Aerial Photography and Visualisation for Built Heritage - PhD Portfolio by Kieran Baxter
Home Portfolio Showreel Publications Map Blog Contact

Tuesday, 22 November 2011

Hut Circle Topography at Bridge of Cally

"...traces of the others [hut circles] are very slight and were only recorded by oblique sunlight at about 1pm on a winters afternoon..." (RCAHMS, 1987)
This description prefaces the site record of Rochallie at Bridge of Cally which features two groups of hut circles among cairns and other features. The practice of waiting for snow and low light in order to see the topography of an un-excavated site is still widespread. With this in mind I set out to replicate the effect described at Rochallie using KAP and photogrammetry.

This first image is an orthographic colour projection derived from two KAP sequences. It is annotated with my interpretation of the hut circles and features based on the RCAHMS report and my own observation.

This second image is derived from the same data but with the colour removed and lit from a series of low angle lights. The three main hut circles can be seen in the center along with the other features. The photographs below give an idea of how difficult it is to perceive the topography in normal conditions, the more distinct hut circles and cairns are visible only on close inspection.

Hopefully these images demonstrate a fairly successful test of photogrammtery as a method for recording an obscured site. With hindsight I would attempt to capture the entire area in one pass for better coverage rather than going for multiple angles of such a low lying site. Although I was concerned that the software (123D Catch) would have issues with the similar grass texture this was no problem. Instead the main issue was recognizing the continuity from one frame to the next, something to consider when capturing in future.

Friday, 18 November 2011

Tealing Souterrain & Roundhouse Interpretation

A composite showing how the wooden roundhouse may have related to the excavated cellar at Tealing. This shot is made up of photogrammetry based on KAP at both Tealing and the Scottish Crannog Centre.

This has served as an important test of principles and brought up some of the concerns I can expect to face taking photogrammetry data to a final composite. In future more of an effort will be needed to keep render time down with basic efficiencies such as combining three lights onto the channels of one layer. I think that raytracing features such as shadows and ambient occlusion will only be possible if they are baked onto the surface- which shouldn't be a problem in these static environments.

I chose to orientate the crannog roof to keep the door to the sheltered north east. On reflection it would have been better to create a new door (the existing one was exaggerated from the original data anyway) in order to keep the patches of lichen on the damp northern side.

The internal structure is deliberately revealed using 2D transitions as I felt that rising the structure in 3D would in no way represent the process by which it was built. I think I would prefer the reveal to look manipulated than be misleading.

Tuesday, 15 November 2011

Near Infrared Photography at Laws of Monifieth

I was recently lucky enough to meet three kite photographers from the West Lothian Archaeology Group, John and Rosie Wells along with Jim Knowles, who delivered a lecture at RCAHMS advocating the use of low altitude aerial photography for archaeology.

Among many great examples of applications were aerial views which have been used to establish potential sites. Often buried features show up in crop growth with parch marks assotiated with disruptions in the soil. Healthy plants reflect infrared light so these parch marks can sometimes be observed by near infrared photography before they are visible to the naked eye.

As it happens digital camera sensors are highly sensitive to infrared light so any camera can be converted to capture these wavelengths by replacing an internal filter. John Wells very kindly lent me a converted Pentax Optio E35 capable of photographing wavelengths of 720nm. The results of my first experiments with infrared images at Laws fort and broch site near Monifieth are shown hear alongside standard visible light views.

It is clear why the site would make a good broch location with views for many miles across Angus and Fife. Tentsmuir beach is in the background of the fort in the visible light version. Notice out of the two fields in the background the darker but greener vegetation shows up brightest in the infrared

These photographs taken from a pole show the possible broch site which measures around 20m diameter. There isn't very much here in way of features showing through the vegetation although the snowy looking grass in the infrared removes some of the surface texture helping make out the topography. I find these unusual images visually striking as well as interesting to analyze and look forward to trying this out at different sites.

Monday, 14 November 2011

Alan Sorrel - How Traditional Interpretative Illustration Can Relate to Digital Visualisation

A landmark figure in archaeological interpretation, Alan Sorrel (1904 – 1974) produced many well cirulated paintings and drawings depicting British historical sites reconstructed. Of particular interest to my project are two illustrations of Jarshof, one depicting the iron age broch and village, one showing the later Norse settlements with the ruined broch just visible in the background.

Sorrel's illustrations are striking not just for their attention to detail but also for their consideration of mood and atmosphere. It is perhaps this sense of drama which has seen his work cited as a source of inspiration for both archaeologists and laypersons to the field. He gives the impression of a living site, a feeling I would like to instill in my own work.

It is clear that the reconstructed details are informed by the best opinions of archaeologists of the time. For example his drawing of Clickhimin Broch shows the 'lean-to' roof structure as interpreted by John Hammilton who excavated the site, along with Jarshof, in the early 1950's. Opinions change however and it is now considered more likely that the broch roof structures where more in line with roundhouse traditions (Armit, 2003).

Sorrel's reconstruction of Jarshof broch seems to be modeled fairly closely on the completed specimen of Mousa, a similar approach to the superimposition I intend to use for my interpretive film.

