Alternative 3D Models: Multiple Vs Singular Interpretations

Wireframe

As part of my PhD project, over the last few months I have been researching trends in Visualisation from its incipit to today. I’m attempting to create a solid theoretical background upon which to build my own work, and in the process I am learning a lot of the philosophical and methodological foundations upon which 3D reconstruction stands.

There are many topics that I have found particularly interesting, some of which I have talked about before, and some of which I will write about in the near future. Today though I would like to concentrate on a topic I feel has only been discussed in passing: the creation of “alternative models”. Not only do I feel we need to dwell upon this subject more, I want to go against current trend to present a counterargument for their utility.

3D researchers have been advocating for alternative models from the start of Visualisation (Reilly 1992; Mathur 1997; Roberts and Ryan 1997; The Guardian 1999; Huggett and Guo-Yuan 2000). The basic idea is that it is impossible to present all hypotheses in a single 3D reconstruction, so a number of models should be reconstructed instead, each representing an alternative theory.

Alternative models fit within the general concept of accuracy. One of the major concerns with 3D reconstruction is the narrow scope for presentation of hypothetical data. Models are often built upon incomplete information, and as a result it is impossible to recreate a perfectly accurate representation of the past. There is a distinct worry amongst specialists and skeptics alike that without sufficient transparency 3D reconstructions may misinform and deceive an uninformed user (Bayliss 2003; Kensek et al. 2004; amongst many others). This concern is certainly founded, and while some suggestions have been put forward in an attempt to minimise the problem (Pang et al. 1997; Strothotte et al. 1999), the lack of a cohesive and enforced set of principles limits the reliability of 3D reconstruction as a methodology. We are moving in a positive direction, and publications such as the London Charter offer legitimisation of the use of these technologies (Beacham et al. 2006; Denard 2009). Yet there is still a need for enforced guidelines that can reduce, or at least explicitly state. inaccuracies.

The use of pink cement (Lock 2003), or Dell’Unto et al.’s (2013) levels of accuracy are good approaches to the problem, and the literature has embraced such ideas for the better. Alternative models, on the other hand, have been lurking in the background, often mentioned but never fully discussed. They are mostly used as an addendum or a failsafe, an attempt to silence any possible critic of the accuracy of the models. It is interesting how most of the publications that mention alternative models do not present alternative models themselves: papers concerned with the theoretical background use it as an example of ways to preserve accuracy, while technical papers omit alternative models altogether (with a few exceptions i.e. Roussou and Drettakis 2003). It is also important to note that they are always mentioned positively.

I would like to present a counterargument. I do not believe alternative models are bad, or that they have no uses. There are certainly occasions in which they can convey information more efficiently than other methods. I do however believe that they have a limited scope, and that using them as a way to present inaccuracies is counterproductive to the defining of a 3D methodology.

The limitations of alternative models can be expressed as so:

  • Physical and publication space managment
  • Time requirements
  • Multiple hypotheses representation

Physical and publication space management: using alternative models to present inaccuracies to the public or to fellow researchers requires for this information to be readily accessible. At present the issue with 3D documentation is one of space. Publications often do not possess enough space for a full documentation of the reconstruction process, and the problem is exacerbated in heritage management where information has to be tailored to an uninformed public. In most cases, the presentation needs cannot accommodate the presence of multiple models. Metadata and paradata are beginning to appear in publications through the use of online repositories, but the handling of multiple large models is still problematic.

Time requirements: 3D reconstruction is a process, which follows a number of steps. Work by Guidi et al. (2012; 2014) show an ideal example of the reconstruction procedure, with accumulative levels of detail and archaeological checks at the end of each phase. In order to reconstruct most alternative models, the split must occur right from the volumetric model. By doing so each variant must be constructed individually, or the subsequent changes must be reflected in each of the different models. Attempting to change the model in the later stages of production is still possible, but it requires more work, as there are more elements that need to be manipulated. Either way, the results is a distinct increase in the production time.

