Geomatics and Archaeology

The capture, processing, analysis and presentation of geospatial data

A person surveying a ditch with a GPS

Measured survey
GPS

GPSAt Cotswold Archaeology we use Leica Global Positioning System (GPS) instruments to capture spatial information for site plans and earthwork surveys. Digital measured survey complements hand-drawn and written records to form part of the primary site archive. It allows for accurate site plans to be produced and edited quickly, which is crucial for informing excavation strategy and providing a snapshot of site progress for managers, curators and clients.

Total Station

Total stationTotal Station survey produces results to the same degree of accuracy and precision usually associated with engineering specification and allows for survey in a built environment where satellite signals are obscured by tall buildings. The instruments are often deployed on burial sites where the recording of grave goods requires a greater level of accuracy than can be consistently achieved with a GPS instrument. Total Stations are also used in conjunction with other measured survey methods such as photogrammetry for historic building recording.

From site to office

The data captured on site is quality assured, processed, analysed and presented by our in-house Geomatics team. Our post-excavation team will then assign archaeological phases (e.g. late Bronze Age, early Iron Age etc.) to the recorded features using dating evidence provided by the finds recovered during the excavation, and careful stratigraphic analysis. Once assigned, the phases are exported from an access database and joined to the spatial data (the features) in GIS to generate phased plans and spatial distribution plots.

The phased plans are vital for providing a visual account of how the site has changed over time. The Geomatics team are able to provide individual plots of each phase of the site ready to be used by the Illustration team to produce report and publication figures.

Spatial analysis

Using GIS software we provide a number of valuable outputs for the interrogation and illustration of site data. These include spot date plans, contour maps and artefact distribution plots for spatial analysis.

You can view this article as an interactive story map that shows the use of GIS in action.

Check out these stories from our Geomatics team

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Structure-from-Motion: Photogrammetry at CA

At Cotswold Archaeology we use photogrammetry to create measured, textured 3D models at a wide range of scales, from recording small objects such as grave goods to entire landscapes using drone technology. This technique provides powerful visual results for our clients and for you, the public. Many of our models are uploaded to Sketchfab where anybody can take a virtual tour of the artefact or site and learn more about it by clicking on the interactive information points. Take a look at the Boxford Mosaic below.

But what is Photogrammetry…?

Photogrammetry, often referred to as Structure-from-Motion, is a technique that uses a series of overlapping two-dimensional photographs to reconstruct a three-dimensional object or structure. The images are processed using powerful software that identifies common points across hundreds of photographs, producing thousands of ‘control’ points (or, common points). These common points, along with known values from the camera, are used to compute the position of the camera in 3D space. This ‘sparse cloud’ of points is then processed to produce a dense cloud of points. You can see the difference between the sparse point cloud and the dense point cloud in these images of the Boxford mosaic.

The software then creates a 3D polygon mesh between the points, and provides texture by draping the 2D images over the model. As an example, here’s what the mesh looks like for Boxford!

3D polygon mesh of the Boxford mosaic
3D polygon mesh of the Boxford mosaic

We can use these models to produce accurate, measured, two-dimensional ‘ortho’ images, which have been used to great effect for recording burials and historic buildings. In the image below, you can see how the smaller plan of this trench provides a basic location for the deposits and structures (the purple, red, black, and blue shapes), while the annotated ortho image gives more meaningful information on the colour and texture of the deposits, and the stone and brick detail for the wall footings.

2d ortho photograph of an excavation area in Bristol

When we use this technique for recording historic buildings, we are able to provide good quality visual information on materials and condition for our inhouse specialists and for clients – just look at the example below.

For more of our photogrammetry models, head over to our Sketchfab page!

