Can't believe it's nearly the end of October, it doesn't seem two minutes since we were on site at Swandro, and here we are busy planning for our 2023 season. Today we have a special treat for you, with a piece by our very own Bonnie Burton. Bonnie has been with the project since her undergraduate days and is now busy working on her PhD: Investigating the loss of archaeological heritage to coastal erosion through multi-disciplinary 3D digital documentation and developing a digital recording framework for fragile coastal archaeology.
She has very kindly put together the piece below, explaining her research and its significance - enjoy!
An introduction to 3D Digital Documentation By Bonnie (Nicole Burton)
Introduction
3D digital techniques are a well-known toolkit for researchers across the globe. The instruments can record a given surface or object, ultimately capturing a moment in time. The research utilises; terrestrial laser scanning (TLS), Structure-from-motion photogrammetry (SfM) and Unmanned Aerial systems (UAS). The significance of these techniques lies within the ability to obtain a 3D record of a given subject area, the ability to investigate impacts of erosion and aid in further interpretations of the site.
Significance
As these techniques provide a ‘snapshot in time’ it becomes a meaningful methodology for coastal monitoring. For example, the Knowe of Swandro, a Scheduled Ancient Monument (Historic Environment Scotland) has already undergone extreme coastal erosion and is under threat of further loss. 3D data allows for comparing multiple datasets to understand the impact of coastal erosion as well as aiding in management strategies. For example, the Knowe of Swandro has been 3D digitally documented since 2015, allowing modern 3D data to be overlayed and compared to one another. This can aid in identifying the loss of archaeological material and sediments.
Digital Techniques
Each 3D digital technique comprises of advantages and disadvantages, particularly focusing on cost, time and resources. In the case of Swandro, due to the complex nature and vulnerability of the site, as well as available resources, all techniques have been applied to 3D record the site. However, not all vulnerable sites are fortunate to be in the same situation. This means flexibility needs to be considered when choosing the appropriate technique.
A terrestrial laser scanner is a portable instrument which works in a line-of-sight motion, this means multiple scan locations are needed to create a 3D model. The scanner is mounted onto a tripod and then levelled, using the onboard scanner's spirit level bubble. This task can be difficult on uneven terrain, which is extremely challenging on Swandro’s boulder beach. The instrument works by emitting a laser beam to a surface and this beam is then bounced back, collecting billions and billions of points for accurate geometric data. The instrument also takes a series of photographs for colour value.
Structure-from-motion photogrammetry is carried out by using an off-the-shelf camera, which relies on a series of overlapping photographs of a given object or surface. Prior to data capture, a colour corrector should be used, along with the selection of appropriate camera settings (i.e brightness, aperture, shutter speed etc.) which is variable depending on the environmental conditions. Photographs are taken of all angles of a given surface or site, ensuring there are no holes in the 3D model. When we refer to holes, we mean, areas that have not been documented. Once photographs are captured, the data was processed. Here, 3D models are generated, producing high-quality textural 3D models, which allows us to investigate the impacts of coastal erosion (i.e. wearing and cracking of stonework).
An Unmanned Aerial System (UAS) should be carried out by an individual with a drone license, along with appropriate documentation. The methodology of this technique works by either manually or automatically traversing the UAS above the site and taking overlapping photographs for the 3D model. The UAS must be deployed in good weather conditions, as it has the potential to capture low-quality data, and damage could be made to the drone or the monument. The processing of the data is carried out in a similar way to Structure-from-motion photogrammetry.
Once all data has been processed, they can be brought together using multiple software packages, to create one singular 3D model. Here, the 3D model will be a highly accurate 3D geometric model with high-quality textural data. In addition, all models should be correctly georeferenced, this will allow for accurate comparison between multiple datasets, to fully comprehend erosion.
Conclusion
In conclusion, this short piece has introduced key 3D digital documentation techniques that aid in monitoring and 3D recording vulnerable cultural heritage sites, as well as their strengths and weaknesses. It has also discussed the importance of applying such techniques, and the flexibility the user needs to have when considering which technique to use.
So there you have it, thank you again to Bonnie for her piece, and we all look forward to reading her PhD (and also the chapter we'll doubtless get her to write in the final Swandro monograph).