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Mobile Geographic Services
David Maguire
Director of Products, ESRI Inc., USA
Infocity, Madhapur, Hyderabad – 500 035
dmaguire@esri.com
David Maguire
Director of Products, ESRI Inc., USA
Infocity, Madhapur, Hyderabad – 500 035
dmaguire@esri.com
It seems that change is the only thing that is constant in the world of information and communication technologies. Just as the mainframe and minicomputers of the 1960s and 1970s, gave way to the workstations and personal computers of the 1980s and 1990s, another revolution is upon us. Stimulated by the need for an up to date geographically sensitive information, advances in hardware size, performance and power consumption, and improvements in network bandwidth, a new breed of mobile geographic applications is being developed that promise to change forever the way we use geography in home and professional life.
Mobile geographic applications are characterised by their ability to support itinerant, distributed and ubiquitous computing.
- Itinerant - providing computing capability while moving with a person, in a vehicle, or on an aircraft or ship
- Distributed -integrating functions that are performed at different places in a way that is transparent to the user
- Ubiquitous - delivering the same functionality independent of a user’s location.
Fig. 1: Key elements of mobile GIS
Geographic services
In this context a service is a server-based application that delivers data and/or processing to clients on demand. Geographic services receive requests from clients (pagers, phones, Pocket PCs, PCs, etc.) for geographic data and/or processing (e.g. make a map, geocode an address, download data for an area). The query, analysis and mapping operations are performed on the server, or in the case of more advanced clients, possible on the client as well as the server. In the either case the results are displayed on the client. The results could be a map, a list of geocoded addresses, or a data file. Services have a number of important properties: they are always available (subject to security and connectivity constraints), they can support lightweight clients, they can process multiple clients at the same time, they can scale to support large numbers of requests, by adding additional machines, and they can be maintained centrally in secure facilities by specially trained staff. An Internet web site that draws maps is an example of a simple geographic service. Service-based architectures are increasingly being used to build traditional enterprise and new mobile geographic applications.
Applications
Busy people who are frequently on the move and want to use their time efficiently are increasingly requesting access to geographically sensitive data and services. Good quality, up to date and timely geographic data and services enable a range of new mobile geographic applications. Examples include Mapping, Yellow pages , Routing , Tracking , Advertising, Variable tariffs , Data collection , Public safety, etc.
Fig. 2: ESRI ArcGIS architecture
Mobile GIS
A mobile geographic information system is not a conventional GIS modified to operate on a small computer such as a laptop. It is a system built using a fundamentally new paradigm based on the key elements shown in Figure 1.
Wireless network
Many methods of wireless communication are available for mobile geographic systems including radio communication, but commercial cellular telephone systems are increasingly preferred. The number of mobile phone users now exceeds 50% in many European and Asian countries (it is above 75% in both Finland and Norway1 ). There are several options available for low and high level communication over cellular telephone networks.
Fig. 3: ArcPad – mobile geographic software.
Telephone protocols
Throughout the world a number of different low-level telephony standards are available. The current first generation of analog mobile telephony systems were designed for voice and are poorly suited to data transfer. The Global System for Mobile Communications (GSM) adopted in many parts of the world (note, however, that the US system is different than that used in Asia and Europe) offers a maximum data transfer rate of less than 10 Kbps (Kilobits per second) today. Newer second generation (2G) systems becoming available now, such as the General Packet Radio Service (GPRS), Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA) can provide data transfer at up to about 40 Kbps. Upgrades to 2G systems, called 2.5G, promise +100 Kbps, but these will not be available until the end of 2001 in Europe and possibly even later in the US.
Fig. 4: A mobile geographic service based on ArcPad and ArcIMS
In the last few years there has been enormous hype associated with WAP (Wireless Access Protocol). The WAP specification encompasses a relative simple and compact version of XML (extended markup language) called WML (Wireless Markup Language) suitable for issuing requests to servers and returning results. WAP also supports the inclusion of wireless bitmap (WBMP) files. Thus it is possible to make requests to a geographic service from a WAP phone and return the results as display page (called a card) containing a map in the form of an embedded bitmap.
