Laser Scanning on Canna
8 September 2011
Laser scans produced by an RCAHMS survey team are being used to help conserve a seventeenth century castle.
The National Trust for Scotland (NTS), who look after the island of Canna, are seeking to assess the condition of the remains of the remote Coroghan Castle.
Coroghan is the oldest castle in the Small Isles and is reputed to have been used by the jealous “Black Donald of the Cuckoo” to confine his wife, preventing other men from seeing her beauty and trying to steal her away. Built on a rocky peninsula 25m above the sea and accessible only by a steep, narrow path, the castle is difficult to survey using conventional methods. Instead RCAHMS surveyors used a laser scanner to build up a detailed 3D picture of the external walls of the castle from below.
This innovative new equipment – a Leica Scanstation 2 – works by systematically scanning the visible surface of a structure with a laser. In order to get as complete a picture as possible several scans are taken from different angles, which come together to form a 3D image. The creation of this type of image, and the ability to measure at high speed to an accuracy of 6 mm from a remote location, make the scanner an invaluable surveying tool for RCAHMS. In the case of Coroghan one of the uses for the final 3D image is to enable engineers to measure the size of the gaps in the Castle’s stonework to inform future conservation work by the NTS.
While on the island RCAHMS staff also demonstrated their work to pupils in the island’s only primary school and to the local history group by scanning Canna House.
“We have been using the laser scanner for a year now to record different types of buildings and archaeological sites," said RCAHMS surveyor Georgina Brown. "Surveying a building in a location like Coroghan Castle has taught us a lot about processing the information created by the scanner. The data we’ve collected will provide key information to the NTS conservation plan for Coroghan, as well as adding to our own public database”
Images of Coroghan Castle and Canna House, including stills from the 3D laser scan, are available to view on RCAHMS searchable online database Canmore.
