Abstract

3D building models of the world exhibit multi-scale properties. Different level-of-details (LoDs) are important for different applications. Therefore, generation of multi-scale representation of 3D building models to fulfill the demands of these applications is a generalization problem. In order to generalize 3D buildings, different pieces of information need to be preserved or removed to restrict the amount of data represented on a certain LoD. In this work, a three-step strategy based on simplification, aggregation and reconstruction of generalized buildings represented in City Geography Markup Language (CityGML) is proposed. The minimum length of edges (threshold value) for removal of amount of data is restricted to generalization specifications of CityGML characterized by differing accuracies and minimal dimensions of objects for each LoD. The main part of this paper is simplification of ground plans. For this purpose, a new approach is proposed to restrict number of edges, curves, and corners of ground plan of 3D building model on a certain LoD. Algorithms for simplification with the aim to derive LoD1 from exterior shells of buildings at LoD3 are implemented and tested on a number of buildings of Putrajaya city. The experiments showed that length of edge as threshold value is directly proportional to the size of generalized models.

Highlights

  • City Geography Markup Language (CityGML) as Open Geospatial Consortium (OGC) standard is one of the modelling tool used to model and represent components of buildings such as outer shells, openings, outer building installations, interiors at different level-of-details (LoD1–LoD4) (Groger et al 2007)

  • A three-step strategy based on simplification, aggregation and reconstruction of generalized buildings represented in City Geography Markup Language (CityGML) is proposed

  • The result of all proposed simplification and aggregation procedures presented in this paper, to derive LoD1 of building models of Putrajaya city of Malaysia are visualized in LandXplorer CityGML Viewer V. 2009

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Summary

Introduction

City Geography Markup Language (CityGML) as Open Geospatial Consortium (OGC) standard is one of the modelling tool used to model and represent components of buildings such as outer shells, openings (windows, doors), outer building installations, interiors (chair, table, decorations, etc.) at different level-of-details (LoD1–LoD4) (Groger et al 2007). Ground plans of 3D building models consist of a combination of features like points, lines and curves Simplification methods such as point-reduction (Douglas and Peucker 1973), edge move (Buchin et al 2011) and removal/adjustment of shortest edge (Fan and Meng 2009, 2012; Mao et al 2011); Sester and Brenner (2004) and (Baig and Rahman 2013) can be applied to simplify ground plans. With the aim to complete generalization, simplified structures of ground plans of walls and roofs need to be adjusted For this purpose, height of the bounding box or length of highest wall at LoD1 is considered.

CityGML generalization specifications
Generalization framework and workflow
Objects as real features
Reconstruction of generalized models
Implementation and results
Concluding remarks
Full Text
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