The world-famous Stonehenge has been laser scanned in unprecedented detail, revealing 71 carvings of Bronze Age axes not seen in more than three thousand years.

The task of further examining this ancient structure, to discover more about it, was awarded to ArcHeritage, part of the York Archaeological Trust in the United Kingdom, as part of a project commissioned by English Heritage.

The laser scan used point spacing of 0.5 millimetres, and resulted in an enormous data resource of 850 gigabytes. Preliminary examination of the meshed models identified individual tool marks over 5,000 years old, but it was evident that the data contained more prehistoric artwork carved onto the surface of the stones.

The team decided to visualise the original point-cloud data and created a workflow using Bentley Pointools. The use of Bentley Pointools on this project enabled large datasets to be loaded, facilitating an examination of the full resolution data. The software’s shading function was instrumental in visualising the most subtle features, which resulted in the discovery of the subtle, Bronze Age carvings.

“We needed a software solution that would handle and visualise vast quantities of survey data,” said Marcus Abbott, a member of the ArcHeritage geomatics and visualisation team. “Bentley Pointools is capable of loading both 3D mesh and point-cloud data. The discovery of unrecorded prehistoric rock art on the stones was first realised in Bentley Pointools.”

Richard Zambuni, Bentley global marketing director, geospatial and utilities, said, “Stonehenge is one of the world’s great buildings surviving from prehistory – it is not fanciful to call this amazing public building ‘infrastructure,’ and although we know very little about how this structure was designed, constructed, and used, cutting-edge infrastructure software such as Bentley Pointools can be used to give us more insight into this astonishing edifice.

“The layering and shading functions in Bentley Pointools allowed carvings of Bronze Age axe heads and daggers that were invisible to the naked eye to be visualised, and provided sub-millimetre accuracy to the archaeologists documenting Europe’s greatest Stone Age building. It is truly gratifying to see Bentley Pointools used on such an exciting undertaking.”

The discovery of the carvings at Stonehenge was realised through the team’s use of Bentley Pointools’ Plane Shading function to create a greyscale band 7.5 centimetres wide. This band was moved at 1-millimeter intervals through the data. As it moved, it created a high-quality rendering of the plane shaded image. The team repeated the process 75 times to complete a full colour-change for every point in the data. Depending on the position in relation to a pre-set camera plane, each point was assigned a greyscale value, allowing very subtle features to be visible. When the images were combined into an animation and played back, the carvings, which were invisible to the naked eye, were seen fading in and out.

It was only through Bentley Pointools’ powerful visualisation capabilities that this eroded prehistoric artwork was discovered. Once the extent of the carvings was identified, the team deployed the measuring and point location tools to accurately plot the carvings to the Ordnance Survey grid.

A case study on the ArcHeritage Stonehenge project is available from Bentley here [PDF link].