Close-range, terrestrial and aerial 3D laser scanning were used to digitally document the Scottish Ten sites.
Laser scanning allows the 3D surface geometry of objects to be recorded in a digital form. A large amount of 3D data can be collected in a short time frame. Scanning can be done from a static position on the ground or from aircraft –when it’s usually known as LiDAR (Light Detection And Ranging).
Accuracy and resolution depend on the laser scanning technology used, which in turn depends on the scale of the surface to be scanned. Small-scale objects (around 1m across) can be recorded with a very high degree of accuracy (to 10s of microns). Scans of building facades and such structures may have an accuracy of 4–6mm.
Laser scanning benefits include:
ability to create a 3D snapshot of the as-built environment
accuracy of range – terrestrial systems can be used to scan objects from 50cm to 300m away with an accuracy of up to 4mm
close-range systems can be used to scan with sub-millimetre accuracy
rapid data capture – 1 million points per second
option to use point clouds with other datasets – e.g. traditional survey, GPS, high-resolution photography, thermal imagery, moisture mapping
varied point cloud data uses – e.g. condition monitoring, building information models, virtual reality tours and immersive experiences
How it works
A laser beam scans the object’s surface up to 1 million times every second, and the reflected laser light is used to compute the distance to the surface. This results in up to 1 million spatially accurate coordinates (or points) being collected every second.
The data is used to produce a ‘point cloud’, which accurately defines the surface geometry of the object. This is very useful in itself, but it can also be further processed to produce 3D models and outputs in other forms.
Scans must be taken from several angles to obtain optimum point cloud data. Complex objects will need to be scanned from more viewpoints to avoid missing important details. Scans must also overlap to enable them to be joined together.
To record the geographical position of the object, the Global Positioning System or Global Navigation Satellite System can be used to survey points within the scan. It can then be positioned accurately within a known grid system.
Types of terrestrial scanner
Triangulation scanners – used at close range to capture details on carvings and other small objects up to a few metres across in size
Phase comparison scanners – fast with a medium range (around 70m), so can quickly cover interiors where many scans are required
Time-of-flight scanners – with ranges of up to or over 300m, these can scan architectural objects, engineering structures and landscapes
Digital photogrammetry was regularly used in the Scottish Ten fieldwork to supplement laser scanning data. For example, it was used to record the complex carvings of Rani ki Vav and intricate inscriptions at the Eastern Qing Tombs.
Also known as Structure-from-Motion, photogrammetry is a means of creating a 3D point cloud using multiple overlapping digital photographs taken of the object of interest.
Traditionally, photogrammetry used a single stereo pair of photographs to create a 3D result. New processing algorithms means that multiple photos can now be used to generate a higher quality 3D representation.
A very accurate 3D point cloud can be produced using:
high quality calibrated camera sensors with reference targets and control
a systematic approach to data capture
Low-cost solutions – e.g. using mobile phone cameras – can yield quick 3D models. This technique has opened up 3D reality capture to a wider market.
The Engine Shed has been supported by a grant from the Heritage Lottery Fund. Thanks to National Lottery players, we have been able to create Scotland’s dedicated building conservation centre. It enables us to encourage understanding of traditional building materials and skills among the public and professionals and raise standards in conservation for traditional buildings.