Another striking similarity to the kind of work I have been looking at is the angle of view. Although a spatial analysis would be fruitless in such a drawing, if we assume the broch is based on the 13m Mousa then the position of the horizon would put the 'camera' at around 15m height above ground. This is a low altitude aerial angle, only achievable in photography by kite, balloon etc.

In sorrel's work this is the rule and not the exception. Almost all of his reconstruction illustrations are made from low altitude aerial angles - high enough to lay out the site and expose the overall shape of it's components while low enough to retain a wide angle perspective and a sense of intimacy with the figures in the scene.

This parallel is encouraging for my own work and raises questions of how Sorrel derived these views, what reference he used and how much was down to imagination. These questions I intend to put to the Alan Sorrel Research Project, a collective who are studying his work and the memories of those who knew him.

Armit, I., Towers in the North, 2003, Gloucestershire: The History Press.

Saturday, 12 November 2011

Pole Aerial Photography at Ardestie Earth House

I chose this low lying site to try photographing with an eight meter pole, made with three window cleaning kits stacked together. In fact I started out with nine meters but quickly bent one of the sections by supporting it too low down. With more support a little higher up I was able to confidently position the camera above the site.

This Earth House is similar to the one which I photographed at nearby Tealing with the addition of three huts, the foundations of which remain in a row with one leading off into the curved cellar. A drain is also visible runing along the center of the earth house.

I hope that images captured in this way will be well suited for photogrammetry and will try processing this sequence at a later date. The advantages of PAP over KAP include an ease of use for capturing details, no reliance on wind conditions, and an alternative where kite flying may be impossible due to surrounding power lines, airports etc. For this reason it will be important to pursue as a backup if CAA permissions at Jarshof prove to be impossible.

Friday, 11 November 2011

The Dugout Canoe - Photogrammetry of a 1,500 Year Old Artifact

This ancient boat was lifted from the river Tay where it lay preserved for around 1,500 years. It is likely that dugout canoes such as this one where used to travel at least as far as between Dundee and the Loch Tay crannogs via the river Tay.

This example is on display in McManus Galleries where I photographed it from different angles and along it's full length. It's surroundings made it only possible to capture one side hence the dark holes which represent lack of data. I uploaded 100 photographs to Autodesk 123D Catch (formerly Autodesk Photofly) which returned a model of 16,000 vertices.

I have tried to light it in such a way as to bring out the relief detail of the wood as well as highlight the flat bottom of the vessel.

Wednesday, 2 November 2011

Terrain, Territory and Tentsmuir KAP

When thinking about how ancient sites would have looked from the air we can consider that the surrounding context may have been more unrecognizable than the site itself. Modern farming methods leave a graphic impression on the land, often a patchwork of straight and parallel lines which make it hard to visualize a site as it's first inhabitants may have found it.

It will be important in my reconstruction project not just to look at sources of untouched land but to think about the impressions which early settlers would have left on their surroundings. In communities who spent a lot of their time living and working outside we can assume that the unused land around ancient settlements would have been a web of paths, well worn by people and animals.

I took these kite photographs yesterday at Tentsmuir National Nature Reserve, a site largely undeveloped by human forces although it's many visitors have traced a network of paths in the dunes and flat land behind the beach. While exploring the landscape these visitors have caused a transformation reminiscent of what William Fox describes as "...converting land into landscape, or terrain into territory" (Fox, 2009). I found this a strong description of how our regard for a particular area can make a clear impression on the land as well as on the people who have interacted with it.

A fascinating aspect of Jarshof in Shetland is that people have been drawn to settle on the same site for over 4000 years. For whatever strategic advantage the location had it has been firmly claimed as territory time and time again. By reconstructing these changes using aerial perspectives I hope to enable the modern day visitor to build a familiarity of the site and ultimately their own claim to territory.

The dangers of using new media to present real history to an audience can be summed up by the arguments of the French theorist Jean Baudrillard. In fitting with the subject Baudrillard used the analogy of a map, or simulation, which is meant to represent a terrain, or reality (Baudrillard, 1994). The danger is that the "map" can become departed from the real, and while the audience accepts the simulation the reality can become obscured.

Interpretive reconstruction, while perhaps a contradiction of terms, is at the very least surrounded by issues of integrity. While it is tempting to use whatever imagery will instill a strong atmosphere in my film, it is a little pointless if not representational of the evidence and facts which have been established around the site.

While these photographs of Tentsmuir might provide a visually strong part of a backdrop to the bronze age settlement, it will be important to study the forces at work at the current day site as well as what can be interpolated about both geological terrain, and human territory, in the time of these ancient settlers.


Baudrillard, J., 1994, Simulacra and Simulation, Michigan: The University of Michigan Press.

Fox, W., 2009, Aereality, Berkley: Counterpoint.

The Crannog by Night

A very pleasant evening of storytelling and music at The Scottish Crannog Centre. I was interested to see how smoke from the fire seeped through the closed thatch roof. This is visible in the two 30 second exposures of the exterior.