The Singapore Government has embarked on a project to establish a three-dimensional city model and collaborative data platform for Singapore. The research herein contributes to this endeavour by developing a methodology and algorithms to automate the conversion of Building Information Models (BIM), in the Industry Foundation Classes (IFC) data format, into CityGML building models, capturing both geometric and semantic information as available in the BIM models, and including exterior as well as interior structures. We adopt a Triple Graph Grammar (TGG) to formally relate IFC and CityGML, both semantically and geometrically, and to transform a building information model, expressed as an IFC object graph, into a city model expressed as a CityGML object graph. The work pipeline includes extending the CityGML data model with an Application Domain Extension (ADE), which allows capturing information from IFC that is relevant in the geospatial context but at the same time not supported by CityGML in its standard form. In this paper, we elaborate on the triple graph grammar approach and the motivation and roadmap for the development of the ADE. While a fully complete and lossless conversion may never be achieved, this paper suggests that both a TGG and an ADE are natural choices for supporting the conversion between IFC and CityGML.

Industry Foundation Classes (IFC), the buildingSMART open standard for BIM, is underused with respect to its promising potential, since, according to the experience of practitioners and researchers working with BIM, issues in the standard’s implementation and use prevent its effective use. Nevertheless, a systematic investigation of these issues has never been carried out, and there is thus insufficient evidence for tackling the problems. The GeoBIM benchmark project is aimed at finding such evidence by involving external volunteers, reporting on various aspects of the behavior of tools (geometry, semantics, georeferencing, functionalities), analyzed and described in this article. Interestingly, different IFC software programs with the same standardized data sets yield inconsistent results, with few detectable common patterns, and significant issues are found in their support of the standard, probably due to the very high complexity of the standard data model. A companion article (Part II) describes the results of the benchmark related to CityGML, the counterpart of IFC within geoinformation.

Much work has been done on quality of geoinformation and interoperability between BIM and GIS. However, the intersection of the two – quality control of the conversion between BIM and GIS – remains uncharted. This discussion paper, based on empirical results, is one of the first steps towards mapping out a framework on errors and quality control in the context of BIM–GIS interoperability. In our work we focus on the conversion from IFC to CityGML, identifying several systematic errors potentially common and/or exclusive to the context of BIM–GIS conversion. Besides exposing several faults pertaining to IFC-sourced 3D city models, we discuss their taxonomy and their potential impact when engaged in applications. This paper is also relevant with respect to the growing popularity of conversion between IFC and CityGML, potentially aiding others to avoid many of the errors that can occur in the process and establishing directions to set up a benchmark to assess the performance of the interoperability workflows.

This paper (1) discusses the modelling of floor plans in CityGML; (2) proposes a delineation of multiple variants of indoor LoD0 in line with the current proposal for CityGML 3.0; (3) demonstrates a method to generate CityGML datasets with included floor plans; and (4) explores their usability. The use of an Application Domain Extension (ADE) is being proposed in order to preserve potentially useful information found within detailed building information models (BIM), specifically Industry Foundation Class (IFC), that cannot be stored in CityGML natively. Our work follows the current developments of CityGML 3.0, and based on the discussions in the CityGML Standards Working Group (SWG) it showcases one of the first datasets consistent with the ongoing development of CityGML 3.0 and one that follows the proposals for a new LOD concept and new interior features.

In model transformation, the population of attributes on the target side constitutes the last step of the conversion process that carries over that part of the input which is often perceived as the most valuable actual information. We are employing a graph-based model transformation approach to convert building information models into geospatial city models. In this paper, we are reporting on different types of transformation rules to populate the attributes on CityGML side using information extracted from the IFC data. We document the various ways how attribute values can be stored in IFC and CityGML respectively and identify patterns that bridge these endpoints in the conversion process. These patterns lead to a set of prototypical graph transformation rules which have been applied to a range of building projects. The novel graph-based approach to IFC-to-CityGML conversion implicates an intuitive visual representation of these rules. This work can also serve as a starting point to convert IFC data to other formats or to populate CityGML from other data sources.

Conversion of Industry Foundation Classes (IFC) building models into CityGML city models is one of the operational scenarios for BIM–GIS integration, with a variety of applications producing and consuming data on either side. Given the in‐depth cross‐domain knowledge required to specify such conversions, the heterogeneity of the IFC input data and the use cases for the resulting CityGML, flexible and configurable solutions are needed that make conversion details accessible to domain specialists. Graph transformation as a conversion method fulfils these requirements. We propose to extend the modularity given by single transformation rules at a more coarse‐grained level and identify four layers with modules of associated rules. We describe a self‐contained set of rules across these modules and demonstrate its application to a range of building models.