Building information Modelling (BIM) is one of the most fundamental changes to affect the global construction industry. The growing worldwide adoption and implementation is providing powerful data-based modelling, visualisation, analysis and simulation capabilities, that are revolutionising all aspects of the construction process.

The leading software fuelling this growth is Autodesk Revit. Purpose-built for building information modelling (BIM), Autodesk®, Revit® Architecture helps architects and designers capture and analyze early concepts, and then better maintain designs through documentation and construction.

The current perception has been that BIM can only really be applied to new build projects. However as a result of the economic downturn, new build instructions are few and far between.  In their place retrofits on existing sites have become a popular, if not the unavoidable choice.

This has created a demand to model existing buildings in Revit and a need to overcome the inherent problems that are associated when modelling complex ageing buildings and structures.

Creating a Revit model of an existing site using traditional survey methods can be a very costly and time consuming process.  Whilst a detailed measured building survey makes this process much easier, even this may omit vital returns of walls and roof detail.

Using normal survey techniques the surveyor would need to draw up external elevations for every face of the building and the roof. Then a detailed internal survey would be carried out to produce floor plans and a survey of any internal walls/columns/ roof structure.

Once the surveyor has produced these plans, they would be sent to an architectural technician, who along with lots of photos would use this as the basis to build his Revit model. The entire process is very time consuming, involving much duplication and prone to error.

To overcome this Digital Surveys working with the _Space Group have been developing new methods using the latest 3D laser scanning techniques, to streamline the process thus making it a more accurate and cost effective alternative.

The first live project to benefit from the new Scan to Revit services offered by Digital Surveys, was the Skegness Academy in the UK. The Academy is undergoing a £20 million new build and refurbishment of the current site and an accurate as built model was required to form the basis for all future works.

The scanner allows every minute detail to be captured and proved extremely useful in the roof area where every joist/ purlin/rafter was captured, as well as internal ventilation, ducts and services.

Laser scanning is becoming the preferred method for as built data capture and although it is well established in the offshore industry, the construction sector has had a slower take up.

This is due mainly to a lack of understanding of the technology and the many different software and hardware file formats. Laser scan files are also very large due to the sheer amount of data captured. To work with them requires additional, often costly plug-ins that allow the data to be managed efficiently in CAD programs such as AutoCAD and MicroStation.

Unfortunately at the time of writing no effective plug-ins for Revit exist, although it is rumoured that native support will arrive in the 2012 version. In the interim Digital have developed routines and workflow to enable smooth transition until Revit point cloud support is launched.

To begin the modelling with Skegness, the point cloud was brought into AutoCAD using the Pointools Model (www.pointools.com) plug-in. Next slices were cut through the point cloud at each floor level and drawn around. By snapping to the point cloud a very accurate floor plan was created which was used as the basis for the Revit model.

Digital have also partnered with PointCAB (www.laserscanning-europe.com). PointCAB have developed software which can interrogate the point cloud data and converts it to a scaled image. Point-Cab is the first application that automatically generates elevations and sectional views. By applying their Crystal Clear View Technology, Point-Cab is able to create clear and dimensionally accurate images directly from the scan data.

Using PointCAB, ortho rectified images of each elevation were generated and placed into Revit in their corrected locations. These dimensionally accurate images could then be quickly traced round with Revit families.

With a traditional survey you are limited to the number of sections that have been created. With laser scanning and PointCAB you can quickly generated as many sections as you want at the click of a button to easily build up the 3D structure.

For Skegness Digital also utilised Faros Webshare Server Software. This creates a 3D view from every scanner setup similar to Google street view. This can then be accessed via the web and has become an invaluable tool for project members to view remotely and check the finer details of the building without ever having to return to site!

Using 3D laser scanning drastically reduced the time on site to carry out the survey by over 50%. It also captured a wealth of extra detail such as the internal services which although not needed by the architects, can now be passed onto contractors to assist in the rerouting of pipe work and ducts.

James Austin senior Architect at _Space group commented:

“Working with Digital Surveys was a good experience and we were very pleased with the work they undertook. The information, received in this format, is enabling us to work in new ways on the project, it is a totally different approach using laser Scan technology.

Laser scanning is allowing retrofit BIM projects to become a cost effective reality.  It should be noted though, that the scanner is not a magic solution, but just another tool at the surveyors disposal and only as effective as the operator using it!

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