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Shell model representation as a substitute of LOD3 for 3D modeling in CityGML
Department of Cartography, Technical University of Munich.
KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
Nanjing Normal University.
Department of Cartography, Technical University of Munich.
2011 (English)In: Geo-spatial Information Science, Vol. 14, no 2, 78-84 p.Article in journal (Refereed) Published
Abstract [en]

The OGC standard for 3D city modeling is widely used in an increasing number of applications. It defines five consecutive Levels of Detail (LoD0 to LoD4 with increasing accuracy and structural complexity), in which LoD3 includes all exterior appearances and geometrical details and subsequently requires much storage space. A new LoD is introduced as shell model with the exterior shell of the LoD3 model and the opening objects like windows, doors as well as smaller façade objects are projected onto walls. In this paper, a user survey is presented. The results of this survey show that the shell model can give users almost the same visual impression as the LoD3 model. Furthermroe, algorithms are developed to extract the shell model from LoD3 model. Experiments show that this shell model can reduce up to 90% storage of the original LoD3 model. Therefore, on one hand it can be used as a substitute for a LoD3 model for the visualization on small displays. On the other hand, it can be treated as a sub-level of detail (SLoD3) in CityGML, since it retains almost the same amount of information but requires much less storage space.

Place, publisher, year, edition, pages
2011. Vol. 14, no 2, 78-84 p.
Keyword [en]
shell model, 3D building, CityGML, generalization, user survey
National Category
Other Environmental Engineering
URN: urn:nbn:se:kth:diva-48163DOI: 10.1007/s11806-011-0445-8ScopusID: 2-s2.0-79956017582OAI: diva2:456887
Joint ISPRS Workshop on 3D City Modelling and Applications and the 6th 3D GeoInfo, 3DCMA 2011; Wuhan; China; 26 June 2011 through 28 June 2011

QC 20111116

Available from: 2011-11-16 Created: 2011-11-16 Last updated: 2014-09-15Bibliographically approved
In thesis
1. Visualisation and Generalisation of 3D City Models
Open this publication in new window or tab >>Visualisation and Generalisation of 3D City Models
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

3D city models have been widely used in various applications such as urban planning, traffic control, disaster management etc. Efficient visualisation of 3D city models in different levels of detail (LODs) is one of the pivotal technologies to support these applications. In this thesis, a framework is proposed to visualise the 3D city models online. Then, generalisation methods are studied and tailored to create 3D city scenes in different scales dynamically. Multiple representation structures are designed to preserve the generalisation results on different level. Finally, the quality of the generalised 3D city models is evaluated by measuring the visual similarity with the original models.


In the proposed online visualisation framework, City Geography Makeup Language (CityGML) is used to represent city models, then 3D scenes in Extensible 3D (X3D) are generated from the CityGML data and dynamically updated to the user side for visualisation in the Web-based Graphics Library (WebGL) supported browsers with X3D Document Object Model (X3DOM) technique. The proposed framework can be implemented at the mainstream browsers without specific plugins, but it can only support online 3D city model visualisation in small area. For visualisation of large data volumes, generalisation methods and multiple representation structures are required.


To reduce the 3D data volume, various generalisation methods are investigated to increase the visualisation efficiency. On the city block level, the aggregation and typification methods are improved to simplify the 3D city models. On the street level, buildings are selected according to their visual importance and the results are stored in the indexes for dynamic visualisation. On the building level, a new LOD, shell model, is introduced. It is the exterior shell of LOD3 model, in which the objects such as windows, doors and smaller facilities are projected onto walls.  On the facade level, especially for textured 3D buildings, image processing and analysis methods are employed to compress the texture.


After the generalisation processes on different levels, multiple representation data structures are required to store the generalised models for dynamic visualisation. On the city block level the CityTree, a novel structure to represent group of buildings, is tested for building aggregation. According to the results, the generalised 3D city model creation time is reduced by more than 50% by using the CityTree. Meanwhile, a Minimum Spanning Tree (MST) is employed to detect the linear building group structures in the city models and they are typified with different strategies. On the building level and the street level, the visible building index is created along the road to support building selection. On facade level the TextureTree, a structure to represent building facade texture, is created based on the texture segmentation.


Different generalisation strategies lead to different outcomes. It is critical to evaluate the quality of the generalised models. Visually salient features of the textured building models such as size, colour, height, etc. are employed to calculate the visual difference between the original and the generalised models. Visual similarity is the criterion in the street view level building selection. In this thesis, the visual similarity is evaluated locally and globally. On the local level, the projection area and the colour difference between the original and the generalised models are considered. On the global level, the visual features of the 3D city models are represented by Attributed Relation Graphs (ARG) and their similarity distances are calculated with the Nested Earth Mover’s Distance (NEMD) algorithm.


The overall contribution of this thesis is that 3D city models are generalised in different scales (block, street, building and facade) and the results are stored in multiple representation structures for efficient dynamic visualisation, especially for online visualisation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xii, 104 p.
Trita-SOM , ISSN 1653-6126 ; 2011>19
3D city models, visualisation, generalisation, multiple representation structure, similarity evaluation, aggregation, typification, shell model, street index, texture compression, texture segmentation
National Category
Other Environmental Engineering
Research subject
urn:nbn:se:kth:diva-48174 (URN)978-91-7501-189-9 (ISBN)
Public defence
2011-12-02, D2, Lindstedtsvägen 5, Entreplan, KTH, Stockholm, 10:00 (English)
QC 20111116Available from: 2011-11-16 Created: 2011-11-16 Last updated: 2011-11-16Bibliographically approved

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