With an increasing demand of people moving into cities, the urban population is expected to increase by 75% to 6.3 billion in the year 2050. The current rate at which buildings are being constructed today is not sufficient to keep up with this growing demand. BIM has played a significant role in assisting architects, engineers and contractors to collaborate intensively, hence reducing the total time of completion and cost. The benefits of BIM have been widely recognized and most of it has already been implemented on actual projects. In order to keep pace with this growing demand, we need to further enhance our approaches to planning, design and asset management. Through BIM and GIS integration we can study and simulate effective urban transformation scenarios that paint a more complete picture over the future of our built environment.
BIM framework and GIS technology
Being from two different domains BIM and GIS were not designed to work together. After significant research and literature, it has become evident that a lot can be achieved by integrating BIM design processes with the location intelligence of GIS. In order to achieve this we need to establish a standard which takes into consideration both the limitations and advantages of these workflows and technologies.
IFC is a standardized, digital description of the built asset industry. It is an open, international standard (ISO 16739-1:2018) and promotes vendor-neutral, or agnostic, and usable capabilities across a wide range of hardware devices, software platforms, and interfaces for many different use cases. More about IFC, its uses and adoption may be found here. - buildingSMART
Why is IFC the way to move forward with this
The benefit of the Industry Foundation Classes (IFC) format is that it was designed to allow the inter-exchange of an information model without any loss or distortion of data. Being an open and neutral file format, it is not controlled by any individual software corporation and was in fact created to facilitate interoperability between different operators.
What are the advantages deriving from use of the IFC standard
Although BIM has been in play for a long time, the BIM softwares vary depending upon person, organization, and location. For overcoming this challenge IFC was designed to allow exchange of information through a standard format. Thereby resulting in the reduction of errors and costs due to rework. Also, a considerable amount of time can be saved with consistent data and information flowing from the design to maintenance phase.
What is the IFCsite
In IFC 2x3 and IFC 4, the IFCsite entity defines the cadastre or terrain, locates built assets and geographic features. It is usually represented in a local Cartesian grid system to suit their facility model. IFCsite has been further subdivided into two; small sites and large sites based on the size of the projects. The main reason for this division is that, the approach in georeferencing changes with a change in the size of the project in order to minimise error.
For georeferencing an IFC effectively, we need to define a set of parameters and assign values for these parameters. Here are some of the parameters used in IFCsite: RefLatitude, RefLongitude, RefElevation, LandTitleNumber and SiteAddress. IfcGeometricRepresentationContext can store a WorldCoordinateSystem, Precision and TrueNorth.
With the above-mentioned parameters, any point in the model can be georeferenced with precision.
What are the issues faced while georeferencing using IFC?
Some of the problems prevalent while trying to georeference an IFC are that positive values represent locations north of equator and west of geodetic zero meridian in IFC 2x3. Whereas in IFC 4 positive values represent locations east of the zero meridian.
But the major issue that still remains is that, IFCsite is still not used properly in practice and most of the models are wrongly georeferenced.
How to move forward then?
It is recommended that, while setting the real-world location for IFC files, use the latitude, longitude and altitude values in IFCsite taking into consideration the offset values given by the World Coordinate System of the IfcGeometricRepresentationContext for the 3D model. However, we still cannot expect these values to be matching the reality with the precision given in IfcGeometricRepresentationContext but the values should be easy to set to within a few meters of the real location. Also, incase the y-axis of the WorldCoordinateSystem in the IfcGeometricRepresentationContext doesn’t match the true North direction, the TrueNorth attribute needs to be set as well.
Other proposed actions:
Since a wide range of people are working on these softwares, there is a need for a set of clear, articulate and illustrative use cases in simple succinct language that is digestible by a broad audience. These use cases should clearly indicate the details of the software applications that are commonly used for BIM and GIS integrations and should provide a user manual on how to work with this integrated data.
While BIM standards have been well developed and established over the past decade there is a need to develop a similar shared vocabulary for BIM and GIS integration which should be made publicly available. These should be derived from existing standards and should use a shared resource for identifying synonyms. After setting standards for a shared vocabulary, a best practice document needs to be formulated that will recommend the use of 3-dimensional georeferencing and the level of precision obtained.
Geolocate using Studio 3DX
1)Alias Abdul Rahman, Umit Isikdag, Sedat Bakici
6) Open Geospatial Consortium, buildingSMART international
Built environment data standards and their integration: an analysis of IFC, CityGML and LandInfra, March 2020