Technologies for Delivering Geospatial Information on the Internet
Tony Sileo GE Smallworld 10075 Westmoor Drive, Suite #200, Westminster, CO 80021
Introduction
The Internet and the World Wide Web are popular and successful largely because they are based on fairly simple, consistent, and functionally complete standards like TCP, IP, HTTP, and HTML. Likewise, electronic mail is prevalent and useful because of standards like POP and SMTP. These standards are successful not because everybody can understand how they work (or even what the acronyms stand for), but because they have been adopted by the hardware and software vendors who provide the engines and tools that make the Internet run. It is reasonable to expect that similar standards will need to be adopted in order for geospatial information on the Internet to be as popular, successful, and useful as the Web and e-mail. This paper highlights some of the current and emerging standards that can (or do) apply to geospatial information on the Internet. Many of the standards apply to both the wired and wireless Internet, but a special focus on wireless technology is also included. This paper is not all-inclusive, nor does the author intend to indicate that the standards and technologies discussed are most likely to be successful. In fact, no attempt is made to draw conclusions about particular standards or technology. Rather, the aim is to provide education about some of the standards currently in use or under development. The only conclusion or prediction worth mentioning, which is stated here rather than at the end, is that internationally accepted standards will be critical to the widespread acceptance and use of geospatial information on the Internet. Internet Information Standards This section describes some of the key data formats and languages used to send and store information on the Internet. The particular focus is on formats and languages that can be used to describe geospatial information. Extensible Markup Language (XML) What is XML? Deregulation, restructuring, and the introduction of e-Business to traditional business marketplaces is causing industry to become keenly aware of the need to exchange data as effectively, efficiently and inexpensively as possible. This need applies to spatial data just as much as more traditional forms of business information, particularly if we would like to see geospatial information to jump out of the back-office in which it is so often isolated. XML is a relatively recent innovation that many herald as the best way to meet the electronic data transfer and storage needs of business in the Internet age. XML has emerged as a key format on the Web, particularly for Business-to-Business integration. With the widespread development of XML variants for specific B2B markets, and the improved flexibility and adaptability it offers, XML will soon replace EDI (Electronic Data Interchange) as the standard format for exchanging digital information between companies. XML also forms the basis for several geospatial data languages discussed later in this paper. XML is a universal, text-based data exchange standard. In traditional data exchange formats, such as EDI, data is defined by the position it takes in the file structure. In XML the position of the data is not important – instead, tags identify or define the data content. This is in contrast to HTML, which uses tags to describe how a document should be displayed. For example, XML tags specify that a piece of text 'is a price' or 'is a date', while HTML tags specify that a piece of text 'is bold' or 'is a heading'. XML carries the identification of each data element along with the data itself. Goals of XML:
Why XML? Most large enterprises expend significant portions of their IT budget on developing methods to transfer information between isolated systems. XML helps to solve this problem by providing a flexible, platform-independent way of transferring data over standard network protocols. Data that is being transferred between systems can be easily translated to and from a standard XML format. By providing a well-known, easy to use intermediary format, XML helps avoid the need for constantly linking different systems to each other in 'point-to-point' solutions. XML has emerged as the key technology in so-called Enterprise Application Integration (EAI) - used to link together traditionally isolated information systems, both within a single enterprise, and across an extended e-Business on the Internet. According to the Utility Industry Group (UIG): “XML holds a great deal of promise for all aspects of the utility industry. Our recommendation is that the UIG proceed with XML message standards by developing the schemas and data models necessary to implement electronic business transactions for the utility industry.” XML is license-free and vendor/platform-independent. It is supported by a growing number of individuals and organizations. There are an increasing number of tools (many are free) for editing, generating, viewing, and transforming XML. XML provides a flexible, extensible mechanism that can handle any type of information. Currently, numerous standard languages based on XML are being developed for specific industries or applications (some of these are described later in this paper). Extensible Stylesheet Language (XSL) XSL is a transformation and formatting language based on XML. XSL, developed by the World Wide Web Consortium (W3C), is used to define a style for formatting or otherwise transforming an XML document. Looked at another way, an XML document is tree-structured and can be parsed and transformed into another tree programmatically. XSL defines programmatic XML transformations. It consists of three major parts:
