Abstract
Three-dimensional graphical applications can provide an added value to Location Based Mobile Services (LBMS). This is particularly true for the applications related to urban environments, which can interactively present three-dimensional models to the user, visualized in accordance to his location. Modelling an urban environment is mainly a manual procedure and so it can become a difficult, tedious and time consuming task, due to the many different geometries, textures, details, etc, involved in the urban structures. This paper presents the XL3D modelling system that provides, in an automatic fashion, three-dimensional models of urban areas to be used in a LBMS Project. The XL3D modelling system is based on interoperable access to digital data, in diverse formats, accessing XML documents or invoking Web services in a distributed architecture. The system is driven by L-systems based modelling processes that automatically generate three-dimensional models of urban environments, specified in a declarative mode using documents based on an XML Schema, also called XL3D. Copyright © 2005 by the Association for Computing Machinery, Inc.

Abstract

Abstract
The municipal planning and management tasks are generally performed based on text documents or through digital maps provided by geographic information systems (GIS). However, most municipal GIS follow different data models, leading to interoperability problems when there is a need to combine data from different sources. Furthermore, most of the time these tasks are performed in a collaborative way between the municipal technicians, emerging some difficulties in decision making due to the three-dimensional nature of urban space. Thus, this paper describes a methodology which can integrate multiple sources of real data from diverse municipal GIS, in a unified data model based on the CityGML specification. This model is mapped onto an urban ontology oriented for procedural modeling, which, in turn, produces the threedimensional models of the urban environments. The system developed operates in a client-server approach, where the server is responsible for mapping the urban information to the unified data model and the client represents the procedural modeling technology that generates the urban environment in three-dimensional format, allowing users to interact and amplify the existing urban information.

Abstract
This paper presents Geospatial L-systems, a new extension of L-systems that incorporates geospatial awareness, and shows an application of this new tool in the expeditious modelling of urban environments, integrated with a modelling system with interoperable access to data sources. L-systems have been used in Computer Graphics for the modelling of plants, and in a few experiments to model urban environments. However, the lack of geospatial awareness is a limitation and in spite of some developments like open l-systems introduced the ability to communicate with the environment, there was a need for more flexibility. A new modelling system, named XL3D, generates virtual urban environments automatically from a XL3D document with a modelling specification. This modelling system accesses data sources in a interoperable way and the modelling processes are based on L-systems. The integration of geospatial L-systems with the XL3D modelling system has increased its potential for automation and improved the potential to generate virtual urban environments with a higher level of detail and visual fidelity, with a lower level of complexity of the modelling processes. These facts are shown in a case study where a virtual urban environment taken from an area in the Porto downtown is generated by this solution. © The Eurographics Association 2006.

Abstract
Nowadays, there is a wide range of commercial LBMS (Location-Based Mobile Services) available in the market, mainly in the form of GPS-based navigation solutions, and a trend towards the display of 3D maps can be clearly observed. Given the complete disparity of ideas and a visible commercial orientation in the industry, the study of the visualisation aspects that influence user performance and experience in the exploration of urban environments using 3D maps becomes an important issue. In this work, a generic conceptual framework is proposed whose main purpose is to objectively evaluate the impact and contribution of the major visualisation elements involved (henceforth mentioned as feature vectors). With this framework in mind, an online questionnaire was developed and administered to 149 test subjects in order to measure the real impact of feature vectors. The results clearly demonstrated that certain features have clear impact on user performance, and should be taken in account in LBMS development. As an example, just by displaying buildings with a 3D appearance, subjects were able to match more accurately the real environment with the one presented on a mobile device. In general, users were able to perform the tasks entrusted to them faster, if they were provided more realistic imagery.

Abstract
Nowadays, there is a wide range of commercial LBMS (Location-Based Mobile Services) available in the market, and a trend towards the display of 3D maps can be clearly observed. Given the complete disparity of ideas and a visible commercial orientation in the industry, the study of the visualization aspects that influence user performance and experience in the exploration of urban environments, using 3D maps, becomes an important issue. Based on a proposed conceptual framework, an online questionnaire was developed and administered in order to measure the real impact of each element. Combining the experimental results with the current state-of-the-art, a new visualization paradigm is defined in a dual specification: "layers" providing relevant visual content to the map, and "functions" providing the necessary functionality.