Assessment of 3D Geoportals of Cities According to CityGML Standard Guidelines

Along with the development of three-dimensional computer graphics, methods of collecting and making 3D spatial data available became a significant issue covering the interoperability of data derived from multiple sources. Between 2006 and 2008, the Open Geospatial Consortium designed a CityGML model as a proposal for a uniform classification, graphic representation, construction, and storage of 3D objects. A considerable part of three-dimensional visualisations, now gaining popularity, make use of solutions based on the CityGML standard, with which they are compatible to various degrees. The survey involved a comprehensive analysis of sixteen generally accessible 3D geoportals of cities in Europe, Asia, and North America in terms of their broad-sense functionality as well as technical and thematic compatibility with the assumptions of CityGML standards. The level of realisation of various features related to the provided spatial data services was evaluated, taking into account elements that the present-day world literature deems to be particularly desirable. The analysis resulted in an elaborate ranking of websites according to 21 criteria. The most common objects and features of the analysed geoportals were also detailed. In addition, the authors presented several solutions to improve the quality of three-dimensional geoportals of cities by implementing external data from various sources.