Geography Markup Language (GML) The OpenGIS® Consortium (OGC) has recently developed a specification for Geography Markup Language (GML). GML is an XML-based data format for the transport and storage of geographic information. GML is based on the OpenGIS “simple features” model. As with other XML variants, specific tags & attributes can be added to easily extend GML, and GML can be validated, processed and displayed using standard XML tools. Just as XML helps to clearly separate content from presentation, GML aims to separate geographic content (data) from geographic presentation (maps and diagrams). Scalable Vector Graphics (SVG) SVG is a language for describing two-dimensional vector and mixed vector/raster graphics in XML. As of early November, 2000, the SVG 1.0 specification is in “candidate recommendation” stage at the World Wide Web Consortium (W3C). The W3C first published a set of SVG requirements in October 1998. SVG plug-ins are already available for some of the common web browsers (Internet Explorer and Netscape Communicator). One interesting feature of SVG drawings is that they can be interactive and dynamic. Animations can be defined and triggered either programmatically or via a scripting language tied to user interface events. It is also very straightforward to transform GML (geographic data) into SVG (geographic data and presentation) using the XSL transformation language. Vector Markup Language (VML) VML is an earlier XML extension for vector graphics, supported by Microsoft, AutoDesk, Macromedia, and others. The draft specification was submitted to the W3C in 1998, but it has not seen widespread commercial use. VML documents can be displayed in Internet Explorer 5 or later. Safe Software’s Feature Manipulation Engine (FME) can generate VML formatted data from most commercially available GIS formats. Web Map Server (WMS) The OpenGIS Web Map Server Specification defines the request and response protocols for interaction between client applications and map servers on the World Wide Web. WMS addresses basic web-based image and vector data access, display, and manipulation capabilities. As listed in the WMS Specification, a Web Map Server can do three things:
What about Wireless? Wireless Internet devices are becoming readily available and reasonably priced. 3 rd generation (3G) wireless services will offer data speeds up to 2 Mbps using common global standards. 3G networks and devices should be commercially available in the next 6-18 months. 4 th generation (4G) services promise even higher bandwidth, but are still in conceptual stages. When this much bandwidth is available, wireless access to enterprise geospatial data will become a practical reality, creating a new realm of mobile geospatial applications. This section discusses and contrasts some of the current and proposed enabling technologies for wireless Internet access. It closes with a particular focus on extending geospatial applications to mobile users. First, here are some wireless Internet data points:
Current wireless Internet access is based on three competing communication protocols – CDMA, TDMA, and GSM. These are often referred to as the 2 nd generation (2G) of wireless communication technology. 2G wireless technology has essentially been available for decades, although widespread commercial use did not occur until the 90’s. Code Division Multiple Access (CDMA) CDMA is a "spread spectrum" technology introduced and licensed by Qualcomm. CDMA systems operate in the 800 MHz spectrum in the US, and can carry both digital voice circuits and data. This is the same as the spectrum used by the Advanced Mobile Phone Service (AMPS), which is the standard analog voice cell phone service. CDMA is 8 to 10 times the data capacity of a standard AMPS voice channel, and is also 4 to 5 times that of a GSM system. CDMA also offers enhanced privacy, improved quality, simpler system planning, better coverage characteristics, lower power requirements, and bandwidth on demand. Time Division Multiple Access (TDMA) TDMA increases the channel capacity by chopping the signal into pieces and assigning each one to a different time slot, each lasting a fraction of a second. Using TDMA, a single channel can be used to handle simultaneous phone calls. In the US, TDMA systems also share the 800 MHz spectrum with AMPS. Global System for Mobile Communications (GSM) GSM is a special type of TDMA with built-in encryption services. GSM was selected as the digital wireless communications standard in Europe, operating at 900 MHz. Some US carriers are implementing GSM at 1900 MHz, so GSM phones are incompatible