Close-Range Scanning on Orkney
Colin Muir is a Stone Conservator, and close-range 3D specialist with Historic Scotland. He joined the Scottish Ten team in their second week on the island tasked with close-range scanning of all carved surfaces and inscriptions. This was to feed in to the main Scottish Ten project, as well as build on previous work undertaken by HS in the recording of these features. What follows are his experiences of the project -
Introduction
In August 2010 a diverse team of specialists from CDDV, Cyark and Historic Scotland assembled to facilitate the third project in the Scottish Ten series; the digitisation of the “Heart of Neolithic Orkney” . This is a designated World Heritage Site which encompasses Maeshowe chambered tomb, the Stones of Stenness, the Ring of Brodgar, and further afield, the Neolithic village of Skara Brae.
The Orkney digital survey was to be unusual in the scope of its vision. Unlike the previous Scottish Ten projects undertaken at New Lanark and Mount Rushmore the intention on Orkney was to record both the external forms and interior spaces of the monuments and place these in their topographical context. As well as this large scale data, it was considered equally important to digitally record the many small and faint markings of human activity that cover this rugged, stone-built environment. To enable the acquisition of such a wide range of 3D data, from the macro to the micro scale, required the full gamut of available technology.
Further Background
The Carvings
The carved markings to be recorded ranged from the enigmatic incised, and stone-pecked motifs of Neolithic peoples, through the elaborate carvings and runic inscriptions of Viking crusaders, to the graffiti left by intrepid Victorian tourists to the Northern Isles. These rare survivals highlight the innate human compulsion to mark our presence, and connect with a specific place and time. In so doing they can often communicate with us on a more personal level than the larger monuments and structures on which they are positioned. They are fragile, murmured messages from a deep, shared past.
Close - Range Scanning
In the context of the Orkney project close-range scanning enables a three dimensional snapshot of these faint and vulnerable carvings. They are of enormous social, artistic and linguistic significance, not just locally but internationally. The high resolution of the system allows fine natural features such as cracks and fissures to be monitored as well as recording subtle elements of the carvings themselves. Tool marks and cross-sections of incisions can help to establish whether the carver was right or left handed, which tool/s were used and whether the had been recently sharpened. It can also establish the presence of different individuals using different tool sets in the same location.
The Conservation Context
Surface monitoring using a deviation map to compare two scan epochs
The 3D scanning of many of these carvings has been carried out twice before; in February 2003 and October 2004 to enable comparison and analysis of the same surfaces over time, and to give early warning of areas experiencing erosion (loss of material) or accretion (deposits building up on the surface). This 3D technique is known as ‘surface monitoring’, and is of great benefit to the practical conservation of these artefacts by showing exact areas affected and thereby helping to identify the source of the problem. In 2004 it helped identify points of water ingress into Maeshowe, and thereby enable their location and effective treatment. The 2010 survey will provide higher surface detail than was possible previously, record more carvings and also covers a longer scanning epoch (the period of time between surveys) so has the opportunity to show more change. As such the 2010 survey is part of an ongoing continuum that helps to inform Historic Scotland’s treatment, care and management of this unique palimpsest of overlapping markings.
Objectives
The scan data acquired by the project is anticipated to have a wide range of end uses.
As well as surface-monitoring, mentioned previously, the data can be incorporated into wider coastal and land management planning. Particularly pertinent given expected rise in storms, flooding and sea levels predicted in the coming century. The survey will also act as a datum point from which future change can be measured and provides a record to enable accurate restoration should catastrophic loss or damage occur to a monument.
The models produced can also be used to carry out highly accurate ‘remote’ measuring and analysis. This enables researchers to investigate worn inscriptions or tool markings without having to physically go to the site. In the same way such data can be processed to provide online content for education and interpretation purposes on a global scale, such as Scottish Ten partner “Cyark” are commited to.
Finally the data can be used to 3D ‘print’, or CNC- machine physical replicas at any scale. These may be used as replacements for original elements that are threatened or deteriorating, as part of the conservation process. Alternately they may be created as tactile interpretational material for school children or the visually impaired to handle, or as site specific merchandise to raise funds for continuing conservation or research of the site.
Methodology
The dimensional form of the ‘Mainland’ (the largest of the Orcadian archipelago) was aerially scanned from an aircraft carrying a LIDAR scanner (Light Detection And Ranging). This equipment scans terrain to a resolution of metres. Next came long-range laser scanning, ideal for architectural facades and surrounding environs, then medium-range scanning designed for 360o degree capture of rooms and internal spaces, both working in resolution of mm. Lastly was close-range scanning, capable of capturing the subtleties of faint carvings and eroded surfaces.
This technology records down to sub-millimetre resolutions. All these technologies revolve around the projection of light (as a laser) and the recording of its reflection from a surface, to calculate a single point in three-dimensional space. So rapid are these measurements of X, Y and Z coordinates that hundreds of thousands of spatial points can be recorded in a matter of minutes or even seconds, creating a ‘point-cloud’. Repeated scanning from different locations by; mounting the scanner on a vehicle (LIDAR) , moving the scanner to different locations (long and medium range ) or moving a calibrated mechanical ‘arm’ (close-range) builds up the form with overlapping data which is then registered (aligned) together to create a singular surface.
