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29-01-2008

BIM Data Exchangeability with New WFS for GML

OGC Workgroup for CAD-GIS-BIM Integration

 

In 2006, the OGC (Open Geospatial Consortium) created a workgroup aimed at achieving the integration of CAD and GIS technologies on the web. In doing this, the OGC continues to develop new standards and extend the ones that already exist. Spatial information can now be exchanged in a better way and can be used for multiple purposes in everyday life. This article shows how, thanks to the efforts of this particular workgroup, CAD and GIS technologies are being integrated, and what this will mean for the OGC in the near future.

 

By Eric van Rees

An example of a CAD-design that can be saved as a 3D-PDF and imported in Google Maps.


The OGC offers a platform to develop and test new standards that can be used to exchange spatial data. Its Interoperability Program aims to promote and guarantee interoperability for the spatial data user market. CAD and GIS technologies can be integrated by using open standards. It is now possible to exchange data from architecture, engineering and the construction industry (AEC) on the web and use it in a GIS environment where GIS operations can be carried out with the data. Object-oriented building information in 3D is currently available in Google Maps via tools such as SketchUp: this shows there is not just a need to show this kind of information in a bigger geospatial context, but technical possibilities that can make it happen. The OGC acknowledges that there is great potential for offering and exchanging building-specific data on the web. Making AEC data available in GIS environments has been tested, and the time has come to develop an OGC standard in this field.

 

The integration of CAD, GIS and BIM (Building Information Modeling) comes from a need to use building-specific information in a bigger spatial context for queries and GIS analysis. Geospatial information can be used in future urban planning when it comes to designing new buildings. That way, you can see how a new building will fit in with its immediate surroundings and what this will look like. Ideally, this exchange will happen via web services, which have the biggest range of users when using open standards.

 

Differences in CAD and GIS

The differences between CAD/BIM and the GIS world are great: when speaking about buildings, GIS is about the “outside”, and CAD about the “inside”; GIS is about small scale, and CAD about large scale; GIS makes use of  international coordinate systems, and CAD of local ones. More importantly, no web standards are available yet for CAD and BIM data, while for GIS there are many. OWS-4 created a solution for this deficit.

 

Web standards for GIS like WMS (Web Mapping Service), WFS (Web Feature Service), WCS (Web Coverage Service) and WTS (Web Terrain Service) have been established by the OGC. Exchange formats for WFS are GML and CityGML. The latter provides a rich semantic framework for representing urban features and their relationships with each other, but it has not been developed to serve as a medium for building activities and therefore is not to be used as such for AEC data.

 

A neutral data format has been developed to describe building-specific data, namely IFC (Industry Foundation Classes). This was done not by the OGC but by the IAI (International Alliance for Interoperability), which is connected to the OGC. IFC, which represents a semantic structure, is a data format that covers every phase of a building’s life cycle. IFC is supported for BIM by most large tools. However, it is not accessible via web services, as no standard was available for it at the time OWS-4 was formed.

 


The Freedom Tower will replace the WTC that was
destroyed at 9-11-2001.
A Web Standard for BIM

OWS-4 created an extension for the already existing Web Feature Service for GML with some BIM data options. The chosen data format to exchange IFC is GML. With this, it is now possible to save multiple georeferenced BIMs on a server, categorize, show and edit sub-BIM features, such as doors and windows, with queries. Retrieval of BIM features can happen with both IFC and CityGML. When it happens via IFC, a translation to CityGML is necessary. Although entire BIM models can be shown, sub-BIM transactions cannot be supported yet because of the complexity of minimal mutations inside a building, which has something to do with the richness of IFC.

In combination with CityGML, IFC can be used to display 3D buildings in a bigger spatial context and exchange them via web services. To do this, IFC needs to be shown in a viewer so the user can see the data as a physical 3D building. This data can now be exchanged with CityGML. Location-specific BIM data will be edited geographically (georeferenced), so it no longer has local coordinates but can be put into a GIS system that uses an international coordinate system. When being loaded into a GIS environment, BIM data is suitable for spatial analysis and the integration of CAD-information in GIS is a fact.

 




IFC: from MicroStation to Google Earth and Back Again

The OGC extension for WFS was tested extensively in the OGC during the second half of 2006; a demonstration followed. In a demo on the OGC website you can see how it is possible to choose a location for a field hospital in a large area, organize it with BIM and finally exchange it to Google Earth. With the extension of WFS it becomes possible to show multiple CAD data in their local context. Now you can determine which site has enough space to serve as a hospital.

A function can be appointed for each room of the chosen site once a site that meets all user specifications has been chosen. To find a place that can be used as an operating room, the ‘get feature’ option can be used to query the proper data in IFC or GML. After this, detailed building drawings can be made in a CAD system like MicroStation.


Scheme of OWS-4’s BIM-extension for GML.

 

The first step in doing this is to load 2D map information like aerial photographs into a CAD editor with a Web Mapping Service. Surrounding buildings in the chosen location will be loaded in the same CAD editor in CityGML with a Web Feature Service. The building itself will be loaded by WFS in BIM from a BIM server. Now it is possible to add features such as walls and windows in a 3D model.  This model can be translated, e.g., from MicroStation to a 2D model as a drawing design. By adding altitude to the drawing design, the user can export this 3D model as a 3D PFD and load it into Google Earth. Then the whole process of CAD-GIS-BIM integration can start again.

 

Eric van Rees (evanrees@geoinformatics.com) is editor of GeoInformatics. More information on www.opengeospatial.org.