Rebecca Havard

Check out these stories from our Geomatics team

A person surveying a ditch with a GPS

Geomatics and Archaeology

The capture, processing, analysis and presentation of geospatial data Measured survey GPS At Cotswold Archaeology we use Leica Global Positioning System (GPS) instruments to capture spatial information for …
Read More
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Is it a bird, is it a plane? Aerial Photography at CA

Not quite the angle we were after
Not quite the angle we were after…

When it comes to getting a bird’s eye view of an archaeological site, current-day archaeologists really do have all the toys. In decades gone by the most hi-tech equipment we were likely get our hands on was a beaten-up old theodolite (which required a master’s in geometry to use); and if you wanted aerial photography, you would have had to scale some scaffolding or head up a nearby building to get to whatever overhead vantage point you could. Strapping a camera to a kite or a balloon was even tried by the foolhardy (…ahem!).

These days we are spoilt for choice when it comes to options for getting those key images from above. The low-tech (and fairly cheap) option is an aerial mast. It doesn’t require a licence, or weeklong training, and at upwards of six metres tall it can certainly get you some excellent shots of your site. And if you have access to a sturdy vehicle, it’s possible to use fifteen-metre-plus camera masts!

The main components of the aerial mast are the telescopic mast itself, a motorised pan and tilt head with Bluetooth connection, a DSLR camera and a tablet to operate the camera from. The masts come in different varieties from monopods to tripods. For the safety conscious, guy ropes can be used to keep the whole thing secure. CA has been using camera masts for over 5-6 years on almost any site that deserves an elevated view with great results.

Aerial mast in use
Aerial mast in use
The Techie Bit…

The main components of the aerial mast are the telescopic mast itself, a motorised pan-and-tilt head with Bluetooth connection, a DSLR camera and a tablet to operate the camera from. The masts come in different types from monopods to tripods and, when required, guy ropes can be used to keep the whole thing secure. CA has been using aerial masts for many years on sites that deserve an elevated view, and with great results.

Site team photo, taken using an aerial mast

However, those with a head for heights, or who see themselves as the next Maverick, opt for the ultimate flying machine – the drone (or Unmanned Aerial Vehicle [UAV], for those who think this conjures visions of military war machines). A commercial pilot’s licence and a good amount of money are needed, but the end results are worth it.

The capability of these machines is truly awesome: the DJI Phantom 2, for example, can fly to an altitude of 11,000ft! However, UAVs are restricted to 400ft (122m) in the UK for safety reasons. There are an array of options to choose from, like the tiny ANAFI Parrot, which is 23cm long by 17cm wide, to the giant six-rotor drones. They have a range of cameras and other accessories that can be fitted to them for the job at hand, and they can even be fitted with a protective cage to shield them during use in hazardous locations.

CA has worked with drone contractors such as Aerial-cam, on almost every type of project, from excavations to earthwork surveys to historic building surveys. The capability they provide for recording archaeological sites at a detailed and contextual level make them an invaluable tool.

Photograph of an archaeological excavation site taken with a drone
Photograph of a Roman villa excavation site, taken with a drone

Not only can the cameras onboard provide static photos and film, but the imagery can be used to create photogrammetric models for analysing landscapes. To achieve this the site is flown in a grid pattern to capture overlapping vertical images across the site. The resulting photographic images are processed using specialist software to produce digital elevation models. But, more on that in tomorrow’s article!

Getting slightly different views of a site, by whatever means you choose, can be so rewarding for engaging people with a site. As archaeologists we often concentrate on recording at a micro level, but by using the aerial photography technology at our disposal we can see our sites in the wider world.

Jonathan Bennett

3D models of Clovelly Dykes hillfort, North Devon. Both available on SketchFab.

Check out these stories from our Geomatics team

A person surveying a ditch with a GPS

Geomatics and Archaeology

The capture, processing, analysis and presentation of geospatial data Measured survey GPS At Cotswold Archaeology we use Leica Global Positioning System (GPS) instruments to capture spatial information for …
Read More
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Further evidence for Iron Age occupation close to Ludgershall Castle

In March and April of 2021 Cotswold Archaeology undertook another excavation in the vicinity of Ludgershall Castle in Wiltshire, this time for Lovell and EDP, on behalf of Homes England, and Wiltshire Council. The results from this investigation indicate that occupation of the site occurred during the Middle Iron Age and Roman periods.

