Enterprise software integration is always complicated by different closed-source and proprietary systems that often do not communicate with each other well. Such difficulties are common to companies where digitization level is not high, the ones that outsource critical development projects to multiple vendors, and that only have a CIO and several system administrators in their IT department.
The more different software systems the company uses, the more file formats and process variations it has. Therefore, looking into a common denominator via open standards and file formats is reasonable.
In this article, we will briefly review open BIM standards and file formats for the construction industry commonly used today, especially when it comes to Building Information Modeling (BIM) representation.
Collaboration at the Core of Bim
Building Information Modeling started emerging in the 1970s. The concept is aimed at streamlining collaboration between parties engaged in design, estimation, simulation, construction, maintenance, as well as support of complex structures, for example a residential building, an airport, or a bridge.
BIM system should be capable of representing the physical and intrinsic properties of a building/structure as an object-oriented model connected to a database. In a BIM system, object definitions are mostly described parametrically: the objects itself and their relationships with each other are described with a set of interlinked parameters. These parameters can be easily modified, leading to recalculations in the final design forms and structure.
Thus the current trend is to move the collaboration from bid construction schemes to integrated project delivery systems, which allow everyone involved in the project access the same BIM models.
IFC & buildingSMART
Industry Foundation Classes (IFC) is an object-based data model and format that describes building and construction industry data. It was developed in 1995 by buildingSMART alliance, an international organization that focuses on improving data exchange between software solutions used in Architecture, Engineering, and Construction (AEC) industry.
Industry Foundation Classes is registered as an official International Standard ISO. Governmental clients that contract with construction companies often require a BIM system and BIM processes based on IFC open standards.
Thus, the buildingSMART model is a solid starting point for an internal digitization project that leverages BIM open standards and makes a company fitting for a big government project. Notably, UK, Singapore, Japan, the U.S., and the Nordic Region are the countries that lead in BIM adoption.
IFC File Formats
IFC files come in three major formats:
- (.ifc) STEP physical file — described in EXPRESS data definition language; text-based and compact
- (.ifcXML) XML-based file format — described in XML Schema 1.0, as defined by W3C; human-readable, but larger by ~300-400% compared to .ifc.
- (.ifcZIP) — compressed format consisting of either .ifc or .ifcXML files.
IFC BIM model is an object-based representation of physical objects. In case of a door, this would its constitutional material, geometry, various layers with different characteristics, including weight, light reflection, and others — all of which can be used later for cost estimation, simulation, and physical events modeling.
IFC format describes objects and interaction concepts in four different layers:
- Resource layer: the lowest level that consists of resource definitions that are used by definitions on a higher level
- Core layer: all definitions of entities here are basic and can be referred to independently or as a part of an object defined on higher layers.
- Interoperability layer: definitions of entities that are specific to a particular product and often used by multiple parties on a construction project within one domain.
- Domain layer: the highest level of entities, products, processes, and resources specific to a certain discipline. This objects are used in information exchange between domains with different specialization.
Image 1 -- IFC4 layers visualization
Industry Foundation Classes model is highly complex and covers a vast concept space; a single architect or software package does not leverage all available parameters and classes. A given process is usually restricted to a subset of specific classes with a limited number of parameters and resources needed for a specific job at a given stage of interest.
In the same way, export and import capabilities can also be restricted (or defined) by a subset of objects needed, for example, for traffic simulation or estimation of building a steel structural building facade.
Model View Definition (MVD)
A Model View Definition (MVD) describes a subset of IFC schema while also limiting file size and model complexity to facilitate data exchange between parties. MVDs identify what should be expected for an exchange to be effective. It helps systems on both ends; the exporter knows what is required and what is not required. There are a couple of standard MVDs.
Image 2 -- BIM general visualization
The Coordination View (CV) is the most commonly implemented definition of the IFC schema. It targets the coordination between the architectural, mechanical, and structural engineering tasks during the design phase. This was the first definition developed by buildingSMART tech team.
The main purpose of CV is to allow for BIM model sharing between major disciplines of architecture, structural engineering, and mechanical building services. CV includes elements for spatial structuring, building, and building services needed to coordinate design in these areas.