As the hardware capabilities of client devices continues to improve, software applications become more advanced, and bandwidth limitations are alleviated, greater interest will focus on using the more widely accepted HTML and XML protocols. HTML is concerned with data presentation, whereas the more extensive XML supports data content description and structuring.
Fig. 5: San Diego Real-time traffic.
Small, hand-held client device
Advancements in hardware performance have allowed the development of small, low-powered, devices suitable for mobile geographic applications. The current situation is characterized by great diversity with higher end systems offering a quarter VGA screen (320 by 240 pixels), 8-bit color (64 colors), 32 MB of RAM and a 200MHz or more processor. The choice of operating systems includes Windows CE, Palm OS, EPOC, JavaOS and Linux. Some examples of devices include.
- Pocket PC running Windows CE
- Palm PDA running Palm OS
- Smartphone running EPOC
- Pager with proprietary OS
Network-based
- Cell Global Identity: Cellular telephone systems divide geography into base station coverage areas typically of several kilometers in size, although in urban areas they can be as small as 10 m. Only the finest resolution of data is of use to mobile geographic service users.
- Uplink Time of Arrival. U-TOA measures the time it takes for signals to travel from a handset. This system supports existing as well as new equipment, but is expensive to implement because of the high cost of upgrades to all base stations. Accuracies are around 100m.
- GPS. The Global Positioning System offers the highest locational data quality. Since the removal of selective availability accuracies of better than 10 m are possible. However, there are some limitations in the use of GPS, especially the requirement for line of sight (especially a problem in urban ‘canyons’), added cost, and the time it takes to obtain a signal. Some systems may be complemented by additional GPS receivers located a fixed positions. This improves location calculation from 20-45 seconds to 1-8 seconds.
- Enhanced Observed Time Difference. E-OTD triangulates data received from base stations. This requires that the location of base stations is accuracy known and that data signals are synchronised. The accuracy of this method is estimated to be around 125m.
Fig. 6: GOMCT Tracking.
Geographic application server
A critical part of a mobile GIS is an advanced geographic application server able to provide a range of geographic services. Such a server must offer the following capabilities:
- Rich functionality: The range of applications listed earlier must be supported. At a minimum the following services must be available: high quality mapping, geographic and attribute queries, data download, gazetteer, proximity analysis (i.e. find closest object of a given type), geocoding, and routing.
- Good performance: Performance is critical for applications servers of this type because they must be able to process many requests simultaneously and potentially millions of requests per day.
- Scalability: This includes the ability to deal simultaneously with both very large data sets and very large numbers of application requests (e.g. thousands of users requesting routing across the whole US street database of 37 million streets). It must also be possible to add processing capability without interrupting operations. As a rough guideline a medium sized database is approximately 200 Mb – 1 Gb, a large data base is 1 – 10 Gb and a very large database is greater than 10 Gb.
- Extensibility: For all organizations the transition to mobile applications is very new and no one can foresee long-term future requirements. It is essential, therefore, that application servers can be extended to support new services and increased numbers of users.
- Reliability: Because geographic services need to be available 24 by 7 they must be robust and reliable. The use of commercial off the shelf technology such as standard hardware, GIS and DBMS software configurations provides this reliability.
- Standards-based: Although wireless systems are still immature and are developing rapidly, standards such as XML are beginning to emerge. Building systems based on these standards will help ensure compatibility with future systems and applications.
The final component is a geographic database containing the content that will be made available via the geographic services in the application server. Data management and high throughput for large databases is enabled by the use of commercial off the shelf relational database management systems such as DB2, Informix, Oracle or SQL Server. The same software can be used to store and manage both the geographic and associated attribute data.
ESRI Solutions
ESRI has been building GIS software for over 20 years and has been working on Internet services for the past 5 years. The heart of ESRI’s mobile geographic services is a commercial off-the-shelf solution called ArcGIS. This is an integrated family of software products designed to satisfy the needs of desktop, enterprise and distributed GIS users. The overall characteristics of the ArcGIS systems are shown in Figure 2.