Multiple hypotheses representation: another logistical problem has to do with models with many conjectures. When is it necessary to create multiple models? If we are too strict with our definition of inaccuracies then every element in the reconstruction is in question. We would therefore end with numerous models with very subtle differences. On the other hand, if we we were too lax the purpose of using alternative models is void, as displaying only some of the hypotheses would render this process redundant. Additionally, if many hypotheses were to be displayed through alternative models, it would be necessary to create a model with every possible arrangement of hypotheses, exponentially increasing the number of reconstructions.

In addition to these limitations, my argument against the misuse of alternative models has to do with traditional methods of presenting archaeological data. Archaeological reports often attempt an objective analysis of the archaeological evidence, describing what has been found and trying to limit conjectures, frequently presenting multiple theories. Yet when interpreting an archaeological site, it is not uncommon to create a narrative. Certain evidence is omitted and new meaning is imposed on the remains, in an attempt to justify the current archaeological interpretation. Part of the scientific method is to present the data and propose a unifying theory, with the expectation that the theory shall change when new evidence comes to light. And archaeology subscribes to this view: while multiple scenarios may be presented in publication, there is often one preferred interpretation.

Therefore, in traditional archaeology the data is analysed to produce the results. Objective data is transformed into subjective interpretation, and with a change in the data comes a change in the interpretation. The uncertainty is accounted for in the source and not the output and the same should be true for 3D reconstruction. Metadata and paradata are paramount for the replicability of the process and for validating the hypotheses shown in the results. We must find better ways of preserving and presenting this form of information, to ensure the 3D methodology is valid. Alternative models however are part of the output, where subjectivity is allowed and even encouraged.

Critics often note that in Heritage Management the public is more susceptible to misinformation, making 3D reconstruction a ‘dangerous’ tool. Yet museum displays often present a single narrative, reducing complex archaeological issues to simplistic linear stories. While it is still a problem 3D reconstruction needs to address, the discussion has wider implications in the way we present data to the public.

Additionally, I am not saying that alternative models cannot have uses in archaeological presentation. In some cases the conflicting theories are at the core of the discussion, and alternative models help create a virtual representation of what this conflict appears like visually. A good example of this is the Patay-Horvath (2014) paper regarding the positioning of statues at the Temple of Zeus at Olympia. Here the alternative models are used effectively to communicate the main argument. It was however a deliberate choice from the author, and it had a specific purpose.

In conclusion, alternative models are not always the best option for presenting inaccuracies. While occasionally they can be effective in demonstrating conflicting hypotheses, in a wider methodology for 3D reconstruction they have little space. Presenting metadata and paradata still offers the best course for demonstrating uncertainty.

 

References:

