手机地图 - 应用技术.doc

Mobile map - Technology for ApplicationAymen A.SolymanDeutsche Gesellschaft Fuer Technische Zusammenarbeit(GTZ) IntroductionInformation technology is rapidly changing the use of Geographic Information Systems (GISs) from the classic desktop applications into the business service market. With the ubiquitous computing, the settings change dramatically and the classic GIS market will change drastically in the coming few years. Till mid 90抯, the architecture of GIS focused on a standalone (static) environment. This architecture has been changed to move GIS applications from workstations into mobile GIS applications.Mobile map applications is not a conventional GIS modified to operate on mobile devices,but a system build using a fundamentally new paradigm(Maguire,2001).In this paper, we will discuss the integration of XML (eXtensible Markup Language) and J2ME (Java 2 Micro Edition) to build a mobile map application running on 2.5G and 3G mobile devices such as Nokia series 60.The Characteristics of the Mobile MarketIt is important to look at the mobile market in isolation. It has specific needs that make it unlike markets for PCs or fixed domestic appliances. Five key characteristics that make it unique,according to Symbian OS perspective, these characteristics are:1. Mobile phones are both small and mobile. 2. Mobile phones are ubiquitous-they target a mass market of consumer,enterprise and profissional users. 3. Mobile phones are occasionally connected,they can be used when connected to the wireless phone network,locally to other devices or on their own. 4. The need to differentiate the products in order to innovate and compete in a fast evolving market. 5. The development platform is open to enable independent technology to develop third party applications and services.Available Knowledge and ToolsIn the past years,developers of GIS applications have to rely on the programming languages and tools that were supplied by the GIS vendors.Moving GIS to the mobile technology is a big challange, taking into consideration the special characteristics of the spatial data.Combination of XML and J2ME introduces a powerful tool for serving spatial data on mobile devices. Using XML-based data format provides an object-based data format in which each feature can be defined as an object or set of objects, independent from other features. Storing spatial data in XML formats reduces the storage size of the data and improves the performance of the application. Developing in J2ME provides flexibility to adapt many different platforms. Object-based data formats supply a spatially suited data format.Understanding Mobile Map ApplicationsTo understand the mobile map application , we need to understand what is an Application. An end-user application consists of the following components(refer to figure 1):1. A user interface (UI) where user gestures are applied and interpreted as actions. 2. Application logic which recieves the actions and may request application data from a repository. 3. A data repository (both spatial and tabular data).Figure (1):Typical end user mobile map applicationsMobile map - Technology for ApplicationThe application can then be classified as distributed or local. Distributed applications typically involve both a client component and a server component of the application,whereas a local application resides on a single device.Application development is always constrained by the target platforms capabilities.This is especially true for the ultralight J2ME platform,because developers face many difficulties related to the platforms physical limitations.These difficulties include :1. The physical screen size (96*128 to 176*208) pixel,this covers a display area (12288 to 36608) pixels. 2. Limited Input/Output capabilities. 3. Limited memory. 4. Limited processing power. 5. Intermittent network connections.These characteristics are defined in J2ME configurations(CLDC) which provide specifications for all java杄nabled mobile devices.System Application ModeThere are three mode of mobile map applications based on the connectivity.These categories are:1. Offline mode (standalone), the application and data stored locally on the compact flash card. 2. Server connected mode,only application (not always) has been installed locally,but all data comes from centralaized database stored in the server. 3. Hybrid mode,some data has been installed locally and frequently business data will be fetched from server.Each mode has its own advantage and disadvantage.Offline mode can work independently(anytime and anywhere).In this mode, All data must to be installed in advance and therfore it will not provide dynamic information.On the other hand,the connected mode might be expensive to access the application and wireless connections can occasionaly drop off due to low signal strength.Overview of the Java 2 Micro Edition PlatformJ2ME is aimed squarely at consumer devices with limited resources(memory-display size and processing power). Many such devices have no option to download and install software beyond what was manufacturing process.With the introduction of J2ME, devices no longer need to be static in nature.Like its enterprise(J2EE),desktop(J2SE) and smart card (Java