Jarlshof December Site Visit

This photo taken by Kieran Duncan © 2011 shows me taking pole aerial photography sequences at Jarlshof near Sumburgh Head, Shetland. Although we were only on the island for three days the weather was kind and allowed for extensive photography to hopefully use for photogrammetry later. The close proximity of Sumburgh airport to Jarlshof restricts kite flying although my hope is that pole aerial photography will be suitable for capturing most of the site.



The winter conditions were visually pleasing in many ways with a dusting of snow bringing out the topography of the Norse part of the settlement (below, right). The benefits of an elevated view are immediately obvious at this site where features such as the curve of the broch wall (below, left), obscured by later structures and erosion, are difficult to make out on the ground.



A very satisfying first visit to the site which has left me with around 13,000 frames to work with towards digital reconstruction. Enough to keep me busy until my next visit!

Best wishes for the winter solstice and 2012!

Shell Photogrammetry Sub-Millimeter Test

This shell measures 27mm long and was processed into the 3D model below using macro photography and photogrammetry. This loop fades between true colour combined with artificial light, then grey topography and back again.



I was careful to light the surface in such a way that the shadow of the camera would be clear for all of the positions needed. The shell was supported with a pin and bluetac, visible at the base. This test was designed to explore the potential of these techniques for recording archaeological artifacts.

PAP and Photogrammetry Test at Ardestie

This test was derived from a series of pole aerial photographs. It shows the original colour projection, the topography under rendered lighting, and the two combined to artificially light the scene. Although not as polished as the Tealing test this was an experiment in the use of PAP for photogrammetry.

Jarlshof - Impressions of a 4000 Year History

I am working on this series of drawings and photo-montages in order to plan out angles of view as well as to study the colours and atmospheres which I will be looking to create in the digital reconstruction. These may also serve as a starting point for further archaeological consultation, I suspect that many of the details here will turn out to be woefully inaccurate.



Drawing is a good way to study the site and in this case I am increasingly aware of complexity of the chronology at Jarlshof, with buildings from different eras often built on top of one another.

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.

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.

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.