Image 3: MVD -- Coordination View Version 2.0
Coordination view can be re-editable by the receiving app; however, round-trip scenario for exchange is not defined.
IFC4 Design Transfer View
The IFC4 Design Transfer View targets all workflows based on models that are handed over to be performed in next workflows, also allowing for modifications of its content.
In addition to the exchange needs, the IFC4 Design Transfer View supports editing of interconnected elements. With IFC4, one can insert, delete, move, and modify building elements and spaces across different tools from different disciplines. An architect can send the initial design to an engineer who in turn can make structural changes and then return the model for further processing.
Internally, design parameters of higher levels must be preserved for those elements that span multiple disciplines, while applications must generate downstream geometry consistently in accordance with the parameters.
According to buildingSMART, here are the common characteristics of the workflow design transfer models:
- Source of the BIM information can be shared
- Basic parametric behavior, and thereby the intellectual engineering property, can be transferred
- Model ownership and responsibility for its correctness can be transferred
- Original model published as IFC4 Design Transfer model reflects the as-is status
- Receiver of the IFC4 Design Transfer View does not need to have access to all the pieces of the model
- Receiver of the IFC4 Design Transfer View can analyze and extract the information contained in a model
- Receiver of the IFC4 Design Transfer View can modify the model
- If the receiver suggests or demands a change, it can be made to the model directly
The characteristics indicate that such a system is ready for centralized BIM repository storage and multi-agent interaction based on a central database of building information.
IFC4 vs. IFC2x3
When you compare IFC2x3 with IFC4, one of the most important things to remember is that they are not directly compatible. The buildingSMART tech team removed a number of elements from IFC4, while several other elements were extended and improved upon. Therefore, one should use IFC2x3 Coordination View 2.0 (illustrated above on Image 3) to exchange data with old software solutions.
BIMSie: BIM in the Cloud
BIM Service interface exchange (BIMSie) its the standard API for BIM Web Services that enables BIM in the cloud and provides a way for communication between systems. It is a data-driven concept with a well-defined API structure. Having a standard API like BIMSie for BIM servers opens the possibility to develop software solutions that automatically work with every BIM server that supports the standard. As a result, BIMSie reduces software development cost, adoption, and interoperability within the industry.
LandXML: Land Development Industry Format
Infrastructure projects like roads, bridges, and railways demand slightly different types of data and parameters.
XML-based file covers the needs of such projects:
Transfers engineering design data between producers and consumers
- Provides a data format suitable for long-term data archiving.
- Provides a standard format for an electronic design submission.
Image 4 -- example from LandXML definition
IFC for Infrastructure
IFC-Alignment is the first extension project aimed at providing a standardized way of communication between engineering teams in infrastructure projects. Standard BIM models were not good enough for 2D spatial alignment, while IFC-Alignment serves as a solid baseline for IFC-Road and IFC-Bridge specifications.
Image 5 -- IFC-Alignment
With IFC-Alignment, the AEC industry achieved the following goals:
- Ability to exchange alignment information from planning and design to construction and asset management
- Ability to link alignment information to other project information, like cross-sections and full 3D geometry of construction elements (realized by upcoming IFC-Bridge and IFC-Road projects)
- Ability to query alignment information providing data like linear referencing for positioning
- Ability to access open data on alignment information in asset management databases
- Ability to map IFC alignment models to InfraGML (developed by OGC), and LandXML (latest InfraBIM version from buildingSMART Finland)
Importantly, IFC4, IFC-Alignment, and LandXML interoperate well. See the picture below as an example of their interoperability.
Image 6: IFC-Alignment interoperability
BIM open standards and file formats cover everything modern companies, architects, and engineers needed to design, collaborate, build, and maintain the majority of new buildings and infrastructure projects. Thus, more and more governments agencies are requiring BIM Level 3 support from the construction companies, as well as fully digitized processes based on open industry formats to develop their projects.
If you need help with your enterprise digitization strategy, we can help you unpack definitions, organize information workflow, and design systems that will support modern open formats in AEC industry.
About the Author
Pavlo Bashmakov is the Research & Development Lead @ Intellectsoft AR Lab.