Card) counterparts,the J2ME platform is a set of standard Java APIs defined through the Java Community Process (JCP) program.The J2ME ArchitectureThe J2ME architecture defines configurations, profiles and optional packages as elements for building complete Java runtime environments that meet the requirements for a broad range of devices.Configurations,are composed of a virtual machine (VM) and a minimal set of class libraries.They provide the base functionality for a particular range of devices that share similar characteristics,such as network connectivity and memory footprint.Currently there are two J2ME configurations:the Connected Limited Device Configuration (CLDC) and the Connected Device Configuration (CDC).CLDC is designed for devices with intermittent network connections,slow processors and limited memory-devices such as mobile phones, two way pagers and PDAs.Profiles,In order to provide a complete runtime environment targeted at specific device categories,configurations must be combined with a set of higher level APIs,or profiles ,that further define the application life cycle,the user interface,and access to device specific properties.The Mobile Information Device Profile (MIDP) offers the core application functionality required by mobile applications,including the user interface,network connectivity,local data storage, and application management.Combined with CLDC,MIDP provides a complete Java runtime environment that leverages the capabilities of handheld devices and minimizes both memory and power consumption.Optional Packages,The J2ME platform can be further extended by combining various optional packages with CLDC and their corresponding profiles.Created to address very specific requirements,optional packages offer standard APIs for using both existing and emerging technologies such as Bluetooth, web services,wireless messaging and database connectivity. In addition to J2MEs configurations,profiles and optional packages Figure (2) shows that applications may draw on vendor-specific interfaces when needed.These are not parts of standars J2ME,but extend or provide functionality that is specific to a given device.We can think of vendor-specific APIs as extensions to configurations and profiles.Figure (2): The organization of J2MESystem Design and ImplementationThe most important elements of successful mobile map applications is the availability of quality data content and a user interface allowing easy, accurate and quick access to that content. User interface design is a significant challenge for any mobile software development due to the limited device resources. In the design phase we focused on creating an intuitive interface based on requirements and recommendations from previous ethnographic studies on mobile applications practices and was of using information resources. 1-Database structureThe spatial and attribute data was stored in XML (eXtensible Markup Language) format.XML provides a common data exchange format, encapsulating both metadata and data. This allows different applications and database to exchange information and communicate without having to understand anything about each other.The initial task in the implementation phase was to convert the spatial data from ESRI shapefile to XML format. Each feature is stored as an object.Three types of objects have been defined:1. Point object , presents the services layer. 2. Line object, presents the streets layer. 3. Rectangle object, presents the districts boundaries.As shown in (Figure4-M2), the services layer contains more than 1500 point in eight categories (hospitals-hotels-museums-clubs-cinemas-squares-malls-landmarks).2-Functions definationsThe main functions in the application can be summerized as follows:1. Map manipulation:zoomin,zoomout and pan. 2. Identify any feature from the map and retrieve the information of the selecteed feature.This information can be text data or photo. 3. Searching for a street or point of interest by specifying name perfix or by select from a sorted list of names. 4. Clear selection of the selected feature.As shown in figure (3), the user can use the mobile cursor keys (joy-stick) to scroll the map in the four main directions (right-left-up-down).The digit keys (1-2-3-4-6-7-8-9) can be used also to scroll the map in eight directions.The * key can be used to select a feature from the map (Figure 4-M10) for example select a hotel , and the # key is used to retrieve the information about the selected feature (Figure 4-M4)(this information can be text data , photo or both).The user can search for any service point or street by specifying name prefix (Figure 4-M5).The result is a list with such prefix.By selecting any of these services, it will be marked and flashed with red color on the map. Figure (3): The Keys functions in the application3-User interface and menu hierarchyJava-enabled phone interface design is very different from the design used for PC or Internet applications. System functionalities are organized in a hierarchy of nested menu options. Figure (4) shows the cascading menu for IbnBatota application. When users select a menu option, it takes them to a submenu with another list of available options. Users continue to navigate down the menu