Laser scanning is a rapid, non-contact, accurate and objective method for digitally recording the surface of any object in 3D. The technology has been used for many years in the engineering and oil industries. More recently, as technologies have advanced and costs have reduced, the heritage industry has begun to adopt and adapt this methodology for a range of heritage assets. Laser scanning can digitally document the current condition of everything from archaeological artefacts to entire archaeological sites, heritage structures, buildings and landscapes.
A laser beam scans the surface of the object of interest. The laser reflects off the surface and returns to the scanner, where the time taken for the return signal to be detected is used to calculate the distance to the object. The scanner does this up to 50,000 times a second, depending on the model, and so very quickly collects a large amount of accurate data. Each return signal is registered as a ‘point’ and the collective 3D data is known as a ‘point cloud’. Point clouds are acquired from many positions around the target object and joined together in specialised software to generate the overall 3D dataset.
Range of scanners
There are a wide variety of laser scanners available to suit particular tasks. Simple desktop laser scanners are available for scanning small objects such as artefacts, while high-resolution hand held scanners can very accurately record objects at close-range. Tripod-based terrestrial laser scanners are suitable for scanning interiors and exteriors of buildings, archaeological sites and landscapes, at ranges of up to 300m from the scanner. Accuracy varies according to the model but can be sub-mm for scanners suited to recording small objects, to a few mm for those suited to recording buildings and landscapes. Aerial laser scanning is also achievable via a system fixed to the underside of a helicopter or small airplane. While aerial laser scanning is being carried out, hyperspectral imaging data can also be collected. Hyperspectral imaging covers the entire electromagnetic spectrum, and has significant potential for archaeological imaging and site prospection.
Within Scotland, Historic Scotland has the greatest resource in terms of laser scanning. HS currently owns six 3D scanners, capable of recording very small objects to large buildings. Historic Scotland has formed a partnership with the Digital Design Studio at Glasgow School of Art to develop laser scanning and digital documentation as a whole within the heritage industry. The partnership is known as The Centre for Digital Documentation and Visualisation (CDDV). CDDV will deliver commercial projects as well as focusing on research and development for laser scanning and other emerging digital recording technologies.
The Royal Commission for Ancient and Historic Monuments Scotland and AOC Archaeology Group own and operate laser scanners, and Orkney College have recently purchased a scanner for archaeological projects. There are several commercial companies based in Scotland who carry out laser scanning, but these are almost entirely within the engineering and chartered land surveying industries. Some of these companies do carry out projects on heritage structures.
It is worth noting that the majority of laser scanning carried out in Scotland is on a commercial basis. This is a reflection of the relatively high costs of equipment and processing software. However, Historic Scotland, CDDV and AOC do carry out research and development to further the practical applications of 3D scanning for the cultural heritage sector.
Currently, CDDV is working on a five-year project to deliver ‘The Scottish Ten’ (http://www.scottishten.org). This will digitally document Scotland’s five UNESCO inscribed world heritage sites and five international heritage sites (Wilson et al. 2011). The project marries scientific technologies with heritage conservation management. The primary aims of the Scottish Ten are to:
- Accurately record important historical sites for the benefit of future generations in Scotland and overseas.
- Maintain and develop Scotland as a centre of excellence in this field.
- Share and disseminate Scottish technical expertise and foster international collaboration.
- Provide digital media to site managers to enable them to improve care for the heritage resource.
- Recognise international Scottish cultural connections.
CDDV have also laser scanned large sites such as Stirling Castle and Rosslyn Chapel in recent years and has investigated the potential for 3D recording of historic iron structures (Wilson et al. 2010, Pritchard et al. 2009). Historic Scotland is beginning a rolling programme of digital documentation of all 345 properties in its care and works in partnership with academic institutions such as Glasgow University and Orkney College to laser scan archaeological sites. Historic Scotland has laser scanned several archaeological sites, including Ness of Brodgar and Links of Noltland in Orkney and Forteviot in Perthshire. HS also carries out close-range high-resolution scanning, such as on the skull on a knight excavated at Stirling Castle. This was the recent focus for ‘History Cold Case’ a BBC production which looked at virtual reconstruction of people, based on laser scan data and forensic archaeology techniques. Historic Scotland is also working in partnership with RCAHMS on the 3D documentation of Birkhill Fireclay Mine.
RCAHMS have commissioned the laser scanning of several Pictish carved stones and other monuments over a number of years. They have recently acquired a long-range terrestrial laser scanner to carry out survey projects.
AOC have been involved in the laser scanning of historic buildings, archaeological landscapes and artefacts since 2005, during which time several hundred sites of a wide range of types have been recorded in all parts of the UK, including the Western Isles and Orkney. In 2006, AOC initiated a Knowledge Transfer Partnership with the University of Nottingham to research and develop methodologies for laser scanning and other 3D survey techniques. This took the form of a two-year post-doctoral project based in Historic Scotland’s Edinburgh offices. The company has since continued to build on this expertise and has undertaken a wide range of recording projects for private individuals, commercial developers, architects and statutory bodies. Key AOC projects include: laser scanning of Rosslyn Chapel, Myrehead windmill, Caisteal Grugaig broch, terrain modelling at Keiss in Caithness (Cavers et al. 2010), object and close-range scanning, for instance, the Ormaig cup and ring-marked stones in Argyll (Cavers et al. 2008). Headland Archaeology wascommissioned to laser scan The City of Adelaide historic ship in 2009 on a commercial basis (Atkinson et al. 2009). This was carried out in advance of the deconstruction of the listed vessel.
Future for laser scanning in Scotland
In Scotland, the future is optimistic for laser scanning technologies. As costs continue to fall, the technologies are available to more people working in heritage science. More work needs to be done on promoting the range of benefits and uses of laser scanning and other digital recording technologies. CDDV hosts an annual conference on Digital Documentation, which seeks to spread the message on laser scanning and ensure Scotland remains at the leading-edge of this and other digital technologies.