Into the Underworld
It was a Sunday afternoon in August, waiting amidst travellers thronging Edinburgh airport that the realisation dawned on me that I would soon be leaving this all behind. Not just the location, but the people and the daylight. Over the next 24 hours I would have to adopt a nocturnal existence, then spend the next few nights, on my own, within an ancient Neolithic tomb, buried inside a hill. Over that time I was to digitally record the plethora of carvings that cover the interior of ‘Maeshowe’; one of Orkney’s most intriguing monuments.
Maeshowe
Maeshowe is one of the island’s star attractions, and is visited annually by around 22,000 visitors. This is all the more remarkable when it is considered that access is only by HS guided hourly tours, which are limited to a maximum of 20 people.
Maeshowe chambered tomb
The structure was built around 3000 BC and is considered the finest chambered tomb in north western Europe. It was to form part of a complex Neolithic ritual landscape, of interrelated monuments that includes the stones at Stenness and the Ring of Brodgar. Its entrance passage is aligned with the setting sun on the Winter Solstice, and its rays illuminate the central burial chamber. This designed phenomenon can now be observed remotely via a webcam within the tomb.
The hill’s true nature only became apparent in 1861 when it was finally broken into (through the roof) by archaeologist James Farrer. He was to discover within not only a spectacularly impressive Neolithic tomb with three (empty) burial chambers, but also evidence that he was not the first intruder into that sacred space.
Across the walls of the tomb were found a diverse array of runic inscriptions and figurative carvings dating from the Viking period. Later research was able to establish these dated from early January 1153, when Harald Maddadarson and his men broke into the tomb (also through the roof) seeking shelter during a winter storm. Over the three days they were to spend there they amused themselves by carving runic ‘graffiti’ over the walls, often displaying a wry wit and a ribald, earthy nature. Despite this diversion two of the men were said to have gone mad over the period, encompassed by those already ancient, mythic walls.
The Structure
From the outside Maeshowe is an unassuming little hill set amidst a low, undulating landscape overlooking the Loch of Stenness. It is slightly too symmetrical to appear entirely natural, yet merges gracefully into its surroundings. However, on entering the interior you are met with an impressively constructed 4.5m x 4.5m space.
Maeshowe interior with arm-scanner and laptop
Built from dry-bedded, flag-stone and clad on its exterior with clay as a waterproofing layer before being covered in turf, it is a sophisticated construction. Opposite the entrance, and on each side are square apertures that lead into three burial chambers, each roughly 2m x 2m. On the floor beneath them lie three expertly worked, ‘squared’ blocks of stone that once tightly sealed these openings.
The historic walls slope inwards, in narrowing incremental steps to a height of 4m (13ft) and are then topped by modern flagstone masonry and a concrete cap, installed in the early 20th century after archaeological excavations had been completed. The apex of the ceiling is around 4.9m (16ft) high.
Colin's Orkney Blog
Day 1
After sleeping as late as I could manage, the Monday was spent on last minute logistics. Transferring my equipment from the “Day team’s” van into my own, liaising with local HS colleagues on the island to arrange access to Maeshowe ‘after-hours’, and borrowing scaffolding and equipment from the local HS Monument Conservation Unit (MCU). This being Orkney in Summertime, daylight enabled tours to continue until as late as 8.45pm, so my ‘window’ for access was to be from 9pm to 8am.
Entry to the interior of Maeshowe is made through a 12 metre long by 1.1metre high stone-lined passageway; an uncomfortably long stoop for most people. Through this opening had to be pulled, pushed and carried all of the equipment required for the night; scanners, tripods, supplies, ’zip-up’ scaffold, rucsacs and ladder. A repetitive process that took half an hour at the start and end of each working day, and was a sure recipe for a backache!
3D scan model showing two different rune types used in the same inscription
For the initial hours of the first night I was joined by HS Photographer Mike Brooke, as he recorded me recording the Runes. The space inside Maeshowe is surprisingly spacious; until you fill it with two grown men in cold weather gear, two sets of tripods, scanners, cameras and their various transit-boxes. Add to that a floor full of electrical-cable spaghetti and we were literally tripping over each other! By about 1am Mike had the shots and video that he needed and after sharing a welcome cup of tea brewed on his primus stove, left me to the graveyard shift. Finally alone, I couldn’t help but ponder how the Vikings that whiled away their hours of refuge there, carving ever more elaborate engravings and inscriptions must have felt, enveloped in this dark place, surrounded by such sophisticated ancient masonry constructed thousands of years earlier.
