Conforming building models derived in Esri's environment to the Swedish national specification for 3D data

University essay from Lunds universitet/Institutionen för naturgeografi och ekosystemvetenskap

Abstract: Three-dimensional (3D) city models are increasingly utilized among stakeholders of different sectors, particularly those dealing with building information. 3D city models are a three-dimensional digital representation of urban structures, most prominently buildings. They offer diverse applications and have gained wide acceptance as a support tool in planning practices. The push to achieve greater interoperability in the GIS sector has been a motivating factor for standardized practices for 3D city models. National frameworks for 3D data have been established in several countries to facilitate information sharing between different actors such as municipalities or other administrative bodies. A national specification (NS) pertaining to 3D data is in development in Sweden, along with a standard aimed explicitly at 3D building models, denoted as NS building. Municipalities will have to adjust their modeling practices to adhere to the standard in the future realization of their 3D city models. Proprietary software, such as Esri, has been common to establish 3D city models in the context of municipalities in Sweden. The interoperability of pre-existing 3D building models derived in an Esri environment with NS building has not yet been addressed. This thesis aimed to propose a workflow to transform Esri-derived building models and conform them to the NS building standard to assess the applicability of the Swedish standard for building models in Esri MultiPatch format. As a case study, a 3D city model from the municipality of Karlskrona was used to develop a method of transformation between the formats. The project results were that a script that streamlines the process of converting building models in Esri MultiPatch format to NS building could be established. For this, a spatial Extract, Transform, and Load (ETL) process was developed and realized using Safe Software's Feature Manipulation Engine (FME). The process centered around making the geometries and attributes of the test dataset compatible with NS building models of different levels of detail (LoDs) through the process of de-aggregation, restructuring, and defining surfaces according to their types (bottom, roof, or wall surfaces). Each LoD was represented as a single feature class, and the attribute table was stored in a stand-alone manner, sharing a common identifier with the building models. The output models and the attribute table could be stored in the initial Esri file geodatabase (File GDB). The script that this thesis presents manages to capture all purely Esri-derived models and model them according to the Swedish standard, with separated surfaces of the bottom, roof, and wall parts relevant to the different LoDs required of the Swedish standard. This excludes the creation of roof surfaces for one of the LoDs represented in the standard. Moreover, as the standard was still in development at the time of writing, the presented workflow may need to be subjected to changes in the future and edited if it were to be better inclusive of a multi-source dataset, as opposed to solely Esri derived. The externally sourced models present in the test data introduced more nuance, which was difficult to account for on all fronts.

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