Bayliss, R. (2003). Archaeological Survey and Visualisation: the View from Byzantium. Late Antique Archaeology Vol.1 No.1 pp.26-313.
Beacham, R. C., Denard, H. and Niccolucci, F. (2006). An Introduction to the London Charter. The E-volution of ICTechnology in Cultural Heritage.
Dell’Unto, N., Leander, A. M., Ferdani, D., Dellepiane, M., Callieri, M., Lindgren, S. (2013). Digital reconstruction and visualisation in archaeology: case-study drawn from the work of the Swedish Pompeii Project. Digital Heritage International Congress pp.621-628.
Denard, H. (2009). The London Charter: for the computer-based visualisation of cultural heritage.
Guidi, G., Russo, M., Angheleddu, D. and Zolese, P. (2012). A Virtual Connection between Past and Present: the Digital Revival of Cham’s Architecture (Vietnam). Virtual Systems and Multimedia pp.361-368.
Guidi, G., Russo, M. and Angheleddu, D. (2014). 3D survey and virtual reconstruction of archaeological sites. Digital Applications in Archaeology and Cultural Heritage 1 pp.55-69.
Huggett, J. and Guo-Yang, C. (2000). 3D Interpretative Modelling of Archaeological Sites/ A Computer Reconstruction of the Medieval Timber and Earthwork Castle. Internet Archaeology 8.
Kensek, K. M., Swartz Dodd, L. and Cipolla, N. (2004). Fantastic reconstructions or reconstructions of the fantastic? Tracking and presenting ambiguity, alternatives, and documentation in virtual worlds. Automation in Construction pp.175-186.
Lock, G. (2003). Using Computers in Archaeology: Towards virtual pasts. Routledge: London.
Mathur, S. (1997). Three Dimensional Representation of Archaeological Data in American Archaeology. Available at: https://web.archive.org/web/20000816044424/http://www.uiowa.edu/~anthro/plains/Termppr.htm. Last accessed: 31st Oct 2017.
Pang, A. T., Wittenbrink, C. M. and Lodha, S. K. (1997). Approaches to uncertainty visualisation. The Visual Computer pp.370-390.
Patay-Horvátz, A. (2014). The virtual 3D reconstruction of the east pediment of the temple of Zeus at Olympia – an old puzzle of classical archaeology in the light of recent technologies. Digital Applications in Archaeology and Cultural Heritage 1 pp.12-22.
Reilly, P. (1992). Three-dimensional modelling and primary archaeological data. In: Reilly, P. and Rahtz, S. Archaeology in the Information Age pp.92-107.
Roberts, J. C. and Ryan, N. (1997). Alternative Archaeological Representations within Virtual Worlds. In: Brown, R. 4th UK Virtual Reality Specialist Interest Group Conference – Brunel University pp.182-196.
Roussou, M. and Drettakis, G. (2003). Photorealism and Non-Photorealism in Virtual Heritage Representation. First Eurographics Workshop on Graphics and Cultural Heritage.
Strothotte, T., Masuch, M. and Isenberg, T. (1999). Visualizing Knowledge about Virtual Reconstructions of Ancient Architecture. Computer Graphics International.
The Guardian (1999). Megabytes of megaliths. 23rd September 1999.
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How Video Games help present and interpret Neolithic Malta.

 

Hi all,

I gave a talk yesterday as part of Queen’s University Belfast PGR Talks. I had it recorded as I thought it would be interesting to share here some of my recent results.

I intended this presentation for those who may not be familiar with the topic, so it may be a bit vague at times, but it should provide a useful introduction to 3D reconstruction and gaming software.

Please feel free to share your thoughts and questions in the comment section.

Rob

Interpreting and Presenting Archaeological Sites Using 3D Reconstruction: Virtual Exploration of the Xaghra Brochtorff Circle in Gozo.

Unity 1.jpeg

Hi all,

Just as a heads up, I have uploaded my MPhil dissertation to Academia.edu, so go and check it out.

It’s available here.

It discusses 3D reconstruction in the Maltese islands, as well as using gaming software to analyse archaeological sites.

Feel free to comment here with any questions you may have. I’m hoping to increase communication on this platform this year!

 

Rob

A Unity 3D script for displaying uncertainty in 3D Reconstructions.

Following up from my latest post, I wanted to share with you one of the solutions I used as part of my MPhil project.

As discussed, a real problem with 3D Reconstruction in archaeology is the subjectivity of the modelling process. While Photogrammetry and Laser Scanning record archaeological features as they are, reconstructions rely on information that is more or less inaccurate. Strothotte et al. (1999) pointed out that uncertainty in Visualisation is caused by imprecision and incompleteness. Site reports tend to present a limited range of data, usually in a 2D format that may not translate to 3D which causes imprecision (Worthing and Counsell 1999). And while interpretation of a site can be built on incomplete information, 3D Reconstruction requires answers to very specific questions that rarely can be answered by the archaeological evidence.

In a bid to display this uncertainty, projects have displayed the model entirely using wireframes or point clouds (Richards 1998). I propose a similar solution: by using a Unity 3D script heavily based on work by Naojitaniguchi (2015), we have different toggles to switch between fully rendered, wireframe and removed. The most uncertain elements are tagged for removal, leaving the more accurate features intact.

