meter/second (ms), decimal fraction f in arbitrary length 1.0 ms
Direction (optional)
Magnetic/true direction, 360 degrees from North clockwise [M|T][0-360].f degrees, where fractional degrees f in arbitrary length, M default M240
11. A Common Location Data Set 51
Location Information in the Internet
Course (optional)
Magnetic/true direction, 360 degrees from North clockwise [M|T][0-360].f degrees, where fractional degrees f in arbitrary length, M default
magnetic/true direction, 360 degrees from North clockwise [M|T][0-360].f, degrees, where fractional degrees f in arbitrary length, M default M240 [(+)|-][0-180].f degrees, where fractional degrees f in arbitrary length 0
Table 4 Syntax of the elements in the common spatial data set
A formal syntax definition using the ABNF (Augmented Backus-Naur Form)
grammar for the common spatial location data set can be found in Appendix A
in the Internet draft “Common Spatial Location Data Set” [Kor01b]. The same
draft includes, in its Appendix B, a table clarifying the allowed prefixes for the
different elements.
11.5 Encoding of the Data Elements
In order to enable interoperability, a common way of encoding the
parameters is needed. The data elements can be encoded in many different
ways, e.g. as text based attribute-value pairs, in binary, in MIME (Multipurpose
Internet Mail Extensions) [Fre96a, Fre96b, Fre96c], in XML (Extensible Markup
Language) [Bra00], or in RDF (Resource Description Framework) [Las99,
Bri00].
11.5.1 Comparing Encoding Methods
When comparing the different alternatives, XML was selected. The
advantages of XML are that the encoding is easily understandable, readable by
humans, and standard tools and parsers can be used. In addition to this, many
11. A Common Location Data Set 52
Location Information in the Internet
of the other location information proposals make use of XML (as shown in
Section 7.1.2). A possible disadvantage of using XML is that it is quite verbose.
11.5.2 Encoding with XML
In XML a DTD (Document Type Definition) can be used to ensure that XML
documents conform to a common grammar. Thus a DTD of the common data
set can be used for correct parsing and validation of an XML instance of the
data set.
The DTD does not enable very good means of defining the structure, content,
and semantics of an XML document. To solve this, the XML Working Group in
the World Wide Web Consortium (W3C) has defined the XML Schema definition
language [Fal01]. It became a recommendation in May 2001. It provides a
means of defining the structure, content, and semantics of XML documents
more precisely than a DTD. With the help of the XML Schema the constraints
on the different data elements can be expressed better (more about XML
Schema in Section 12.5.1). Since there are not many tools supporting XML
Schema yet, both a DTD and an XML Schema solution are presented for the
common location data set.
11.5.3 Comments on the Use of XML
As Heflin points out in [Hef00], a DTD (the same is true for XML Schemas)
provides a syntax for an XML document, but the semantics of a DTD are
implicit. That is, the meaning of an element in a DTD is either inferred by a
human due to the name assigned to it, is described in a natural-language
comment within the DTD, or is described in a document separate from the DTD.
Humans can then build these semantics into tools that are used to interpret or
translate the XML documents, but software tools cannot acquire these
semantics independently. Thus, an exchange of XML documents works well if
the parties involved have agreed to a DTD beforehand, but becomes
problematic when one wants to search across the entire set of DTDs or to
spontaneously integrate information from multiple sources.
This is sufficient for the presented case, since a world where location data
sets are predefined, named with a unique label (ID), and published for use by
others (if preferred) is foreseen. Generally, the interacting parties will agree in
11. A Common Location Data Set 53
Location Information in the Internet
advance what data set to use, or indicate by negotiation what data sets they
support. This means that the semantics will be preprogrammed into the tools.
11.5.3.1 XML DTD for the Common Spatial Location Data Set
The Document Type Definition (DTD) for the common spatial location data
set is presented in Table 5. The DTD is publicly available at http://www-
Table 10 car_location data set extending on the common spatial location data set
12. A Common Way of Expressing Location Data Sets 62
Location Information in the Internet
Table 11 shows an XML instance of the car_location data set. <?xml version="1.0" encoding="UTF-8"?><car:car_locationxmlns:car="http://www.hut.fi/~mkorkeaa/schemata/2001/05/08/car"xmlns:slo="http://www-nrc.nokia.com/ietf-spatial/2001/05/08/location"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.hut.fi/~mkorkeaa/schemata/2001/05/08/car http://www.hut.fi/~mkorkeaa/schemata/2001/05/08/car.xsd">