Differences in the scope and intent of the contrasting IFC and CityGML data formats entail that converting the former to the latter results in loss of information. However, for some use cases it is beneficial to keep also particular information from IFC that is not native to CityGML, and achieving that requires mechanisms such as the CityGML Application Domain Extension (ADE). We develop an ADE to support retaining relevant information from IFC. Besides being driven by the particular source of the input data (IFC), this multipurpose ADE is shaped after a discovery process that involved examining potentially applicable use cases in Singapore, doubling as an extension that is adapted to a set of use cases and the local geographic context. We implement the conceptual work by generating an enriched dataset (with an automatic conversion from IFC to CityGML), visualising it, and discuss its added value in a use case.
There is an increasing activity in developing workflows and implementations to convert BIM data into CityGML. However, there are still not many platforms that are suitable to view and interact with the detailed information stored as a result of such conversions, especially if an Application Domain Extension (ADE) is involved to support additional information. We investigated the ease of use and features supported by visualisation software and tools with CityGML and ADE support, and propose an approach to develop a tool that combines useful features using a set of generic rules that can extract CityGML ADE attributes. The work, while generic, is geared towards detailed architectural datasets sourced from BIM. We implemented the approach in a web-based viewer supporting the visualisation of CityGML datasets enriched with ADE 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.
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.
The Application Domain Extension (ADE) is a built-in mechanism of CityGML to augment its data model with additional concepts required by particular use cases. The goal of this paper is to provide an overview of the ADE mechanism and a literature review of developments since its introduction a decade ago. The discovery of publications found that currently there are 44 ADEs supporting a wide range of applications, but also application-agnostic purposes such as harmonisation with national geographic information standards. We hope this paper to double as a reference material for the developers of new ADEs.
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.
A triple graph grammar approach is adopted as a formal framework for semantic and geometric conversion of IFC models into CityGML Level of Detail 3/4 building models. The triple graph grammar approach supports a semantic mapping from IFC to CityGML, the generation of conversion routines from this mapping, and an incremental approach to achieving a "complete and near-lossless" mapping. The objective of this approach is the development of a methodology and algorithms to automate the conversion of Building Information Models into CityGML building models, capturing both geometric and semantic information as available in the BIM models, in order to create semantically enriched 3D city models that include both exterior and interior structures.