ESRI offers both client-centric and server-centric mobile geographic services solutions.
Server-centric solutions
ESRI’s mobile geographic services solutions are based substantially on ArcIMS. ArcIMS is a cross platform application server that is able to perform the following functions:
- Interface to standard web servers
- Utilize many types of geographic data in files and databases
- Broker requests from many clients to provide good scalability
- Process requests for
- Mapping
- Feature streaming (sending intelligent vector objects to advanced clients)
- Geographic and attribute queries
- Geocoding
- Routing
- Data download
- Scale to support thousands of concurrent requests and millions of daily requests for services
The low-level telephony protocols described above are concerned with transferring bits of data of a network. Higher-level applications are responsible for creating these data and encoding them in a form that geographic applications, programmers and users can work with. Again.
Client-centric solutions
A second key piece of ESRI software for mobile geographic services solutions is ArcPad. This is a relatively lightweight commercial off the shelf GIS application that runs on Pocket PCs. It is a self-contained application with several important capabilities:
- Out of the box GUI
- Pen-based interface
- Symbolise multiple layer types
- Edit vector objects (points, lines and polygons)
- Edit object attributes
- Interface to a GPS receiver
- Geographic and attribute queries
- Interface to geographic services
- Customisation
In the case of the example configuration shown in Figure 4, ArcPad is responsible for map display, allowing the user to define an area of interest (e.g. by drawing a rectangle on the screen, or asking for the map to be centered at a particular point at a given scale), defining the projection the service should use, and for making an ArcXML request to the server. The server receives the ArcXML request, obtains the data from the database, renders the requested map, clips the map, converts it to a JPEG bitmap, and creates an ArcXML formatted response. When the client receives the resulting map it displays it on the screen.
Real world implementations
Real-time traffic services – these can be broadcast to a number of mobile devices in near real-time. Several organisations are already using GIS for this type of application. See for example real-time traffic conditions in San Diego with actual travel speeds:
Routing – the many uses of routing services include planning schedules for service technicians and delivery trucks, devising routes for large loads that avoid potential obstructions such as narrow bridges, and personal routing. RTSe has developed a fully automated routing service from for wireless devices called RouteWAP using ESRI’s RouteMAP IMS product: http://www.rtse.com .
Tracking or Automated Vehicle Location (AVL) – interest in fleet management services is growing fast. Applications such as m-Track (http://novovcs.com/), Air-Track AVL (www.airtrak.com/home.htm) PortaTrack by Main Course Technologies (www.gomct.com ) utilize ArcIMS taking advantage of HTML or Java client viewers to optimise the performance of many operations.
Data collection – more powerful clients are able to perform field-based data entry. In the US Pennsylvania Department of Environmental Protection uses ArcPad in conjunction with ArcIMS and ArcSDE for field-based entry of data about West Nile virus sample data. The West Nile virus is spread by chickens and other animals and can cause human fatalities. Maps showing details of sample locations are downloaded each day to a Pocket PC running ArcPad, data about samples are collected and entered into the system, and then at the end of the day the sample data are uploaded to the main database for management and analysis.
Geographic-based tariffs – setting phone tariffs offers competitive advantage to telephony companies. SignalSoft, an ESRI Business Partner, allows calls in proximity to a customer’s home or office to be billed as part of a flat fee, just as wired calls are today. Adoption of this service will stimulate the replacement of wired phone services with wireless devices. SignalSoft integrates ArcSDE and ArcView into this business-to-business (B2B) service.
These are just a few examples of many applications that are in operation today.
Conclusions
Mobile geographic services is a fast growing field of GIS. Although there is much hype associated with the technology, it is clear that even today technology are finding real business benefits in using geographic information in a mobile context. From yellow pages to routing, to data collection there are many success stories. As the technology improves especially telephone data transfer speeds with the introduction of 3G systems, things can only get better. ESRI has been building mobile geographic services for a number of years based on the well-tried and tested ArcGIS technology. Key aspects of the ArcGIS systems are the ArcIMS application services provider and ArcPad the lightweight mobile GIS client for Pocket PC devices.