The integration of 3D city models with Building Information Models (BIM), coined as GeoBIM, facilitates improved data support to several applications, e.g., 3D map updates, building permits issuing, detailed city analysis, infrastructure design, context-based building design, to name a few. To solve the integration, several issues need to be tackled and solved, i.e., harmonization of features, interoperability, format conversions, integration of procedures. The GeoBIM benchmark 2019, funded by ISPRS and EuroSDR, evaluated the state of implementation of tools addressing some of those issues. In particular, in the part of the benchmark described in this paper, the application of georeferencing to Industry Foundation Classes (IFC) models and making consistent conversions between 3D city models and BIM are investigated, considering the OGC CityGML and buildingSMART IFC as reference standards. In the benchmark, sample datasets in the two reference standards were provided. External volunteers were asked to describe and test georeferencing procedures for IFC models and conversion tools between CityGML and IFC. From the analysis of the delivered answers and processed datasets, it was possible to notice that while there are tools and procedures available to support georeferencing and data conversion, comprehensive definition of the requirements, clear rules to perform such two tasks, as well as solid technological solutions implementing them, are still lacking in functionalities. Those specific issues can be a sensible starting point for planning the next GeoBIM integration agendas@en

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.@en

OGC CityGML is an open standard for 3D city models intended to foster interoperability and support various applications. However, through our practical experience and discussions with practitioners, we have noticed several problems related to the implementation of the standard and the use of standardized data. 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. This study explicitly pointed out the critical points embedded in the format as an evidence base for future development. A companion article (Part I) describes the results of the benchmark related to IFC, the counterpart of CityGML within building information modeling.@en

Among the digitalization processes which are being raised in Europe and in the world, the building permit process is seen as one of the priorities by municipalities, governmental institutions and standardization organizations. However, in current practice, the building permit issuing as well as the integration of geoinformation with BIM (GeoBIM) suffers from a number of complex sub-issues. These issues still remain and prevent the development of successful methodologies. In this paper, the building permit use case is explored within a project in close collaboration with the municipality of Rotterdam. A very specific case study in Rotterdam was selected as a starting point, which allowed us to develop the needed methodology for the implementation of an effective tool. In this paper we highlight the interpretation and formalization of regulation for building height, overhang and tower ratio. While these rules are specific to a zoning plan in Rotterdam, we believe that the methodology and encountered issues in formalizing the rules, applying the rules on delivered models and integrating various data sources (BIM and GIS specifically) are general to most building codes.@en

In both research and practice, data interoperability is considered essential to support a rising number of applications that need data from different domains. Therefore, standard data formats and models are developed by standardization organizations such as Open Geospatial Consortium (for the Geo domain) and buildingSMART (for the BIM domain). However, from practical experiences, problems were noticed (standards implementation and use of standardized data). Nevertheless, it was hard to discover what the most serious issues were and what was their reason. For GeoBIM (integration of geoinformation with building information models), the CityGML standard, by Open Geospatial Consortium, and Industry Foundation Classes (IFC) by buildingSMART, were considered and tested in this initiative. A sample of datasets in the two formats were provided. External volunteers were asked to import the datasets in tools supposed to support the standards, check relevant aspects for the use of data (geometry, semantics, georeferencing, functionalities), report on them, and re-export the datasets in the standard format. Other tasks were intended to describe and test georeferencing procedures for IFC models and conversion tools between CityGML and IFC. This benchmark was useful to gather best practices and data about the functioning of useful tools to manage standardized data. Common behaviors and potential problems were pointed out and the discussion about the use of standards was further pushed.@en

Industry Foundation Classes (IFC) is a complete, wide and complex open standard data model to represent Building Information Models. Big efforts are being made by the standardization organization buildingSMART, to develop and maintain this standard in collaboration with researchers, companies and institutions. However, when trying to use IFC models from practice for automatic analysis, some issues emerge, as a consequence of a misalignment between what is prescribed by, or available in, the standard with the data sets that are produced in practice. In this study, a sample of models produced by practitioners for aims different from their explicit use within automatic processing tools is inspected and analyzed. The aim is to find common patterns in data set from practice and their possible discrepancies with the standard, in order to find ways to address such discrepancies in a next step. In particular, it is noticeable that the overall quality of the models requires specific additional care by the modellers before relying on them for automatic analysis, and a high level of variability is present concerning the storage of some relevant information (such as georeferencing).@en

