SMR No.: ME015-012004-
Monument Type: Megalithic tomb - passage tomb
The Hag’s Chair is the popular name applied to one of the larger kerb stones forming the base of the Cairn T, the passage tomb on the summit of Carnbane East, Loughcrew. Located on the northern perimeter of the cairn the stone is shaped somewhat like an upholstered chair. The face of the stone is decorated with numerous cupmarks and cup and circles motifs. These decorations were recorded by Eugene Conwell in 1873, but today are barely visible. The rate of erosion of the face of the stone is unquantifed but there is no doubt that the decorative devices are gradually disappearing.
A cross engraved on the top of the stone allegedly relates to the use of the stone as a mass rock.
(Description provided by Tom Condit, National Monuments Service, DAHG)
3D Capture Method: Close range Scanning
3D Capture Description: The Artec EVA scanner is used to generate high resolution models of surfaces with small scale detail. The Artec EVA uses structured light to record. A forensics tent is used to create a controlled lighting environment and ensure measurement can proceed regardless of the weather when used outdoors. Scanning is undertaken with the fastest speed setting (15 frames per second) and with a minimum 400 mm depth of field. The data is recorded with sufficient overlap between scans to ensure easy registration.
- Resolution 0.5 mm
- Accuracy 0.1 mm
- Accuracy over distance 0.03% over 100 cm
- Texture Resolution 1.3 mp
- Colours 24 bpp
- Light Source flash bulb (no laser)
- Video frame rate 16 fps Exposure time 0.0002 s
Post-processing is done in Artec Studio 9 software: individual scans are edited, aligned, before a final surface is generated using global registration, fusion, and a small objects filter algorithm. If required, a textured surface can also be created. The model is exported from Artec Studio 9 as an .obj file. For dissemination purposes a 3D pdf of the model is generated using Geomagic Studio 2012.
Data Processing Software: Artec Studio 9 & Geomagic Studio