It may seem like wizardry, but it is now possible to make highly accurate 3D scans of buildings – adding a new trick to construction professionals’ technical toolkits.
Creating an as-built record
One of the newest technologies to gain acceptance worldwide, and now in New Zealand, is 3D laser scanning that captures precise as-built records of buildings and structures.
3D laser scanning collects distance information of surfaces within its field of view using a line-of-sight laser. The information consists of millions of individual measurements that are combined to create a 3D collection of points, known as a point cloud. The point cloud represents the physical object, or environment, in digital space.
The typical data capture process involves a scanner successively positioned from a number of vantage points encircling a building or object. Each set-up and scan takes around 10 minutes to complete and can be performed by a single person.
Depending on the type and make of the scanner, objects can be scanned from several hundred metres away. Within a 25 m scanning radius, each scan point can be accurate up to ±2 mm. The scan resolution can be altered to provide greater detail as required, providing information as dense as one point of data for every 1 mm of surface detected.
Scanners can capture at speeds from several thousand up to one million points per second. The number of points captured determines the density of the point cloud created, which defines the model’s level of detail.
A key benefit of the 3D point cloud is the ease with which it can create useful models – the data can be exported to many common CAD, modelling and BIM programs to generate 2D CAD drawings or a 3D model. In this way, a single dataset can provide information for designers, engineers, contractors and operators, promoting greater accuracy and reduced variations.
Scope of use
3D laser scanning is useful for several applications:
- New build as-built surveys – to create traditional as-built drawings, frameworks for BIM models and stand-alone 3D models future-proofed for new design technologies.
- Existing building as-builts – where these are missing or inaccurate, 3D scanning can create accurate 3D models from which additions or renovations can be designed.
- Heritage building surveys – 3D scanning can capture the intricate detail of heritage buildings, useful in determining movement or damage or in providing precise details for rebuild or refurbishment.
- Civil infrastructure surveys – complete data capture from hundreds of metres away for motorways, high-rises, bridges or high-voltage plant, where other surveys might be unsafe or much less detailed.
3D scanning in New Zealand
In New Zealand, Auckland company asBUILT.co.nz has provided 3D laser scanning for a range of projects:
- As-built survey of Southern Cross Hospital in Christchurch to scan components of the building structure to assess structural deflections and damage.
- As-built survey of all buildings and grounds of Kawerau High School to create a 3D model of the entire facility, as well as the use of TruView photographic imagery to enable virtual tours.
- Scan to BIM survey of SkyCity Hamilton to produce a geometric Revit model for designers use on an upcoming refurbishment.
- Dilapidation survey of a central Auckland building to gain precise information on building defects before its demolition.
- Heritage building survey of St Matthews-in-the-city church in Auckland to capture the condition of the external façade for future on-going assessment, as well as the capture of site landscaping and surrounding buildings. Elevations and a site plan were produced from the point cloud.
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