In this chapter, we start from the typical concepts from Geographic Information System (GIS): data representation, acquisition, querying and analysis. We follow with the transition from 2 to 3D GIS and describe open standards such as CityGML and CityJSON and recent advances on 3D geospatial simulations, computing and real-time GIS and Internet of Things (IoT). Then we discuss the discrepancies in information management and modelling with respect to Building Information Modelling (BIM) and the related open standard, Industry Foundation Classes (IFC). We highlight the difference between Cartesian engineering coordinate systems and geospatial coordinate reference systems, contrast the procedural geometry definitions of IFC with the explicit geometries of GIS and look at implementation mechanisms such as boundary representations and polyhedral surface models and describe the semantic Level of Detail used in CityGML. The section that follows describes relevant processes supporting integration such as georeferencing, conversion of formats using semantic and geometric approaches and linking of heterogeneous information. We also highlight interoperability challenges that stem from consistency and validity of data, by interpreting the results of a recent benchmark on interoperability of the most common involved data formats (CityGML and IFC). We close with a conclusion and perspectives on the future with case studies on geo-enabled building permit checking and geospatial artificial intelligence and machine learning.@en

The Industry Foundation Classes (IFC) cover a wide variety of subdomains in the construction industry. Model View Definitions (MVD) enable to specify a subset of the IFC schema to assess the content of a model for specific use cases and information exchanges. However, IFC and MVD paradoxically complexify the workflow since it requires a deep understanding of the schema combined with construction knowledge to carry out simple use cases such as quantity checking or data export. This gap between domain specific queries and their expression in a computer-readable language weakens the opportunities provided to the building industry by Building Information Modeling. Our research consists in the implementation of MVDs in a high-level programming language to extract data from building models, an assessment of the extraction results and geometrical processing algorithms to correct the explicit quantities and properties that are supplied as metadata alongside the elements in IFC building models. Geometrical processing can be used to reduce and eventually correct errors on property values. We use a generic geometrical representation of IFC entity instances and apply geometrical transformations on those to obtain geometrical shapes. Boolean operations are used to identify relationships between elements. Eventually, incorrect data values are corrected directly in the IFC models accordingly to the IFC schema. For instance, we authored an MVD to extract data pertaining to external walls from different IFC models and corrected the value of the IsExternal property of the models’ IfcWall entities. This use case is of great importance for the cost estimation of a thermal renovation on a building as it gives a good estimate of the outer surface area of the building envelope.@en

With the ever-growing digitalisation of the built environment, specifying information requirements (IR) is crucial to control the Building Information Modelling (BIM) data. However, the way of encoding these requirements is subject to a wide range of possibilities, making it difficult for the users to choose the most suitable method. The paper presents a comparative analysis of methods to define IR based on document study and expert group discussions. The study covers Data Dictionaries (ISO12006), Information Delivery Manual (IDM), IFC Property templates, Information Delivery Specification (IDS), Level of Information Need, Model View Definition (mvdXML), and Product Data Templates (PDT), as well as other, non-standardised methods such as Linked Data with SHACL. The comparison is based on criteria from the review of use-cases and covers aspects such as value constraints, properties of fields, geometry representation, metadata, expressiveness and dependency. The paper concludes that no single method covers all the discussed aspects, and selection should be made consciously based on a purpose. The results are relevant to information managers to understand the relations and differences between IR methods, suggest standardisation bodies a way forward to harmonise, integrate or differentiate the standards, and provide a framework for evaluating IR methods.@en

To support building permit issuing with automatic digital tools, the reuse of models produced by designers would make the process quicker and more objective. However, current studies and pilots often leave a gap with respect to the models as actually provided by architects, having varying quality and content. In this study, rather than taking a top down approach, we started from the available data and made the necessary inferences, which gave the opportunity to tackle basic and common issues often preventing smooth automatic processing. Specific characteristics of the IFC models were outlined and a tool was developed to extract the necessary information from them to check representative regulations. While the case study is specific in location, regulations and input models, the type of issues encountered are a generally applicable example for automated code compliance checking. This represents a solid base for future works towards the automation of building permits issuing.@en

