A City Modeling and Simulation Platform Based on Google Map API

A City Modeling and Simulation Platform Based on Google Map APIPeng Fuquan1, Su Jian2,*, Weng Wenyong2, and Wang Zebing21 College of Computer Science and TechnologyZhejiang UniversityHangzhou, Chinapengfuquan@2 Lab of Digital City and Electronic ServiceZhejiang University City CollegeHangzhou, China{suj,wengwy,wangzb}@Abstract. At present, China is in the most prominent time of the social transition. At the same time, population and vehic les are increased rapidly in the urban. Social interaction and large-scale events are also happened frequently in cities. All this are making the problem of urbanization increasingly serious. In order to solve the problem caused by urbanization, city modeling has been rapid developed in recent years. This paper presents a Google map based platform for city modeling and simulation. The platform aims to ease the problem caused by urbanization. It is feasible and cost-effective to develop applications base on this platform. This paper also introduces an application based on Google map API for flex, which implements some functions, such as adding, deleting, modifying points and lines on map, and the property of markers can be dynamically formulated. And all the added data is stored in the local database. On the basis of this platform, city modelers may reduce their burden and concentrate on modeling methods.Keywords: Google map API, flex, city modelling and simulation, Google Map.1 IntroductionWith the rapid development of computer technology, space technology and the ever-changing and increasingly improved computer graphics theory, GIS(Geographic information System) technology has matured and gradually been recognized and accepted. In recent years, after the "Digital Earth" concept was proposed, GIS core technology is concerned by more governments all over the world. At present, GIS which is know for managing spatial data, is playing a increasingly important role in many areas, such as global change and monitoring, military, resource management, city planing, land management, environmental studies, disaster prediction, traffic management. And China is in a social transition. The rapid increasement in urban population, increasing social interaction, and more public activities, make public facilities, schools and other construction problems to become the foundation for survival and development of the city. In particular, some cities, such as Beijing, Shanghai, which have millions of people, have particularly prominent urbanization because of the growing floating population. In order to provide a virtual scene and a certain basis to solve these problems, city modeling has a great development.In order to make a vivid and reliable city modeling platform, it must be combined with GIStechnology. This paper is mainly to introduce a map platform based on Google map API for city modeling and simulation.2 Key T echnology Introduction2.1 Google Map API DescriptionGoogle Maps API is a Secondary Development Interface provided by Google. This API provides lots of practical tools used to deal with map (As the map on the page ), And add contents to the map through a variety of services. Google map API is a free service, and it can be used on all the non-profit web site [1].Google Maps have three forms which are traditional maps, satellite maps and hybrid maps. The traditional maps can provide guidelines for the users when they are moving and help them to find the direction directly. The Satellite maps can allow users to get the real shot aerial view of the current location and let users have immersive feeling. Combing with the use of traditional maps, it can let the users obtain more accurate sense of direction, Which is the unreachable result by the traditional GPS technology[2].Currently Google Maps has launched several API service like Maps Javascript API, Maps API for Flash, Maps Data API, Earth API, Google Static Maps API. This platform is developed based on the version of Maps API for flash. After Google has opened up its own API, the application developers can use it to provide useful and simple map services for the public.Compared with the traditional GIS development, the basic features can be describedas follows:●Map operation. Google Maps's map operation could be shifted (mouse drag) and zoomedfreely..●Pre-generated map. Map is not dynamically generated based on user's request, butpre-processed into the image pyramid, which is made into the quad tree encoding after cut storing on the server side. When the map window is shifted or zoomed, you need only download new picture to fill the new area, which take full use of the multi-threaded simultaneous downloads features of the browser. And the downloaded pictures need not to be downloaded again from server when they are accessed for the second or more times [3]..●Analysis. Google Maps can achieve some spatial analysis, such as measurement, the nearestanalysis and path analysis. Recently, Google has announced that Google Maps has already support a new feature which can help users to understand the world through the maps. This is the Google Maps Street V iew. In the Street V iew, people can wander in 360°view on the virtual city streets to watch the street scene, just like walking in the real environment.●Development costs. Google Maps API is available for free resources now. If only you applyfor a key, you can use it. It makes the secondary development much easier both from the map service and development. It enhances and it is import to extent the mapping service..