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From base maps to 3D city models

A Master’s thesis by Sito’s employee Oskari Liukkonen, The path of municipal geographical information from base maps to 3D city models, is a part of a 3D city model project (KM3D) carried out by the Association of Finnish Local and Regional Authorities and BuildingSmart. Liukkonen’s thesis provides municipalities with guidance on how to replace base maps with city models

The Association of Finnish Local and Regional Authorities’ geographical information team set up the KM3D project in partnership with BuildingSmart for the purpose of mapping the current state, development and standardization of 3D city modelling in Finland. The project has focused on studying CityGML, an open city model standard, and its potential for Finland’s national standard for 3D city modelling.

CityGML is an open international standard for the storage and exchange of data, approved by Open Geospatial Consortium (OGC). It defines five levels of detail (LOD) for the most relevant topographic objects in cities with respect to their geometrical, topological, semantical and appearance properties.

The focus of CityGML’s development has been on creating common definitions for the semantic characteristics, structures and classifications of 3D city model objects. The semantic properties of CityGML differentiate it from purely geometric 3D city models. In addition to visualization, semantics enable the use of CityGML city models in a range of applications, along with planning, analysis and simulation tasks, says Oskari Liukkonen.

“The objective of my Master’s thesis was to create municipal guidelines for replacing base maps with a CityGML-based 3D city model, and to point out factors that municipalities should consider during this transition. My purpose was to discover how data exchange, production, maintenance, administration and validation of a 3D city model should be implemented, and what should be taken into consideration with regard to existing geographical information work processes, in order to make 3D city models feasible and sustainable in the long term,” he continues.

Liukkonen’s thesis resulted in a four-step guideline:

  1. 3D city model knowhow;
  2. Identification of needs and use cases;
  3. 3D city model structure and data exchange;
  4. 3D city model processes: production, maintenance, validation and administration.

In order to make 3D city modeling feasible and sustainable in the long term, municipalities should consider at least the four following conclusions:

  • Municipalities should acquire the necessary know-how in 3D city modelling;
  • 3D city modelling should be based on needs-oriented use cases;
  • Production and maintenance of a 3D city model should be based on standardized data gathering and modelling processes that will enable, at least, semiautomatic production of a 3D model based on the use cases;
  • 3D city model maintenance, administration and data transfer should be thought out before the production stage, and the completed model should be compatible with the existing work and service processes.

“I found this research project interesting because the issue is so topical. 3D city models with their uses and development are a very important step towards digitalized smart cities. The smart city approach requires a city data model, which guides the operation of a smart city by storing and using the information constantly generated by the city.  The most challenging aspect of the thesis was the definition of the subject area and the objective, as 3D city models could be approached from several angles,” Liukkonen concludes.