Standardised data formats and data models are essential for data integration and interoperability, which in turn adds value to data by allowing its reuse in multiple contexts. For this reason, in recent years extensive efforts have been focused on standards development. When representing the built environment, 3D city models and Building Information Models are particularly relevant, and their integration is now required to underpin use cases that cover the full life-cycle of a built asset, including design and planning as well as operations and management, and to support legal applications such as cadastral systems. For those kinds of data, CityGML by the Open Geospatial Consortium and Industry Foundation Classes by buildingSMART are the most popular reference standards. However, many users report, often through informal channels, the difficulties of working with these formats. This paper summarizes the outcomes of the GeoBIM Benchmark 2019, a scientific initiative funded by ISPRS and EuroSDR to collect insights into the most relevant issues encountered in the management of CityGML and IFC within existing software. Alongside data management (import, visualisation, analysis, export) problems, issues of particular consequence in terms of integration relate to georeferencing IFC files and the conversions among the two kinds of formats and models. Thus, the benchmark was designed to explore these tasks in available software. Following analysis of the benchmark results, a key outcome is the impossibility to find clear patterns in the behaviour of tools, which consequently means there is no consistency in the implementation of standards. Although the results could seem disappointing, the criticality in managing these standards as they are was described and this awareness can be the starting point for further research or further standards development. Finally, this project was useful to gather a wide community around this topic, and the discussion about the GeoBIM-related issues was definitely pushed. @en

The Industry Foundation Classes are a prevalent open standard to exchange Building Information Models. In such a model, geometric representations are provided for individual building elements along with semantic information, including a significant amount of properties related togeometry and explicit topological relationships. These relationships and quantities introduce redundancies and often inconsistencies as well. Moreover, they introduce complexity in down-stream processing. Combining multiple aspect models into a single model has non-trivial consequences for the connectivity graphs. Programmatic mutations are complicated because of the relationships that need to be updated as a result of changes.In order to alleviate these issues, this paper provides a theoretical frameworkand implementation for both validating and inferring semantic and topological con-structs from the geometric representations, rooted on Egenhofer spatial predicates and extended with the IFC modelling tolerance. Combining these two concepts, wall connectivity is equivalent to the intersection of the wall representation boundaries, where a boundary is not a surface, but rather a hollow solid with a thickness derived from the modelling tolerance.The algorithms presented in this paper are implemented in fully open source software based on the IfcOpenShell software library and the CGAL computational geometry library using Nef polyhedra. We provide a formalization of space boundaries, spatial containment and wall connectivity relationships. The validation and inference rules are applied to a public set of building models. We conclude that exported models have geometric flaws and that several relationships can indeed be inferred by means of generic geometric intersection logic.@en

Multi-disciplinary three-dimensional representations of building designs are available in BIM. However, thermal analysis often remains a manual task due to disparities in modelling: In IFC, buildings are decomposed into sets of elements with individual solid volumes. Thermal analysis requires interfaces between pairs of adjacent spaces. In this work, we present an end-to-end solution for thermal analysis on IFC building models. We derive thin-walled thermal interfaces from architectural building models using voxelization. Neighboring spaces (separated by wall volumes in IFC) are touching after aligning to the voxel grid. The resulting mesh is converted into OSM files for OpenStudio/EnergyPlus. This paper provides an implementation, discussion and initial validation. The algorithm depends on a minimal amount of information and favors robustness over accuracy, algorithms on voxels are robust. It is suitable for early design feedback and partial or imperfect scan2bim models.@en

In this paper, we discuss an automated procedure to automatically analyse and extract domain specific construction information from IFC building models. More specifically, we were interested in extracting location potential placement sites for thermal bridges between balconies and their neighbouring floors. For this aim, we developed a web-based platform where balconies could be manually selected to be analysed at a platform which was built upon open-source computational frameworks such as OpenCascade and IfcOpenShell. Moreover, steps to automate classification of balconies and adjacent floor, without manual selection, are discussed along with shortcomings and possible solutions regarding these classifications. The output consisted of elementary attributes such as geometrical coordinates, mass and volume as well as more sophisticated attributes such as the cantilever direction and the equality between balconies. These attributes can then be embedded in practical, day to day, operations.@en

