If you work in the architecture, engineering and construction (AEC) industries then you may well
have heard the term “scan-to-BIM”, but what does this actually mean?
When people say scan-to-BIM they’re referring to the process of 3D laser scanning a physical
space or site, to create an accurate digital representation of it. That representation
can then be used for designing, assessing progress or evaluating options.
Now, when I first heard that I was feeling about confused as you are now so here’s
a step by step explanation of how the process works and the benefits it can bring.
Firstly it’s important to determine why you wish to create a digital representation
of a space and to be clear about what you will use that data for. If the team you commission
to undertake your survey know what it needs to be relied upon for, they can ensure you
receive a scan that best meets your needs.
In this example, we’ve commissioned a scan of a heritage building; the beautiful St James’ Church
in the heart of London.
The scanning process can in theory be undertaken by just one person, though this is dependent
on your site and the outcome a thorough risk assessment.
Using a standard tripod, a 3D laser scanner is attached. Scanners like the Trimble TX8,
demonstrated here, come in easily portable cases and weigh around 11 kilograms.
Before a scan commences, some key parameters need to be entered into the scanner’s touch
screen interface, but we’ll explain more about these a little later on.
To capture a digital representation of a space, a laser within the scanner case rotates at
high speed. As the invisible laser beam hits various objects or materials, their position
relative to the scanner and to other elements of your site or building is recorded as a
piece of digital data– this is known as a “point”.
When several of these points are collected they begin to build a highly accurate three-dimensional
digital picture of the space or site being scanned. A large collection of these points
is commonly referred to as “point cloud”.
Now it might sound obvious, but the more points you collect, the greater the accuracy of your
scan. This is commonly referred to as a scan’s “resolution”. There will
be times when you need the highest possible scan resolution, but this is isn’t always
necessary and it comes back to determining what you want to use the scan data for, right
from the outset.
The scanner automatically rotates during the scan process to capture the area being scanned.
It may perform a complete 360 degree rotation or a lesser turn, depending on the data to
be captured. The Trimble TX8 can reach points up to 340 metres away with its extended range.
The scan area and your desired resolution are all entered as part of that parameter
data we mentioned earlier on.
To give you some idea of the magnitude
of data collected during a typical 3D laser scan, the Trimble TX8 collects data on 1 million
unique points every second. That’s around 300 million points during a five minute scan.
3D laser scanning removes a large degree human error from the surveying process and enables
significantly higher volumes of data to be collected over a considerably shorter period
of time. This means that survey information can be relayed to project teams faster. It
also enables Surveyors to undertake more scans than they could have done previously.
The lasers used within 3D scanners are of no risk to people or animals and cannot materially
affect or damage a building’s fabric. This is a particularly important consideration
when working with heritage schemes, like this one.
A high resolution camera on the front of the Trimble TX8 scanner captures images of the
scan area, simultaneously to the laser scan. This enables the scan data to be “colourised”
at a later stage, creating a realistic render.
The laser beam emitted by the scanner can only travel in a straight-line from the spot
where the scanner is positioned. Therefore, to build a complete digital representation
of a site or building, multiple scans will need to be taken from a variety of locations,
ensuring complete coverage of the space.
This is another reason why it’s important to determine the objectives your laser scan
from the outset. You don’t want to scan more areas than are necessary.
So that’s the scanning part, but how do you bring that digital data that you’ve
collected out in the field, back into the office – for use by a project team potentially
in a building information modelling (or BIM) environment?
With your scan complete, the data captured can be taken out of the scanner on a simple
USB drive, like the one shown here. You can then insert that into a standard USB port
on your computer device.
What happens next depends to an extent on the scanning hardware you used, but for most
scanners you will need to open the raw scan data in a software programme that calibrates
it before it is ready for sharing with others or for importing into design authoring programmes
or into your project’s common data environment (CDE).
Having scanned with the TX8 in this example, we have imported our scan into Trimble
RealWorks; a powerful software tool that enables you to register, analyse and model from your
scan. The platform has a free browser-based viewer enabling your wider project team to
see and navigate around your scan.
The process of importing and calibrating raw scan data before its ready for use by a project
team is quite specialist and it’s advisable to commission your Surveyor or a qualified
party to undertake this process. We’re showing you the step here to better explain how the
complete process works.
Having a highly accurate three-dimensional digital representation of your building or
site available – in record time – is very powerful. You’re now more informed to develop
your design proposals, scope out your works or to verify the progress of works to date.
Those engaged with asset management quickly have a digital picture of their existing stock to hand.
Beyond the construction industry, 3D laser
scanning has many other applications – including for example in forensics, where it is used
to quickly and accurately document crime and accident scenes before such areas are re-opened
to traffic or the public.
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