CPD: Laser Scanning
This CPD is sponsored by KOREC. With a greater use of BIM and 3D models, laser scanning is becoming an increasingly popular method for carrying out building surveys. This CPD explores the benefits of 3D laser scanning.
KOREC delivers solutions which link office-based drawing with construction and surveying on site. Its laser scanning technology produces 3D models of both postconstruction and as-built structures, which can be introduced within the BIM process for surveys, visualisations and clash detection.
Part 1: What is a point cloud?
A point cloud is a set of vertices in a three-dimensional co-ordinate system. These vertices are usually defined by X, Y, and Z co-ordinates. Point clouds are most commonly intended to be representative of the external surface of an object.
Point clouds are usually created by 3D laser scanners. These devices measure in an automatic way a large number of points on the surface of an object, and often output a point cloud as a data file. The point cloud represents the set of points that the device has measured.
These can give an accurate measurement of work on site and can be used for surveying existing buildings. Scans can be carried out in RG B colour to produce a photographic image of the project at various stages through the construction process.
Part 2: How does it work?
To measure distances, the laser scanner uses a beam which is bounced back to the scanner by the object. The distance measured is given to millimetre accuracy through measuring the phase shift between the ending and receiving beam. At the same time as measuring the distance the
scanner also measures the horizontal angle. A mirror on the scanner deflects the laser beam in a vertical direction on the same object and this is decoded alongside the distance measurement.
Once measured, the distance, horizontal angle and vertical angle make up a polar co-ordinate. This is then automatically translated to an X, Y, Z co-ordinate for plotting. Phase shift technology is used to speed up the scanning process. This technology can scan up to 976,000 points per second, giving a richer dataset, which is better for both accuracy and quality.
Part 3: Example scan
Th is example demonstrates the process of scanning through a case study of a car park.
The scanner was set up so that it could see three target points within the building; these being easy recognisable points which could be used to locate the scanned data. The scan was then begun. This was repeated a total of three times from different points within the car park.
Each of these individual scans took four minutes. A point cloud with more than 160 million co-ordinates was created. In total it took 15 minutes to
scan the car park, including the time taken to reposition the laser scanner.
Once in the office the scan data can be transferred to a computer from the SD card located within the scanner.
Using software, the colour photography can be overlaid onto the point cloud data. The process of overlaying individual scans onto each other and stitching them together to create a continuous model can also be carried out automatically using software supplied with the scanner.
It is possible to create a 3D model of the simple car park space within 30 minutes. This allows a 3D rendered model of the site to be created for use from the start of any project.
Part 4: Integrating with BIM software
The point clouds generated through laser scanning can be imported into many BIM software packages.
When the scan is imported into Autodesk Revit it can be used for structural analysis, to create 2D plans and to create a 3D building information model.
The scans can be used to form outlines which can be traced over to create floor plans, sections, elevations and ultimately a 3D model.
Part 5: Scan sharing
Web-sharing programmes can be used to share the scans which have been created. Faro has a unique service which allows scans to be directly published to the internet. The scan data is then viewable using any web browser. Distance and area measurements can be taken from the scan as it is stored online.
Using FaroShare the laser scan can be shared online with the architect, the contractor and the client. This way of working is particularly good for live construction projects. It enables all those involved in the project to have live access to data as the build develops.
Part 6: Laser scanning benefits
Laser scanning has found a particular niche in heritage applications. Here it can be used to record buildings for restoration, excavation or scientific analysis purposes. Completed laser scans can then be used to create a 3D BIM model which can be stored for future restoration or refurbishment work. But heritage applications are just one of the uses of laser scanning which is gaining traction thoughout construction projects.
Laser scanning saves time due to its speed, ease of use and portability. Simple operation procedures mean the scan can be set up and running within minutes of arriving on site. The scanners are compact and therefore can be transported to and from site easily. This allows practices to take on more projects as productivity is much faster.
The process of scanning can also open up more opportunities for architects, as the scanning process is simple and can be done quickly on site with very little set-up or equipment. It allows an accurate 3D model of the project to be started from the initial surveying stage, which all members of the design and construction team can work from, reducing errors based around working from different data sets, drawings and models.