PART 1 – Visualisation

ggantija

“Visualisation” is a term that is used quite consistently in recent archaeological publications. It refers to the reconstruction of archaeological evidence through the use of computer software, although it originates in the practise of recording the site using 2D drawings which has been around for a few centuries. Although the meaning of the word and what it entails fluctuates somewhat, I’ve come to identify three types of technologies that fall within this category:

  • Photogrammetry
  • Laser Scanning
  • 3D Reconstruction

Photogrammetry is also referred to as Structure From Motion, and differs from the other methods as the 3D models are based on photographs (Pedersini et al. 2000). Similarly to laser scanning, the result is a high density point cloud, with photorealistic textures.

Laser scanning is a powerful tool widely used in large scale recording. It uses laser measurements to calculate the position of points in a site, and like Photogrammetry it produces a textured mesh, although generally laser scanning models are much more dense and therefore more accurate.

3D reconstruction is the method we will be primarily dealing with. It is less accurate than Photogrammetry and laser scanning, and the results are less realistic. It does however possess some distinct advantages. Reconstructed models are easily manipulated, and often represent elements of a site that have been lost (Fig.1). They can also be combined with gaming software to create interactive environments (I could cite many authors here, but just as a taster I would recommend reading Champion et al. 2012).

image 1

Fig.1 = 3D Reconstruction of the site of Ggantija, Gozo.

The three methods have very different aims, and as such it is important to know what you want to achieve before applying them:

  • For small and medium scale recording Photogrammetry is excellent (Scopigno 2012). It is very cheap and fast, and possesses the accuracy and visual effects that are necessary for recording and presenting. It is ideal for cataloguing finds or small scale excavations, although it can be used for larger features if necessary (see the current Must Farm excavation models by Donald Horne for more details: https://sketchfab.com/mustfarm). The fact it possesses lower points than laser scanning makes it easy to manage, and it requires little training.
  • For detailed models and large sites Laser Scanning is the tool of choice. More expensive and computationally challenging than Photogrammetry, laser scanning creates precise models that are perfect for recording, presenting and some interpreting. A great example is the work of John Meneele (https://www.facebook.com/1manscan/) who has been analysing stone decay be comparing models taken in different years. I personally have little experience with laser scanning, but the results I have seen have shown a lot of promise.
  • 3D Reconstruction is mainly for presentation and interpretation. Although some arguments have been put forward on using 3D reconstructions for metadata recording, this is not where the technology shines (Reilly 1990; Barreau et al. 2013). 3D reconstructions can show a site “as it was” rather than “as it is”, leading to a more vivid understanding of archaeological contexts (Miller and Richards 1995; Lewin and Gross 1996). For the general public it is perfect, and it can be made highly interactive in order to further increase user comprehension of the archaeology. As for interpretation, the use of scripting allows a number of tools to be created in order to answer archaeological questions. One of the projects I have been working on was looking at analysing solar alignment at a Maltese site, and through a custom-written script I concluded the site is illuminated on the winter solstice (Fig.2). While Photogrammetry and Laser scanning shine with precision and photorealism, 3D Reconstruction truly dominates in presentation and interpretation.

 

overall image

Fig.2 – Overview of the script interface.

It is important however to mention how these methodologies are not mutually exclusive. Little work has been done in combining different techniques, but the results show much promise. A previous article on this blog discussed virtual museums, and the combination of a 3D reconstructed environment, with Photogrammetric models within.

In conclusion, there is a lot of technology put there, and although research is slowly unveiling the advantages of each there is much to be discovered still. With 3D Reconstruction we are barely scratching the surface, and only in the last 10 years we have had custom written scripts for archaeology. It may take a while, but once we uncover what is possible, archaeology will really reap the results.

 

In the next post I will be looking at previous work in 3D reconstruction, with a few examples of significant projects that have helped shape the methodology.

 

REFERENCES:

Barreau, J., Gaugne, R., Bernard, Y., Le Cloiree, G. and Gouranton, V. (2013). The West Digital Conservatory of Archaeological Heritage Project. Digital Heritage International Congress. Vol.1 pp.547-554.

Champion, E., Bishop, I. and Dave, B. (2012). The Palenque project: evaluating interaction in an online virtual archaeology site. Virtual Reality 16 pp.121-139.

Lewin, J. S. and Gross, M. D. (1996). Resolving Archaeological Site Data With 3D Computer Modeling: The Case of Ceren. Acadia pp. 255-266.

Miller, P. and Richards, J. (1995). The Good, the Bad, and the Downright Misleading: Archaeological Adoption of Computer Visualisation. In: Huggett, J. and Ryan, N. Computer Applications and Quantitative Methods in Archaeology. Oxford: Tempus Reparatum pp.19-22.

Pedersini, F., Sarti, A. and Tubaro, S. (2000). Automatic monitoring and 3d reconstruction applied to cultural heritage. Journal of Cultural Heritage 1 pp.301-313.

Reilly, P. (1990). Towards a virtual archaeology. In: Lockyear, K. and Rahtz, S. Computer Applications in Archaeology pp.133-139.

Scopigno, R. (2012). Sampled 3D models for Cultural Heritage: which uses beyond visualisation? Virtual Archaeology Review Vol.3 No.5 pp.109-115.