Visualizing and Editing GIS data with SVG for Internet and Mobile Users

Miss. Ida K.L CHEUNG  a , Mr. Geoffrey Y.K. SHEA b

a Department of Land Surveying & Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom,   Kowloon, Hong Kong, email: ida.cheung@polyu.edu.hk

 b Department of Land Surveying & Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, email: geoffrey.shea@polyu.edu.hk

Keywords: SVG, GML, GIS, XML, Web mapping

The widespread availability of the World Wide Web has led to a rapid increase in the amount of data accessing, sharing and disseminating. This gives the opportunities for delivering maps over the Internet as well as small mobile devices. In a GIS industry where there are many vendors or companies, they have produced their own web map products which have their own version, data model and proprietary data formats. They are not able to talk with each other. Such problem has long been an issue and therefore Geography markup Language (GML) was designed to help solve. GML is an XML grammar written in XML Schema for the modelling, transport, and storage of geographic information including both spatial and non-spatial properties of geographic features. It is developed by Open GIS Consortium in order to promote spatial data interoperability and open standard.

As GML is not for data display, SVG is an ideal vector graphic for displaying geographic data. GML sets at the backend to store and transport data and on the other side SVG sets on front end to render and display geographic data.  They not only can visualize geographic data on the web, but also give the possibility to edit geographic data online. This research therefore is to develop efficient algorithms of editing geographic data online and in mobile devices. It explores whether using GML and SVG is a good method to intergrate web-based mapping information in terms of data modelling, spatial data presentation represertation mechanism and spatial data editing capability. Especially in Internet and wireless environment, whether using GML and SVG gives a significant improvement of bandwidth, speed, access and reliability. Since SVG is text-based and vector format, it is expected that downloads can be considerably shortened and even more important for bandwidth is the scalability inherent to vector lines. In this way, the performance can be substantially improved.

In order to test the capability of displaying and editing geographic data, a prototype is built. It aims to investigate the capability of GML and SVG and develop a corresponding data modeling and system in order to overcome or improve the existing limitation on online graphic presentation and data editing functions. It will focus on online map editing function which is still not well developed function over existing web mapping system and examine specific problems and approaches in using SVG as a user interface for editing geographic data online.  The prototype will be implemented in client and server model. The prototype will involve:

a.       GML data and application schema generation: As Hong Kong basemap data originally are in ArcInfo coverage format, data are needed to generate into GML first. Also, a conceptual model of GML and SVG data will be built. It is specially applied for describing and modeling topographic features in Hong Kong. Specific application schema will be generated to validate GML data.

b.      XSL stylesheet generation and graphic presentation: Stylesheets are used to convert and format GML into SVG and different style and symbols can be applied. The stylesheet also defines the graphic presentation of the map. A set of recommended styles and symbols for the portrayal of basemap data is specified.   

c.       Design algorithms for editing function: This is the major part of the prototype.  As SVG offers more than vector display, SVG document can be added, moved, modified, copied and deleted using client triggered graphical user interface events. By developing some common scripting language like Javascript, it can track the mouse and transform the user coordinate on client machine to the user-defined coordinate system. This makes onscreen digitizing online possible and then allows adding and updating data. The functions will include move, add and delete feature and vertex and modify textual information. The client interface will be implemented for both Internet and mobile users. After finished modification, the modified part of SVG document will be transferred and converted back to GML data in the server.