Chapter 5 Visualization and Exploration of Large Semantic 3D City Models
5.3 Example Applications
In this subsection three typical use case examples are introduced to show the usability and feasibility of the developed 3D web client in practical projects. Each of these examples has been intentionally chosen to demonstrate the individual key features of the 3D web client that have been successfully realized based on the research work and technical implementation. These results of these use cases were obtained in the course of different research projects which were carried out by the research team at the Chair of Geoinformatics at Technical University of Munich. As a software developer, the author was involved in all these projects
Technische Universität München Lehrstuhl für Geoinformatik
Collaborative Work using the 3D Web Client
24.06.2017 WebGL-basierte 3D-Visualisierung von Stadtmodellen durch die Erweiterung von
Cesium 44 Administrator Public User Data Manager link link Configuration Thematic Data 1 Thematic Data 2 Cloud Service
and mainly worked on enhancing the 3D web client according to the requirements of the project partners.
5.3.1 3D City Model of New York City
The project “3D City Model of New York City” is a student project which has been carried out in the context of three master theses of Barbara Burger, Berit Cantzler, and Christof Beil within the master's program Geodesy and Geoinformation at TUM (cf. Kolbe et al. 2015, Beil & Kolbe 2017). The key objective of these student projects is to create a homogenized and integrated semantic 3D city model of New York City (NYC) from the existing public 2D and 2.5D datasets provided in the NYC Open Data Portal. To reach this purpose, different spatial and semantic transformations and manipulations together with some photogrammetric analyses were investigated and performed using the ETL tool Feature Manipulation Engine (FME) of Safe Software. The resulting 3D city model is managed as a single CityGML file which comprises a variety of 3D feature types including all NYC buildings, land parcels, roads, parks, the digital terrain model, and water bodies and can be downloaded as Open Data from the project home page of the Chair of Geoinformatics3. In addition, the CityGML dataset has been imported into a 3DCityDB instance for the efficient data maintenance and also been converted to tiled KML/glTF models for the 3D visualization on the Virtual Globe like Google Earth and Cesium. To explore the resulting 3D city model conveniently, all the generated 3D visualization models have been deployed using the 3D web client and a screenshot of the online demo is shown in Figure 98.
Figure 98: Example demo of visualizing 3D city model of New York City on the 3D web client
This 3D web client Demo contains all street space objects as well as all building objects of New York City in LoD2. More than one million building objects and more than 500'000 street
space objects were generated as tiled 3D visualization models separated into different layers according to the feature types. Moreover, each city object is enriched with a range of attribute information which have been uploaded and stored in the Cloud-based online spreadsheet ‘Google Fusion Table’ allowing for rich model exploration by clicking on the city object individually.
5.3.2 3D City Model of Berlin
Nowadays, a semantic 3D city model of the German capital Berlin is freely available to the public as open data in CityGML format. This 3D city model was created with the full coverage of the entire city area (890 km²) and comprises around 550,000 LoD2 building objects which are fully textured with the images photographed from the air (cf. Döllner et al. 2006). To date, this 3D city model is one of the largest textured CityGML models worldwide and can be obtained via a web-based service portal4 through which users can select and download individual building models in a variety of 3D data formats in addition to CityGML, e.g. OBJ, KML, COLLADA, and 3D-Shapefile. Therefore, the 3D city model provides a good foundation for the research and development of Smart Cities. For example, in the context of the research project “Energy Atlas Berlin”, this 3D city model has been utilized as an important information basis for developing the tools for holistic calculation of the energy consumptions, demands and saving potentials at an urban scale. The results of the calculation and simulations can be enriched to the 3D city models and shall be able to be explored on a 3D map. This has been realized using the developed 3D web client and a screenshot of a dedicated online demo is shown in Figure 99.
Figure 99: Example of visualizing 3D city model of Berlin on the 3D web client
In this example, each building object has been generated with three different display forms starting from the coarse “Extruded” geometry, via the untextured geometry up to the most
detailed textured geometry. Depending on the distance between the camera and the individual building object, one of the three geometry representations can be automatically chosen by the 3D web client for the display and can also be dynamically switched during the runtime according to the Level of Detail mechanism: The buildings being far away from the camera are simply rendered as extruded or untextured geometries, while the textured buildings with higher details will be rendered when viewing the building objects from a short distance. In this way, the efficient 3D visualization of the 3D city models with higher level of details (LOD ≥ 2) is possible.
5.3.3 3D City Model of Vorarlberg
In the context of the VoDLM3D (Semantisches 3D-Landschaftsmodell Vorarlberg) project, the Vorarlberg State Government plans to establish and provide a semantic 3D landscape model which shall contain comprehensive 3D spatial and thematic information on roads, water bodies, vegetation coverage, as well as topographic objects like buildings, bridges, tunnels, ski slopes, high-voltage lines and towers (cf. Marx et al. 2017). All these data shall be able to be administrated by the Vorarlberg government and can also be publicly accessible to the citizens from Vorarlberg based on a 3D web solution. For this purpose, the existing 2D/3D geospatial data of Vorarlberg have been first transformed to a CityGML data model using the software tool FME and then converted to the respective 3D visualization models with different data layers according to the topographic feature types. A subset of the project results is represented as a 3D web client demo which is accessible via the Github5. This demo (cf. Figure 100) shows around 9800 attributed LoD2 buildings along with an imagery base map according the OGC Web Map Service (WMS) as well as a high-resolution (0.5 meter) digital terrain model resulted from converting a GeoTIFF-formatted DTM to the Cesium- compliant heightmap format.
Figure 100: Example of visualizing 3D landscape model of Vorarlberg on the 3D web client 5https://github.com/3dcitydb/3dcitydb-web-map#demos