Visualisering av stadsmodeller på webben
Sammanfattning: As the technological developments and the access to 3D geographical data is increasing the usage of city models in planning is becoming more important. City models have traditionally mainly been used for visualization but are now an important tool for analysis. The increased application of city models set higher requirements on standardized formats to effectively exchange data. City models are commonly stored in the information model CityGML. However, CityGML has been described as problematic to work with, especially on the web. The criticism is mainly due to the XML-coding being hard to work with, its verbose and hierarchic structure and the large file size. The purpose of this report is to examine if CityJSON is an appropriate alternative to the XML-implementation of CityGML 2.0 for visualization of geometries and attribute data on the web. In this study, two strategies for visualization are compared. The evaluation is thus being done indirectly by comparing the two strategies. In the first strategy an existing tool for visualizing CityJSON is being further developed. City models are in this strategy being visualized directly in the web browser in CityJSON format. In the second strategy an application for CityGML is developed using the platform Cesium. In this strategy CityGML is converted to 3D-tiles. The two strategies are then evaluated from a set of requirements. The study shows that the CityJSON-format has multiple advantages compared to using CityGML and the Cesium platform on the web. CityJSON data used in this study is up to ten times more compact compared to the corresponding file in CityGML-format. This results in faster transfer and management of the data on the web. The study also shows that Cesium has problem with handling attribute data and is more suitable for pure visualizations. This is due to information being lost in the conversion to 3D-tiles and that the data is saved remotely and being streamed to the client. In conclusion, this study shows that CityJSON is a promising format and have potential to ease the development of applications for city models on the web.
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