The buildingSMART Technical Roadmap, published in April 2020, was the start of multiple modernization efforts for buildingSMART Solutions and Standards. The modernization, modularization, and normalization of the Industry Foundation Classes (IFC) is one of the priorities. A taskforce has been working on restructuring the core of IFC for the IFC 5 developments. The following topics are discussed and researched (a) modularization of IFC (b) normalization of the IFC object trees and relations (c) language independency of the base data structure (d) modernization of the deployment tools and procedures for maintaining IFC. This paper reports progress on all these topics. The normalization of the object tree is an integrated effort that involves changes in the use of objectified relations, property sets and predefined types. The modularization provides interoperability between domains and a solution to easily support incremental updates in software implementations. This so called 'late binding' approach and the consequences on the IFC schema have been researched and reported in this paper. The paper is a progress report with an overview of considerations and work done so far. It will end with a discussion chapter about consequences of the modernization work and a call for participation in further developments.@en

Recent progress in computer vision and the pervasive use of Building Information Models (BIM) in the construction industry provide countless opportunities for decision making in architectural design. It allows capturing real-world geometrical data for assessing design options, such as windows products for replacement on the façade of an existing building. However, capturing information from the real world is a tedious task that involves data acquisition followed by costly processing steps. In this study, we focus on using a single 2D picture containing simple building elements in their context to generate a semantic 3D model of these elements. To that aim, we trained a detection neural network whose input constituted of labeled photographs containing windows. After training, the model is able to locate and segment elements of interest on unseen new data. With the use of Computer Vision methods, we derive accurate geometric outlines suitable to reconstruct photorealistic three-dimensional BIM models.@en

In current BIM standards and today's BIM practice, drawings and models are used side-by-side. While respecting the de-facto coexistence of models and drawings, the induced information redundancy results in challenges for proper information management. It is thus desirable to establish and maintain deep links between the model elements and the corresponding drawing elements, as this allows for bi-directional navigation across the model/drawing boundaries and enables accessing non-geometrie model information from the drawing. In addition, consistency checking and preservation become more reliable. The paper specifies the requirements and semantics of the linking mechanism and discusses different technical implementations. Major emphasis is placed on the concept of the Information Container as defined by ISO 21597 which allows to represent and exchange linked models in a vendor-neutral format, but alternative mechanisms are also investigated. The paper finishes with presenting a feasibility case study.@en

Traditional building information modelling (BIM) education emphasises the tools and the modelling rather than the analysis of the model. Rather than simply provide training for proprietary software, university BIM education could support innovation through the development of standardized OpenBIM tools, data and processes, supporting students to analyse their own models and learn from BIM rather than simply learn howto BIM. This paper presents a family of courses, wherein; (1) postgraduate students in the autumn, develop OpenBIM tools and processes, that are used in the spring to provide rule checking on (2) the BIM modelling for an undergraduate course and (3) the design models of a post graduate multidisciplinary course. Feedback from the tools is integrated into the students’ personalized course homepages. An open web-based platform is proposed where students in the design and modelling courses receive feedback on their BIM from tools developed in the BIM tool and analysis course.@en

Gedetailleerde modellen van gebouwen (BIM) worden als waardevol gezien in combinatie met geo-data. Met behulp van virtuele modellen van nieuwe gebouwen (of delen ervan) kan de impact van scenario’s worden doorgerekend op bijvoorbeeld energie, geluid of wind. Al tijdens de ontwerpfase kan rekening worden gehouden met planologische beperkingen, als deze informatie beschikbaar is. Het BIM kan na oplevering van het bouwwerk worden gebruikt als gebouwgebonden informatiedossier voor domeinen als energie, circulaire economie enzovoorts. @en

In this paper we document our approach on applying Behaviour-Driven Development (BDD) and Continuous Integration (CI) from the software industry to the construction sector. We have provided a freely available open software toolset for the application of rules in the Gherkin syntax to an IFC building model. A prominent aspect of BDD and contrary to mvdXML, the formalization of rules in plain-test human-readable scenarios provides a basis for collaborative formalization of rules among stakeholders. At the same time our approach includes imperative program code that is fully extensible to incorporate for example external data sources and geometrical reasoning. Runnings test on every model revision (the CI concept) as opposed to, for example, upon model delivery ensures a proactive approach to compliance. Reusing existing open source frameworks allowed us to build a comprehensive solution for continuous and automated model checking, visualization and reporting in several hundred lines of program code.@en