It was a strange, chill quiet within the hill; until punctuated by the bleeps and chirps of the scanner’s audible ranging indicator. Sounding a bit like R2D2 snoring through a fitful slumber, its function is similar to a reversing-alarm on a car, and lets you know if you are too close or far away from the surface for the scanner to be operational. You get used to it as an accompaniment to the activity, though it will drive onlookers insane and eventually cause them to flee. Which is no bad thing, I have to admit.
Dawn brought light to the end of the tunnel, quite literally and by 8am I was packing up and lurching, blinkingly out into the dewy morning air. I was ready for my bed.
Day 2
The second night was a solo affair and went a little smoother having overcome some of the initial setting-up issues and worked out appropriate settings for the equipment the previous day.
Full moon over Maeshowe
The intention was to capture the highest inscriptions, so I had acquired a loan of a single stage scaffold from the local MCU to raise the scanning tripod a couple of metres from the ground and enable its arm to reach the carvings. The arm was operated from a low ladder so as to avoid standing directly on the scaffold platform. To have done so would have caused vibration to the tripod that acts as the system’s datum point, and produced ‘noisy’ or inaccurate data. Whilst this set-up was only required for two inscriptions, it proved effective, and the data quality was indistinguishable from that captured at ground level.
I was glad of assistance from the rest of the scan team in getting the additional equipment into the tomb as it was a lot for one person to lug each load the 150m from the van to the monument. One of the highest inscriptions rather unhelpfully translates as “Tholfr Kolbeinn’s son carved these runes high up” …yes he did! Carved at a height of 3.7m (12ft) an impressive feat, especially if he used his axe as other inscriptions in the tomb refer to.
Day 3
Kirkwall, 4am
By the third night I had a good grasp of the carvings remaining to be scanned and was thankfully unencumbered with ladders and platforms. The night flew past as I settled into a now well-worn routine. With the end in sight I was afforded the luxury of realising what a great privilege it was to have had this sacred location to myself over the preceding three nights. The space had a serene beauty in those small hours of the night and a stillness that was once undisturbed for over three millennia, as the world went on around it
After over twenty six hours of scanning, over the three nights, the last of the carvings at Maeshowe was finally recorded around 3am. By 4am I was returning to a sleeping Kirkwall that twinkled beguilingly across the Bay of Weyland.
Day 4 -House 7, Skara Brae
After the ‘gloom of the tomb’, I was looking forward to returning to a diurnal existence and a little summer sunshine. However, on Thursday morning I was to find myself ensconced in ‘House 7’ of Skara Brae.
House 7, Skara Brae - Looking out the entrance passage
Skara Brae is considered the best preserved Neolithic village in Europe, and House 7 is the best preserved building within that village. It still retains its original stone furniture and fittings, including an impressive stone dresser, panelled sleeping stalls and a central rectangular hearth. It also contains the highest concentration of carvings within any of the buildings on the site. Unfortunately all these features are very fragile, and have suffered from salt-related decay since being excavated.
Digital scan model of Neolithic carving from the edge of a bed slab
For conservation reasons House 7 was roofed over and sealed from public view in 2007 to create a totally dark, high humidity environment that would ensure harmful salts would not have the opportunity to crystallise and cause further damage to the vulnerable stone surfaces within. It is now essentially a man-made cave, by any other name. The day’s objective was to record the various Neolithic carvings in the house in their domestic context. They are found scattered over the edges of the stone bed stalls and other stone furniture within the structure.
Day 5 - Skara Brae - the Outside
The final day’s close range scanning finally saw me above ground and in glorious sunshine, at last. It felt strangely agrophobic though to be swinging the scanner arm around in the great outdoors, particularly whilst aware of the gaze of dozens of visitors to the site, arrayed around you.
Outside Skara Brae
Despite the sunshine, the day brought a few light showers as well. This necessitated rapidly covering the equipment with a giant golf umbrella until it had passed overhead. Although I had finally made it to the ‘outside’, the location of some carvings was to lead me back underground as I tried to squeeze the equipment into progressively smaller subterranean passages. Despite my best efforts there were some carvings that were situated in areas that were simply too confined to access, and these had to be left unrecorded. Perhaps in a few years technology will have moved on to the stage that the hardware will be compact enough to capture these areas too.
What next?
Now that the raw data had been captured, the long task of processing and refining it lay ahead. This is a procedure that would likely take many weeks and months to complete. My final tally of inscribed ‘panels’ alone, recorded at Maeshowe and Skara Brae, was 62. Each made up of anything from ten to fifty separate, aligned scans with a point to point resolution of 0.1mm. The high resolution, polygonised model of each these inscriptions will eventually measure many hundreds of megabytes. This material would all be added to the scores of long and medium range scans the rest of the team had amassed in their fortnight of work, which was now measurable in hundreds of gigabytes.
After much processing, the various layers of data acquired, from LIDAR through to close-range level, will eventually be assembled to provide a unique over-view of Orkney’s spectacularly rich Neolithic past (as extant in 2010). Whilst we are aware that the data set will have a broad range of applications, it is also certain to be utilised in the future, in ways that we haven’t yet envisaged.
