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ABSTRACT:CityGML is considered as an optimal standard for representing 3D city models. However, international experience has shown that visualization of the latter is quite difficult to be implemented on the web, due to the large size of data and the complexity of CityGML. As a result, in the context of this paper, a 3D WebGIS application is developed in order to successfully retrieve and visualize CityGML data in accordance with their respective geometric and semantic characteristics. Furthermore, the available web technologies and the architecture of WebGIS systems are investigated, as provided by international experience, in order to be utilized in the most appropriate way for the purposes of this paper. Specifically, a PostgreSQL/ PostGIS Database is used, in compliance with the 3DCityDB schema. At Server tier, Apache HTTP Server and GeoServer are utilized, while a Server Side programming language PHP is used. At Client tier, which implemented the interface of the application, the following technologies were used: JQuery, AJAX, JavaScript, HTML5, WebGL and Ol3-Cesium. Finally, it is worth mentioning that the application's primary objectives are a user-friendly interface and a fully open source development.

ABSTRACT:Smart cities are applied to an increasing number of application fields. This evolution though urges data collection and integration, hence major issues arise that need to be tackled. One of the most important challenges is the heterogeneity of collected data, especially if those data derive from different standards and vary in terms of geometry, topology and semantics. Another key challenge is the efficient analysis and visualization of spatial data, which due to the complexity of the physical reality in modern world, 2D GIS struggles to cope with. So, in order to facilitate data analysis and enhance the role of smart cities, the 3 rd dimension needs to be implemented. Standards such as CityGML and IFC fulfill that necessity but they present major differences in their schemas that render their integration a challenging task. This paper focuses on addressing those differences, examining the up to date research work and investigates an alternative methodology in order to bridge the gap between those Standards. Within this framework, a generic IFC model is generated and converted to a CityGML Model, which is validated and evaluated on its geometrical correctness and semantical coherence. General results as well as future research considerations are presented.

<p><strong>Abstract.</strong> CityGML is considered an optimal standard for the representation of 3D city models. However, due to its complex structure, easy-to–use data retrieval is important, in terms of interoperability. This implies choosing the implementation of Web Service Technologies and in particular the WFS, as the most suitable OGC standard for retrieving the real geometry data. Nevertheless, this standard serves data mainly based on their geometry, while CityGML also covers topology and more importantly semantic aspects of 3D city models. Therefore, this paper examines and presents the new CityGML RESTful Web service, instead of the OGC WFS. This Web Service is conceptually designed to achieve CityGML data retrieval based on their semantics characteristics. In this context, several principles and guidelines of the new CityGML RESTful Web service are described and the “CityModels” resource is presented. Additionally, the conceptual design of the bldg resource and its child resources based on the level of details is also presented.</p>

The rapid development of the technology of the web systems and GIS, in conjunction with the world economic crisis, formed the content for the promotion and development of free systems and open-source technologies. At the same time, the tendency toward the standardization of data, metadata and services, with the aim of creating common "Language" for the reading and the dissemination of information available, is a basic research area in the global scientific community in this field. The development of WebGIS systems, taking advantage of the free technology, also contributes to finding more economical solutions, where the use of such systems is more directly accessible. The aim of this research work is, through the analysis of technologies for the Internet, and also the architecture of the WebGIS systems, to investigate the possibilities and to develop the appropriate free technologies, so as to design and implement a spatial content management system for the web. Search with the use of the latter, is the best response to the needs and visualization application maps, with scope in rural areas. In addition, reference is made to the existing content management systems, which provide both processing spatial data, and easily create a WebGIS application.

Abstract. Smart Cities are complex distributed systems which may involve services, applications, sensors and IoT devices. In order to be able to link and use such heterogeneous data, spatial data infrastructures for Smart Cities can play an important role in establishing interoperability between systems and platforms. Semantic 3D city models describe spatial, graphical and thematic aspects of the city objects according to the CityGML international standard, issued by the Open Geospatial Consortium (OGC). The requirement to support energy time-dynamic properties within CityGML objects arises from the fact that cities yield great potential in terms of energy consumption reduction and efficiency increase. In order to support such time-varying energy properties concerning city objects, recent extensions of the CityGML in the form of Application Domain Extensions (ADEs) are researched and developed, such as the Energy ADE and the Dynamizer ADE. Starting from a Building Information Model (BIM) and evaluating energy use of the building through the created Building Energy Model (BEM), the aim of this study is to integrate and visualize the time-based energy simulation results with the 3D building model within a 3D semantic city model. Using the latter ADE, the highly detailed static 3D Building (LOD 4) is extended to support those energy variations of individual feature properties and associations over time. Moreover, the web-based visualization approaches and data retrieval were further researched, and an interoperable web-based application was developed, in order to accomplish an integrated knowledge on how time-series data can be distributed in a virtual 3D environment.

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<p><strong>Abstract.</strong> Rapid urbanisation relates to increased space requirements above and below ground and the development of complex structures. This profound need attracted increasing interest for the collection, modelling, management, visualisation and dissemination of 3D objects through various application fields, such as: 3D Cadastre, 3D City Modelling and Building Information Modelling. Contemporary advances in GIS technology, Geo-Web services and computer graphics facilitate the development of such models accompanied by semantic, geometrical and topological information, while the use of international standards enables the communication and interoperability between the systems. The aim of this paper is to combine state-of-the art methodologies and technologies for the development of semantically enriched 3D models for the Campus of the National Technical University of Athens in Greece. The result is a web-based 3D Campus map that integrates these models as Web Services, providing access to management and navigation for the campus area and can also be used for maintenance purposes from the various NTUA Departments. To this end, the database schema has been designed compatible with CityGML, while attention was given to interoperability issues that arise from differently derived 3D models which had to be stored and visualised while retaining their characteristics.</p>