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RCAHMS said the ruins were difficult to survey using conventional methods.
Instead its surveyors used a laser scanner to build up a detailed 3D picture of the external walls from below. Several scans were made from different angles.
Engineers will use the 3D images to measure the size of gaps in the castle’s stonework.
The information will be used by the National Trust for Scotland (NTS), which owns Canna, to aid in its conservation.
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See the full story here: http://www.bbc.co.uk/news/uk-scotland-highlands-islands-14837405