between the two markets. Personal Communications Service (PCS) PCS is a term coined by the U.S. Federal Communications Commission to describe a digital, two-way, wireless telecommunications system. The FCC has licensed several companies to operate PCS systems between 1850-1990 MHz. PCS networks can use CDMA, TDMA or GSM. 3G Wireless Communication Services 3 rd Generation (3G) wireless services are based on the International Mobile Telephony-2000 (IMT-2000) specifications. IMT-2000 was adopted in May 2000 by the International Telecommunications Union (ITU) after more than 10 years of intellectual, engineering and global negotiations (at times verging on the edge of international trade wars). By June 2000, 150 countries including the EU agreed to allocate spectrum for 3G wireless networks and provide three common global frequency bands for the new high-speed services. 3G networks will offer bandwidths up to 2Mbps, enabling a new generation of advanced multimedia wireless applications. They also offer the hope of compatibility between networks running different communication protocols, such as CDMA, TDMA, and GSM. In addition, 3G networks are slated to support quality-of-service guarantees, which will enable mobile voice over IP. Of course, carriers and equipment makers of the three flavors are each pushing for their own to become IMT-2000's underlying technology. The two approaches gaining most attention are cdma2000, advocated by CDMA licensees, and wideband-CDMA (W-CDMA), advocated in several variants by GSM, TDMA and personal digital cellular operators, as well as the Universal Mobile Telecommunications System (UMTS) Forum. UMTS membership includes several hundred network operators, manufacturers and equipment vendors around the world. UMTS licenses have been awards in several European countries, field trials are underway, and commercial UMTS services will be launched during 2001. There is some uncertainty as to when 3G services will be available in different markets. According to the Strategis Group, a consulting firm in Washington, D.C, both Europe and Asia could see 3G choices as early as 2002, vs. 2004 in the U.S. Another source believes 3G service in the U.S. will become widely available by late 2001 to early 2002, and won’t arrive in Europe until a year later. Still another source says Japan is expected to be the first country to implement commercial 3G service in April 2001, with European availability at the end of 2001, and the U.S. lagging until 2003 or later. 2.5G Wireless In between offering 2G and 3G, many carriers will offer so-called “2.5G” services utilizing much faster data rates than today's networks, but not as fast as 3G. 2.5G networks will transmit data at 100 kbps or faster. These faster data rates will improve the performance of existing applications, spark the development of new applications and change price/performance ratios. This will help commercial carriers and content providers bridge the gap from 2G to 3G. One example is called Enhanced Data Rates for GSM Evolution (EDGE). Another is General Packet Radio Service (GPRS), an overlay technology for GSM networks that provides improved throughput and quality of service mechanisms. 4G Wireless And yes, there is a fourth generation already on the drawing boards. At an industry conference in September 2000, top technologists from AT&T Labs and Nortel Networks sketched out their first efforts to define fourth-generation cellular networks. Nortel's VP and Chief Technology Officer for Access Networks, Dr. Al Javed, detailed a feature list for IP-based 4G networks with data rates up to 20 Mbps. AT&T demonstrated an Asymmetric Network called 4G Access that combines existing EDGE technology for the uplink with faster wideband orthogonal frequency-division multiplexing (OFDM) for the downlink. AT&T’s goal is to speed downloading of packet data, particularly for streaming audio and video. While these 4G networks are still several years out, testing and planning are already underway as carriers anticipate an intense hunger for broadband wireless data services. Current Wireless Application Standards There are currently two popular standards for delivering Internet content to wireless devices – Wireless Application Protocol (WAP) and i-Mode. Both define compressed binary data formats and modified communication protocols specifically optimized for the low bandwidth and small screen real estate available in current mobile devices. WAP is already very popular in Europe and Asia, and is gaining popularity in the US. i-Mode is wildly successful in Japan, and may soon begin surfacing in the US. Wireless Application Protocol (WAP) Phone.com, Ericsson, Motorola and Nokia formed the Wireless Application Protocol Forum in the mid- 90’s. Their goal was to provide a worldwide open standard for delivery of Internet-based services to wireless telephones. Initial technical specifications were published in 1998. By complying with WAP specifications, wireless telephone manufacturers, network operators, content providers and application developers can provide interoperable Internet-based products and services. WAP is very similar to the combination of