This post is about one particular use of laser scanner point clouds collected in the field. After several scans are acquired and are correctly georeferenced, using a total station, GPS or other systems, plan and elevation drawings of the scanned features can be drawn in CAD. Using the Bentley Pointools plugin for AutoCAD 3D, it is possible to display sections through the scan data in the vertical or horizonal plane (x and y axes). This appears onscreen as a thin line of the point cloud, which can be traced as polylines to generate CAD drawings of building plans and elevations, with details of faces and sections where necessary.
The great advantage of using this techique is that the onsite data acquisition is far faster than taking measurements by hand, and the data can be later exported back in the office. So it was that I worked with laser scan point clouds (scanned using the Faro Focus 3D) and a photogrammetric 3D model (processed in Photoscan) of the Monk’s Oven and Pump House at Calder Abbey , a site I have never visited, in order to produce elevation and plan drawings using CAD. Special thanks to David Andrews for his patient tuition in this!
These are the plans and elevations of the Pump House that I drew, with additional corrections and editing by David. (All images and drawings: copyright Historic England).
The annual CIfA conference, this year held at the University of Leicester, was a great opportunity to meet many engaged in commercial archaeology and in heritage associations throughout Britain and beyond. It was excellent to hear that many in the sector are advocating a greater need for training those at the start of their archaeological careers in specialist technical skills. The suggestion at the end of the Landscape Archaeology session that perhaps heritage bodies like Historic England and commerical units could engage actively with university modules in particular sounds like an excellent idea, or to offer training courses to suit a wide range of experience.
It was fascinating to see how geospatial imaging has been taken on board in forensic archaeology, and the popularity of UAVs (drones) is so much so that a session was dedicated to focussing on the use of these platforms as a means of acquiring archaeological data.
I particularly enjoyed the excursion to the Greyfriars area of Leicester city centre, and it was good to see how much ongoing conservation is happening. The Richard III exhibition was impressive too – housed in a well designed and modern visitor centre (though I must admit, as a Lancastrian, all bias had to be temporarily put aside!).
Many thanks to CIfA for funding my attendance and travel costs.
Earlier this week I travelled to photograph and laser scan a series of scheduled ancient monuments in the historic market town of Leek, in Staffordshire. Two Anglo-Saxon stone crosses stand outside St Edward the Confessor Parish Church, both with surviving carved decorations and one bearing a runic inscription – I’m hoping the 3D data we’ve gathered will be able to help identify what is written!
It was fascinating to hear of the local stories that are attached to these stones. Passersby were keen to point out the circular dent marks on the rounded shaft cross, which were allegedly caused by gunshots from Bonnie Prince Charlie’s soldiers as he passed through the town, with the cross being used as target practice.
We also recorded the late medieval market cross, sited in the town square. Quite a challenge as it is over 5 metres tall! Luckily we used an extendable tripod for laser scanning, using the Faro Focus 3D. For the photography, we attached the DSLR to a mast, and operated the camera remotely using a Camranger synced to my phone – very useful to make sure the shots were correct.
It was great to see how many people were interested in the work we were doing. It’s important to collect this data as a permanent record of these monuments’ current condition, as they are so exposed to the elements, their detailed carvings are slowly being worn away over time. The data will eventually be held in Historic England’s archives, once I have generated the 3D models and investigated the stones some more. I’ve already noticed some carvings and writing on the very top of the market cross, that’s impossible to spot by eye on site as it is so high up! This really highlights how valuable geospatial imaging techniques are to capturing such details, so we can record and study them in future.