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Development of an application for updating 3D city models by citizens

: Chen, Z.
: Schestag, I.; Wiesmann, S.; Schilling, A.

Darmstadt, 2003, 56 S.
Darmstadt, FH, Master Thesis, 2003
Master Thesis
Fraunhofer IGD ()
VRML; location-based service; Java-3D; webservice

Location Based Services (LBS), are the ability to find the geographical location of the mobile device and provide services based on this location information. With the concept of LBS, TellMaris focuses on tourists and citizens who travel European countries, especially in a region of the Baltic Sea, and use their mobile devices to get information they need on the move. Since TellMaris project is being developed and its database has been set up by retrieving data from the Shape file, one of the next important steps is to update this 3D city models if some buildings have been changed. The application of this thesis gives users possibilities to change some parameters of the buildings. After the implementation of data updating, users can view the 3D scenes in the neighbor frame with another Java applet, or VRML model could also be created if the user wants to view it in the VRML browser.
In order to implement the development of the application in the thesis, which is about to update the 3D city model and create a 3D scene, basic Java/Java3D would be used as the programming language; some geometrical theory about handling the building information, such as calculating bounding boxes, height, triangulation, etc, is the necessary mathematical knowledge for setting up the geometrical models; Oracle 9i, as a DBMS, stores all the values of buildings and offers a safe data environment; web services let this application conveniently be used, because all users in the LAN are welcomed to visit it, even in the internet; and at last, VRML will be introduced for it can also be generated in this application.
The application consists of two part: one is the Java applet which communicates with the server, sending and getting information from the server and database; the other part is a frame which shows the 3D Scenegraph and gives a visual impression to the user. Via this application the user will eventually get any needed information about his target building, and he is also allowed to change some parameters of the building and then view it as a Java3D object or generate a VRML model for the further development. Two main methods those establish the 3D model are used here: getBuildingById method is particularly used for getting detailed information of a building, virtual renovation and updating the parameters of the building to the database. Since a building is constructed by a set of triangles which are actually faces in the database, and every face is constructed by three nodes, to get a building by Id is nothing but to select the corresponding body, faces and nodes in the respective tables. getFeaturesInRegion means that all feature inside a rectangular area are selected. To implement this method, a rectangle as an area is defined by the user and it should be passed to this method as a parameter. Then some queries, which are searching the buildings ID in this region, will be executed first. The remaining work is to do the same queries as getBuildingById and to create the features. After constructing the 3D objects, the application will create a Java3D SceneGraph then view it as a VirtualUniverse.
To make the development more popular, applet-servlet communication that is a simple web application is mainly used to build up the web services. Users interact with the application by giving their target building information into an HTML form. Once the form is submitted then the Java servlet uses JDBC to store the building information in a database. Afterwards, an updated values of parameters of the building is generated by the servlet and returned as an HTML page to the user.
Because of the limitation of time, the development in the thesis has not been perfectly completed. For example, to get a proper 3D view of different sized objects, or to build up a powerful web services is the further task for the application.