●Data update. Google Maps offer map service in two ways, which are vector maps andhigh-resolution satellite images. Google updates the maps from time to time; users can enjoy the latest map information. However, based on national security and some otherconsiderations, we cannot use high-resolution real-time satellite images. Commonly, we use the Quickbird remote sensing image technology 4 years ago.2.2 T echnical Framework for FlexAdobe flex is a software development kit (SDK) released by adobe systems for the development and deployment of cross-platform rich Internet applications based on the adobe flash platform. Flex applications can be written using adobe flash builder or by using the freely available flex compiler from adobe.Application development process:.●Define an application interface using a set of pre-defined components (forms, buttons, and soon).●Arrange components into a user interface design.●Use styles and themes to define the visual design.●Add dynamic behavior (one part of the application interacting with another, for example).●Define and connect to data services as needed.3 System Architecture DescriptionThis system selected MyEclipse as the development platform. Java was used to develop the controller layer, which was used to interact with database, and flex was used to develop view layer. This system selected tomcat5.5 as the web application server. Hibernate framework was used to develop data model layer. The current popular MVC design pattern was used in this system.3.1 Integration between Flex and JavaJSP is usually used as the display language in traditional J2EE projects. With the rise of the flex, RIA(Rich Internet Applications) client brings a more cool user interface, a shorter response time, which is closer to the desktop applications.This map platform uses LCDS(LiveCycle Data Service) to integrate between flex and java. Please read the reference book about how to configure LCDS in MyEclipse.3.2 Flex Integration with Google Map APIGoogle map provides not only JavaScript interface, but also provides flex interface.It still needs three steps to develop Google map application, after you configure the environment of flex development.●Apply a key of Google map API.●Download Google map API for flash SDK.●Configure the library path of the flex project. Add map_flex_*.swc which is in the directoryof the Google map API for flash SDK to the path of flex build.3.3 Database Design OverviewThe map platform uses sql server 2000 database. PowerDesigner was used to design database.1) Database E-R diagramAccording to the project requirements, and the Google Maps API component method, the structure of database was designed as follows.There are nine tables in the E-R diagram. Because there are divided into two kinds of users which include administrator and general users, there is a user table. Because points and lines is two types of marker to be added, there are point and line tables. The names of the points and lines and their attributes both are dynamic formulated. It need three tables to manage the types of the points and lines. The next section gives detail description.Because the lines which need to be added may be constituted by a number of line segments, there is a table to store the intermediate points.2) Generation of the Dynamic tableThis system is a modeling platform, which is not confined to a particular application development. So in order to meet the demands that the attributes of the points and lines could be dynamic formulated, The program needs to creat a table dynamic.Take points for example, different kinds of points that have different properties were created in database.We added a table which describe all kinds types of points in database. It is one-tomany elationship between the type of points and the attributes of the points. For example, school has many attributes, such as name, address, scale, contact information, and so on. If the type of the point is public bicycle, the attributes are different from school's. Because different type has different attributes, we need create a table to store the attributes of different types.The point_type_detail table stores the attributes. Through the id of the point, we can know all the attributes owned by the type. And when we create the type_table, we put some SQL operation, like adding, deleting, modifing, into the table. So we can dynamic operate table more convenient.4 System Design and ImplementationThere are divided into two function modules in this system. Not only we can call the service of Google map, but also we can operate local database.4.1 Google Map API Service OverviewThe Google Maps API is regularly extended, adding new functionality and features that are often released on first. This section covers these services.3) Address InquiryIn the Google Maps API, we can use the address resolution services, to achieve the address lookup function. Address Resolution is to a physical address (eg: Zhejiang University) into a geographical location (latitude and longitude information) process [4].Use ClientGeocoder the geocode (arg [0]: String) method of address resolution can be achieved. for positioning on the map, "Zhejiang University" and its label shows [5].4) Path QueryThough the Directions object (Google map API Flash version) to add route. The program code is as follows.var dir:Directions=new Directions();dir.addEventListener(DirectionsEvent.DIRECTIONS_S UCCESS, onDirLoad);dir.addEventListener(DirectionsEvent.DIRECTIONS_FAILURE, onDirFail);dir.load("from: " + from.text + " to: " + to.text);For example, get the path from Zhejiang University to Zhejiang Gongshang University.Fig. 1. Path query on the map platform4.2 Add Points and Lines on the Map5) Customize