An aerial photograph showing CA's excavation of 2019 and 2021 in the vicinity of Ludgershall Castle
Middle Iron age grain storage pit during excavation
Middle Iron Age grain storage pit during excavation

The site, which is about 600m south-west of Ludgershall Castle, contained the remains of fourteen storage pits, further clusters of pits, some drip gullies and a trackway. The pits, which are believed to date to the Middle Iron Age, were probably grain storage pits and were found to contain pottery, animal bone, loom-weights and a copper object.  Some of the storage pits were up to 2.3m in depth and were capable of holding large amounts of grain, much larger then would be required for a single household. The number, size and scale of these pits suggests that a relatively large Middle Iron Age settlement once lay close to the site. The drip gullies may have been the remains of an Iron Age roundhouse, roughly 10m in diameter, but no dating evidence was recovered directly from these. The drip gullies were truncated by the two parallel ditches, roughly 5m apart, from a later trackway  that crossed the site during the Roman period.

Remains of possible bowl from Roman trackway
Remains of possible bowl from Roman trackway

A previous investigation by Cotswold Archaeology in November 2019 at Castle Farm revealed a Late Iron Age defensive ditch just west of the medieval outer earthworks of Ludgershall Castle. This was the first direct evidence found to indicate that Ludgershall Castle had originated as a prehistoric hillfort or defended settlement. The ‘hillfort hypothesis’ had been suggested earlier, as Ludgershall occupied an unfilled ‘gap’ in the general distribution of hillforts in this part of the country, and from the presence of ‘Celtic’ field systems visible on aerial photographs of the fields around Ludgershall. While not an especially prominent location for a hillfort, the village does occupy a low plateau which may have been attractive for early settlement.

Detailed plans of CA's excavations at Ludgershall Castle

The evidence from both of our recent excavations supports the hypothesis that there was an Iron Age hillfort and/or large settlement at Ludgershall, and that Iron Age occupation in this part of Wiltshire was more complex than previously thought.

Craig Jones & Ray Kennedy

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Anglo-Saxon bird brooch from Suffolk

Recent excavations by Cotswold Archaeology at one of our sites in Suffolk included the recovery of this stunning and quite rare form of Anglo-Saxon silver brooch, dating between the 9th and 11th centuries AD. When it was first recovered, the beauty of the brooch was dulled and masked by dirt.

Anglo-Saxon bird brooch before conservation
Anglo-Saxon bird brooch before conservation

Following a short spell undergoing careful conservation with Pieta at Drakon Heritage the brooch now gleams, and all of its glorious detail has been revealed.

Anglo-Saxon bird brooch after conservation
Anglo-Saxon bird brooch after conservation

The cast bird brooch has a fan-shaped tail with an interlaced knot motif, and is not readily paralleled in other known bird brooches of this date. It has a slightly puffed-out chest, with a broad, collared neck and a down-turned beak. Its eye is a simple ring-and-dot motif that is more typical of this brooch type. The wing, spiralling at the base, is narrow and rod-like. The bird’s legs are represented by simple stumps.

This brooch is categorised as a Weetch Type 30C of the later Anglo-Saxon period; it has neither the crested head of Scandinavian style bird brooches (Type 30A) nor the projecting cross of the Carolingian style (Type 30B).

We do not know how the brooch entered the archaeological record on a predominantly Roman site, as it was found in the topsoil. If it was lost, as is most likely, one can only imagine the dismay of its owner at losing such a fine piece of jewellery.

Ruth Beveridge

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Medieval Jug from our Jesus College Excavations

Pottery sherds are a frequent find on archaeological sites and they provide us with a considerable amount of information – what past peoples ate and drank, their daily tasks and wider trading networks, and their likely wealth and status. Our dig at Jesus College, Cambridge, has been no exception and we’ve uncovered this medieval jug, discarded in a refuse pit over 500 years ago and crushed in situ. Cambridge Archaeological Unit’s Assistant Photographer, David Matzliach, has created this 3D video so you can take a look for yourself:

As a point of interest, the purely decorative lead glaze on the vessel (which gives it the name ‘green glazed pottery’) would’ve been applied before firing at around 1000°C; the jug would then have been left to cool for upwards of 12 hours – not a process to be enjoyed by the impatient!

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