Maintainable 3D Models of Cities Gerhard NAVRATIL Rizwan BULBUL Andrew U. Frank Vienna University of Technology Institute of Geoinformation and Cartography

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Outline Problem Definition Definitions 3D City Models: Quality Classes How to Obtain the Data? Usage of 3D City Models Changes within Cities Model Updates Conclusions

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Problem Definition (1) 3D city models: active research field Topics include –Automatic building detection –Subsurface infrastructure modelling Major cities invest much to create such models (e.g., Berlin, Vienna)  Applications must justify the expenses

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Problem Definition (2) Applications rely on specific data quality Cities are constantly changing  deterioration of data quality Solutions –Revenue exceeds costs before the model becomes unusable –Model is constantly updated

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Definitions Models of Cities model of topographic relations between objects in cities, typically 3D Sustainability „…maintenance or improvement of the integrated natural systems that collectively comprise life on our planet.“ (Egger 2006) Includes ecological, economical, and social sustainability (Agenda 21, United Nations 1992) Maintainability „uphold as valid, just, or correct” (Nichols 2001)

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Quality Classes Quality classes from CityGML (Kolbe, Gröger et al. 2005) Level of detail 0 (LoD0): digital terrain model (DTM) + aerial image Level of detail 1 (LoD1): Block models of buildings Level of detail 2 (LoD2): Roof structures, textures Level of detail 3 (LoD3): Detailed roof and wall structures including balconies and vegetation Level of detail 4 (LoD4): Interior structures like rooms, doors, stairs, and furniture

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP How to Obtain the Data Aerial photography: Terrain model, block models of buildings, roof structures, wall textures (limited) Airborne laser scanning: Terrain model, block models, roof structures, vegetation Terrestrial survey: Terrain model to building interiors (high costs) Mix: Car-mounted fisheye cameras Architectural maps: Building interiors, underground structure (not for old structures)

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Usage of 3D City Models (1) Used in various domains: –urban planning and management –noise and air pollution –disaster management –Tourism –facility management –environmental management simulations –homeland security –real estate management –vehicle and pedestrian navigation –training simulators –etc.

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Usage of 3D City Models (2) Tool to visualize the existing city state (Döllner, Kolbe et al. 2006) Urban planning is a complex task involving the interplay between multiple aspects of a city  nD urban model (Hamilton, Wang et al. 2005) Tool for rescue operations during disasters (Kolbe, Gröger et al. 2005) Tool to model air pollution (Wang, van den Bosch et al. 2008)

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Usage of 3D City Models (3) Application AreaModel LOD Urban PlanningLOD0-LOD3 Noise PollutionLOD1-LOD3 Disaster ManagementLOD3, LOD4 Traffic ManagementLOD1 Air pollutionLOD0-LOD3

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Changes Within Cities Types of changes –Constant changes (replacement of building) –Temporal changes (snow, flooding, trenches) Types of constant changes –Creation, change, or destruction of a single object –Changing objects in a specific area

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Model Updates: LoD0 DTM: Changes by –Natural disasters: Typically dramatic changes, do not go unnoticed –Massive earth movement on construction sites: Reconstruction of affected area necessary, construction should be known

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Model Updates: LoD1 For building blocks important changes are –creation of new buildings, –destruction of buildings, and –massive change of a building shape Easy to detect if announcement necessary Automatic detection possible from aerial photos or ALS

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Model Updates: LoD2 Changes in roof structure: Like building blocks Wall textures –How to capture deterioration? –How to capture freshly painted buildings?

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Model Updates: LoD3 Changes in detailed roof structure –Like general roof structure, but lower flying height necessary  more data, higher costs –Small deviations: Change or noise?  On- site inspection? Changes in detailed wall structure –What if change not visible from above? Changes in vegetation –ALS, modelling may be difficult (Schönbrunn)

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Model Updates: LoD4 Only terrestrial survey possible What is a change? –Tearing down walls? –Replacement of furniture? –Winter vs. summer clothes in a shop?

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Conclusions (1) Maintenance more difficult for LoD4 than LoD0 Challenges are –receiving information about the change and –assessing the significance of a change  Main problem is data collection, not data modelling

Gerhard Navratil, Rizwan Bulbul, Andrew U. Frank CORP Conclusions (2) Strategies to deal with the problem –Keep the 3D city models simple –Allow different levels of detail for different parts of the city –Install processes that force citizens to provide data for significant changes Further investigation necessary on crowd sourcing or volunteered geographic information (Goodchild 2008)