Specialised metadata for laser scanning carried out by Bristol University

Date of capture: 23rd - 27th May 2004, 7th - 16th June and 11th - 15th September

Scanning system used (with manufacturers serial number): Minolta 910 Serial #:2501046 - resolution (?0.008 mm) and captures 307,200 points in 2.5 seconds (in the slow mode)

plus another long range laser scanner from Durham Geography/Geology dept

Who carried out the survey: Bristol University Graphics Group

Survey number (if there was one): N/A

Point density on the object (with reference range): Varies per stone.

Weather during scanning: Dry. Scanning was cancelled on wet days. Scanning was conducted either at night or in a dark tent using fluorescent strip lights to get a constant illumination. A forensic tent was erected over the stone to exclude light during the scanning process and two fluorescent tubes were attached to either side of the scanner head to provide a uniform light source.

Methodology:
 Durham Geography/Geology dept. conducted a long range scan which was calibrated to GPS coordinates. This poor resolution scan was used to align our high resolution scans to a meaningful coordinate system. The rocks were scanned in at night or in a dark tent using fluorescent strip lights to get a constant illumination. Sketches were made of the rocks and these were used to track where the individual scans were taken so as to ease the registration of point cloud data.
 
 Stone 11 of Castlerigg Stone Circle was scanned at a higher resolution than the other stones in the circle as this is the one stone where rock art has been recorded in the past. A lens with a resolution of 0.068mm was used for the external face and sides of the stone, and a telephoto lens with resolution 00.39 was used for the internal face where the spiral motif was recorded in 1995.
 
Description of registration method: GSI's standard point cloud registration system.

Index plan showing data collected with individual scan points named: Scans of these plans/sketches are available on request.

Any scanner specific information: N/A

Precision of measurement: Varies per stone.

History of ownership/rights of/to the data: Data is owned by Durham University Archaeology Dept. Bristol University Graphics Group reserves the right to use the data for internal and demonstration purposes.

Software used (if any): GSI Studio 2.3 & 3.0

Preliminary pre-processing:
 - Scans were colour balanced (simple normalising of RGB data) between scans per rock.
 - Scans were trimmed of onion-skinning and extraneous data.
 - Trimmed, individual scans are in separate .xyz files in a folder for each stone for registered data. Prior to the aligning to GPS data.
 - The 'final' .xyz file that is aligned to the low resolution scan from Durham geography department is a composite of all the scans (at the time this was the only way to perform such a transform in GSI).