HTML and HTTP (the basis for the wired Web) except that it adds in one very important feature: optimization for low-bandwidth, low-memory, and low-display capability environments. WAP devices can operate on GSM, CDMA, or TDMA wireless systems. A WAP request is routed to the Internet through a WAP gateway that converts the communication protocol (to TCP/IP) as well as the data format. Data is sent to WAP devices using the Wireless Markup Language (WML), which is based on XML. The gateway converts a “deck” of WML “cards” (the WAP equivalent of HTML pages) to a compressed binary form before sending it back to the client device. Instead of continually requesting and retrieving cards, each client request results in the retrieval of an entire related deck. The client device can employ logic via embedded WMLScript (the WAP equivalent of client-side JavaScript) for intelligently processing these cards and the resultant user inputs. WAP is currently supported on a wide range of mobile devices. WAP devices use “micro-browsers”, scaled-down Internet browsers that accommodate the limited screens, keyboards and memory found on mobile phones. Several WAP-compatible micro-browsers, including Microsoft Mobile Explorer, Phone.com's UP.Browser and Qualcomm's pdQbrowser, are vying for market domination. Like their desktop counterparts, the products provide Web content in response to keyboard commands but skip most graphics to provide information on small screens. WAP is not a completely open standard, although hundreds of companies have now joined the WAP forum. Significantly, neither the World Wide Consortium (W3C) or the Internet Engineering Task Force (IETF) have published any WAP related standards. There is some disagreement about the efficiency of WAP – some sources claim it is an overspecified standard. WAP only supports 2-color images - no grayscale or color images are possible. The jury is still out on the future of WAP. Many of the features of WAP are designed specifically to overcome limitations in 2G wireless technology. As those limitations are overcome by 3G services, WAP will either evolve with the technology or become obsolete. The WAP Forum is currently working on the next version, which will likely remove some of the current limitations. i-mode i-mode is really nothing more than a simpler, although more flexible, version of WAP. i-mode leverages Web standards (cHTML, a subset of HTML) and an expanding base of 2.5G packet technology. The i-mode service was launched in mid-February 1999 by NTT DoCoMo ("anywhere" in Japanese), the mobile arm of Japanese communications giant Nippon Telegraph and Telephone Corporation (NTT). Currently, approximately one in 15 of Japan's population is an i-mode user (twice as many users as WAP has worldwide). i-mode is introducing many consumers to the Web and m-commerce, with 600 "official" i-mode sites and more than 16,000 accessible sites in total. Wireless Data Formats Content is delivered to and displayed on wireless devices using various specialized markup languages and data formats. Some of the more prevalent are:
Location Services (LS) help determine the physical location of a mobile device. This can be accomplished using various combinations of GPS chipsets, cell triangulation, and signal strength calculations. Within a few years, the ability to locate a mobile device may become a commodity service available from the network operators. In fact, legislation in the US mandates this capability for emergency 9-1-1 purposes. Motorola, Ericsson and Nokia also formed the Location Interoperability Forum (LIF, http://www.locationforum.org) to define, develop, and promote a common location services solution. Location Based Services (LBS) are consumer-focused services that are based on the ability to determine the location of mobile devices. Examples include everything from a 'Closest McDonald’s' service to a 'TrakaPet' service that locates your favorite pet by attaching a wireless device to its collar. In addition to LS, there are a multitude of other enabling services that are required for LBS, many of which deal with geospatial data. Thus developing standards to access those services is critical to the emergence of a vibrant LBS market. To that end, the OpenGIS Consortium announced an OpenLS Initiative in October 2000. It appears that OpenLS and LIF are working together to develop and recommend commercially viable standards. Evolution of Mobile Devices The current generation of mobile devices includes mobile phones, personal digital assistants and in-vehicle computers. These devices are all limited by the following characteristics:
Why Wireless? After listing all this wonderful wireless technologies, it is worth discussing why wireless access is important to GITA. When near global coverage with 3G bandwidth is available for affordable devices with high-resolution color screens, mobile access to enterprise geospatial data will become a reality. For companies with large enterprise geospatial databases and complex geospatial applications, this means mobile knowledge workers can access the latest, up-to-date map and facility data:
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