name and attributes of Points and LinesAccording to the input, we customize the name and attributes of point and line.There are listener code for the jptype.creatpnttype(ptype). If code is called correctly, the SQL code will be constructed. Because dynamic of the table, we don't use hibernate to interact with database, and direct use JDBC to visit database. Here, take point for example, there are two tables need to be operated, which includes type table and type_detail table. All the types of the point and line is read and displayed.6) Store Points and Lines in Local DatabaseIn the Google Maps API (Flash version), we can use the Marker object to add points on the map, using the Polyline object to add a line on the map. Get the latitude and longitude on the map through monitoring the mount events. While add a point, it need to obtain a coordinate which include latitude and longitude. And while add a line, it need obtain a series of coordinates. Also all the points in the line must be saved in order to display the line when read data from database.While adding points and lines, we need to pop up a message window to facilitate user to input information of points and lines. It is worth noting here that we direct to the information window shows a custom mxml page, so InfoWindowOptions attribute is used customContent. Andwhen the attribute of customContent was used, other attributes of InfoWindowOptions will be invalid[6].public var bjWindow:InfoWindowOptions=new InfoWindowOptions();var m_content:ptAdd= new ptAdd();m_tlng=latLng;bjWindow.customContent=m_content;marker.openInfoWindow(bjWindow);Besides, user should click the the same position twice before deciding to add a line on the map. The function operated as the figure followed [7].Fig. 2. Add points and lines on the map.While save data to database, not only we need to add information to the point or line window, but also add information to the dynamically generated window, which includes properties of the selected type [8].4.3 Display Points and Lines on the MapUsers read the data from database to display points and lines on the map. Firstly, read data from database to xml file. And Google Maps API (Flash version) provides an interface for users to read xml.Then display points and lines stored in database to the map platform through reading from the xml file. So we need to implement the interface which operate xml document [9].There are five interfaces to be implemented. Save a marker in the xml document. Delete a marker in the xml document. Update a marker in the xml document. Search a marker to check whether it is in the xml document, and then read data out from the xml document.We need to implement the following function to realize the operation that reading data from xml document to display on the map [10].var xmlString:URLRequest = new URLRequest("markers.xml");var xmlLoader:URLLoader = new URLLoader(xmlString);xmlLoader.addEventListener("complete", readXml);public function readXml(event:Event):void{var markersXML:XML = new XML(event.target.data);var markers:XMLList = markersXML..marker;{var marker:XML = markers[i];var latlng:LatLng= new LatLng(t, marker.lng);var marker1:Marker=new Marker(latlng);map1.addOverlay(marker1);}4.4 Custom Map ControlsThere are two function button for users to hide or display the marker on the map more convenient, which are custom map controls by subclassing ControlBase.To create a custom control available, you need to cover ControlBase of initControlWithMap() method.Y ou need to override methods from the superclass within the calling method. In the control constructor should also be specified ControlPosition.5 SummaryThis platform provide a map for city modeling and simulation. User could create local database to complete their required functions, such as bus inquiry system. Here is not give detailed description.Besides, we can see that Google map API provides a very convenient map service develop tool. Perhaps, at present the features are simple, but it is already a good beginning. The developer can insert maps into their page freely. As for providing map service, this is a big step forward.The Chinese map data provided by Google is still relatively rough, which is not as detail as United States, and there are still many services that have not provide interface. With the further improvement of the data and more service interface to be opened, Google map API will get more attention and the city modeling platform will be more perfect.Acknowledgment. This work is funded by Zhejiang Provincial Education Department Research Project (No.Y200803064), Hangzhou Science and Technology Project (No.20080433T01).References1. Zhang, X., Shen, Q., Long, Y.: Map evaluation system and its application. Earth Information Science 11(3) (2009)2. Tian, F.: Application for Digital City Information Platform Based on Google Maps. Computer & Telecommunication 11 (2008)3. Geng, Q., Miao, L., Duan, Y., Li, J.: Research and application of Web map service system basedon Google Maps. APIJournal of China institute of Water Resources and Hydropower Research 7(1) (2009)4. The Official Google Map API documentation, /apis/maps/documentation/5. Du, J., Zhang, Z.: Study on City Information Integration Platform Based on WebGIS. Application Research of Computers 22(6) (2005)6. Sun, X., Zhao, J.: Applying Google Maps API in WEBGIS. Control & Measurement 22(19) (2006)7. Google Ride Finder, /ridefinder8. Google Earth Blog, /9. Wei, W.: Google Maps and Web application integration, /222/2111222.shtml10. Y ang, Z., Y ang, M., Weng, Y.: Flex 3 RIA Illustration and intensive practice of development. Tsinghua University Press (2009)。