Modeling SVG and GML data for the Cartographic Generalization and the Multiple Representation on the web.

 

E. Gbei, I. Cosma, B. Moulin, N. Jabeur

Laval University, Department of Computer Sciences and Software Engineering

{ Edouard.gbei, ioana-mihaela.cosma, Bernard.Moulin, Nafaa.Jabeur, } @ift.ulaval.ca

 

Keywords:

Web mapping, SVG, GML, XML, geodata modeling, multiple representation, cartographic generalization

 

 

Abstract:

One of the main bottlenecks when trying to use cartographic generalization for real time map production is the difficulty to handle large amounts of geo-spatial data required by the generalization process. In most cases the large volumes of raster, vector data and other types of data to be processed, displayed and to be transmitted are prohibitive because of limited network speed, bandwidth, incompatibility of data formats and lack of efficient data structures in wired and wireless environments.

 

The aim of this paper is to address several issues related to the manipulation of spatial data structure for real time cartographic generalization. We propose a conceptual model of GML/SVG data based on the exploitation of Scalable Vector Graphics (SVG) features as well as Geographic Markup Language (GML) data structures for mapping applications in wired and wireless environment along with the use of the cartographic generalization and multiple representations. The implementation issues of this GML/SVG model for cartographic applications address successfully different topics such as the map on demand, data storage and data transfer in the context of the web and wireless system. We use tourism application to illustrate the use of this model

 

1. Introduction

 

The Scalable Vector Graphics (SVG) is an emerging two-dimensional vector graphics standard. The Geographic Markup Language (GML) provides a vendor neutral as well as implementation neutral format suited for distribution of geodata over a network. Developed respectively by W3C organization and Open GIS Consortium (OGC), the SVG and GML are XML dialects that add flexibility to mobile cartography and provide a dynamic way of presenting spatial data to a mobile user based on his context and his profile. SVG and GML are suited for context sensitive mapping. They are fully compatible with XML and its children XSL, CSS, XLink, XPointer, SMIL, XHTML.

 

Moreover their native capabilities can be extended in order to implement certain cartographic generalization operators. For more complex cases, extensions using XSLT, Java or other object oriented languages can be used (Letho et al. 2001). The combined SVG and GML technology can be used adequately in order to perform generalization operations and multiple representations as an alternative to traditional geometric algorithms. In the GiModig project (a recent European project which addresses real-time generalization of spatial data suited to mobile devices with different display resolutions [Sarjokoski et al. 2002]), the authors emphasised the need for research on real-time generalization and small-display cartography as well as methods to transfer vector-formatted data to wireless devices using the standards GML and SVG. We believe that the efficient use of these technologies for mapping applications requires an efficient data structure that can support both multiple representation and cartographic generalization.

 

The paper contains three main sections. First, we present an overview of SVG/GML technologies and their capabilities for on-the fly map production. Then we discuss and propose a multiple representation data modelling approach using SVG/GML standard, the pre-computed pictographic database approach is exposed. The paper ends with a summary and an overview of further investigations.