Automatic Unfolding of CityGML Buildings to Paper Models

Steffen Goebbels,Regina Pohle-Fröhlich

doi:10.3390/geographies1030018

Abstract

3D city models are mainly viewed on computer screens, but many municipalities also use 3D printing to make urban planning tangible. Since 3D color printing is still comparatively expensive and the colors often fade over time, many of these models are monochrome. Here, color textured paper models offer an inexpensive and under-appreciated alternative. In this paper, a greedy algorithm adapted to CityGML building models is presented, which creates print templates for such paper models. These 2D layouts consist of cut edges and fold edges that bound polygons of a building. The polygons can be textured or left blank depending on the existence of CityGML textures. Glue tabs are attached to cut edges. In addition to the haptic 3D visualization, the quality of the 3D models can sometimes be better assessed on the basis of the print templates than from a perspective projection. The unfolding procedure was applied to parts of the freely available CityGML model of Berlin as well as to parts of models of the cities of Dortmund and Krefeld.

Highlights

Virtual 3D city models are used for simulation purposes as well as for vivid visualization of urban planning, e.g., see [1]
In the CityGML level of detail 1 (LoD 1), the building footprint is extruded to obtain a 3D object with a flat roof
Paper models can potentially be used for urban planning and are a comparatively easy-to-create and cost-effective alternative to virtual 3D visualization as well as manuallycreated or 3D-printed architectural models

Summary

Introduction

Virtual 3D city models are used for simulation purposes (e.g., solar potential analyzes, flood maps, heat requirement mapping) as well as for vivid visualization of urban planning, e.g., see [1]. They are a data source for Building Information Modeling (BIM), see [2]. Most CityGML models are currently specified in a level of detail that provides somewhat simplified roof facets and walls but lack detailed facade information. In the CityGML level of detail 1 (LoD 1), the building footprint is extruded to obtain a 3D object with a flat roof. The CityGML level of detail 2 (LoD 2) allows for arbitrary planar roof facets. If color printing is used, this is even more true for those models that have been textured with oblique aerial images, see Figure 1

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Results

Conclusion