A Method for Representing Thematic Data in Three-dimensional GIS Yingjie Hu, Jianping Wu, Zhenhua Lv, Haidong Zhong, Bailang Yu * Key Laboratory of Geographic Information Science, Ministry of Education East China Normal University Shanghai 200062, China
[email protected], *Corresponding author:
[email protected] Abstract—The effective representation of thematic data in 3D GIS can not only visualize tabular data intuitively in 3D environment, but also enable users to analyze thematic data directly on 3D GIS platform, thereby facilitating the decision making process. This paper proposes a method for representing thematic data in 3D GIS. Three steps are included in the method. In the first step, user is required to input some thematic representation parameters, all of which are then automatically converted into a XML fragment. In the second step, the API of the 3D GIS platform is employed to build graphic symbols according to the representation parameters and the thematic data. In the last step, we create legend and annotations to accurately interpret the meanings of the graphic symbols to user. This method has also been implemented as a module in a 3D GIS project named Digital Chongming Island, and the census data of Chongming Island are effectively represented in 3D environment. Keywords-thematic representation; symbolization; 3D GIS;
I.
Many 3D GIS products, such as Google Earth, World Wind and Skyline, have been mainly focusing on displaying 3D scene (including 3D models and satellite images) vividly and smoothly [7][8][9], but they are actually unable to represent thematic data effectively in 3D environment. Under such circumstance, users are unable to do certain data analysis directly on the 3D GIS platform and their working efficiency is consequently decreased. Fortunately, most of these 3D GIS products have provided Application Programming Interface (API) which allows users to extend the system’s functions. By employing these interfaces, we have developed a method for representing thematic data in 3D GIS. In the following sections, we first describe the method in detail and then present its implementation in a 3D GIS project named Digital Chongming Island (DCI), Shanghai, China. In the last section, we will summarize this research and draw some conclusions.
INTRODUCTION
Three-dimensional (3D) GIS, a product combing the technologies of Geographic Information System and visual reality, has been widely used in many fields nowadays. Compared with traditional flat maps, 3D GIS can visualize spatial data in a manner which is more close to the real world, thereby making full use of human’s highly developed recognition skills and helping users understand the meanings of the data thoroughly[1][2]. Moreover, by providing some powerful 3D spatial analysis functions (e.g. space-distance measurement), 3D GIS effectively facilitates the knowledge discovery process [3]. However, since 3D GIS is still in the phase of development, several important functions are waiting to be extended, and representing thematic data in 3D GIS is one of those. Representing thematic data in 3D GIS is using special graphic symbols (e.g. charts) to visualize the information of a particular subject (e.g. population) in a 3D environment. Since graphical representation is generally more intuitive than tabular data, users can easily comprehend the meanings of the data from these graphic symbols [4]. In addition, the thematic representation conforms to the well-defined and accepted cartographic conventions and therefore can accurately convey the data’s specific information to user [5][6].
This research is sponsored by the Science and Technology Commission of Shanghai Municipality (Grant No. 07DZ12037).
II.
METHOD
Our method for representing thematic data in 3D GIS contains three steps: processing thematic representation parameters, building graphic symbols, and creating legends and annotations. A.
Processing Thematic Representation Parameters This method needs user to input several parameters that are used to regulate the way in which the thematic data will be represented. Such parameters include the source of the thematic data (e.g. the target fieldname of a layer), the symbolization approach (unique values, graduated colors, graduated symbols, or charts), the specific colors and transparencies of the symbols, and some other parameters (e.g. the number of the classes if the user needs to represent thematic data in the form of graduated colors). In order to enable this method to function on both desktop and web-based 3D GIS platforms, we then convert these parameters into a XML fragment which can be easily transmitted and received on the Internet. The format of the XML fragment has been defined as below:
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