Within the scene, the wireframe looks like so:

wireframe

Wireframe 2Wireframe

The Player script initiates the script by attaching it to the objects targeted for removal upon the input of a button:

void RemoveArchaeology(){
		if (Input.GetAxisRaw ("Remove") != 0 && archaeologyRemoved == 0 &&
			removeAxisInUse == false) {
			archaeologyRemoved = 1;
			removeAxisInUse = true;

			foreach (GameObject go in gameObjectArray) {

				go.gameObject.AddComponent ();
			}
		} else if (Input.GetAxisRaw ("Remove") != 0 && archaeologyRemoved == 1 &&
			removeAxisInUse == false) {
			archaeologyRemoved = 2;
			removeAxisInUse = true;

			foreach (GameObject go in gameObjectArray) {

				VertexRenderer vertexRenderer = go.GetComponent ();
				vertexRenderer.RevertToStart ();
				Destroy (vertexRenderer);
				go.SetActive (false);
			}
		}	else if (Input.GetAxisRaw ("Remove") != 0 && archaeologyRemoved == 2 &&
			removeAxisInUse == false){
			archaeologyRemoved = 0;
			removeAxisInUse = true;

			foreach (GameObject go in gameObjectArray) {
				go.SetActive (true);
			}
		}

		if (Input.GetAxisRaw ("Remove") == 0){
			removeAxisInUse = false;
		}
	}

Then, the VertexRenderer script replaces the model with lines:

using UnityEngine;
using System.Collections;

		//Code written by R. P. Barratt
		//robbarratt1@outlook.com
		//
		//Heavily based on a script by Naojitaniguchi (2015).

		//Renders the selected elements as lines.

public class VertexRenderer : MonoBehaviour {

	public Color lineColor;
	public Color backgroundColor;

	private Vector3[] lines;
	private ArrayList linesArray;
	private Material lineMaterial;
	private MeshRenderer meshRenderer;
	private Material initialMaterial;

	public void Start () {

		//Finds the components.
		GetComponent<Renderer> ().enabled = false;
		meshRenderer = GetComponent<MeshRenderer> ();
		if (!meshRenderer) {
			meshRenderer = gameObject.AddComponent<MeshRenderer> ();
		}

		//Saves the initial material.
		SaveInfo ();

		//Finds the line material and sets it.
		Shader shader1 = Shader.Find ("Lines/Background");
		meshRenderer.material = new Material (shader1);
		Shader shader2 = Shader.Find ("Lines/Colored Blended");
		lineMaterial = new Material (shader2);
		lineMaterial.hideFlags = HideFlags.HideAndDontSave;
		lineMaterial.shader.hideFlags = HideFlags.HideAndDontSave; 

		//Creates a list of lines based on the mesh.
		linesArray = new ArrayList ();
		MeshFilter filter = GetComponent<MeshFilter> ();
		Mesh mesh = filter.sharedMesh;
		Vector3[] vertices = mesh.vertices;
		int[] triangles = mesh.triangles; 

		for (int i = 0; i < triangles.Length / 3; i++) {
			linesArray.Add (vertices [triangles [i * 3]]);
			linesArray.Add (vertices [triangles [i * 3 + 1]]);
			linesArray.Add (vertices [triangles [i * 3 + 2]]);
		} 

		lines = new Vector3[triangles.Length];
		for (int i = 0; i < triangles.Length; i++) {
			lines [i] = (Vector3)linesArray [i];
		}

		//Sets material.
		meshRenderer.sharedMaterial.color = backgroundColor;
		lineMaterial.SetPass (0);
	}

	public void OnRenderObject(){

		//Draws lines based on mesh.
		GL.PushMatrix ();
		GL.MultMatrix (transform.localToWorldMatrix);
		GL.Begin (GL.LINES);
		GL.Color (lineColor); 

		for (int i = 0; i < lines.Length / 3; i++) {
			GL.Vertex (lines [i * 3]);
			GL.Vertex (lines [i * 3 + 1]); 

			GL.Vertex (lines [i * 3 + 1]);
			GL.Vertex (lines [i * 3 + 2]); 

			GL.Vertex (lines [i * 3 + 2]);
			GL.Vertex (lines [i * 3]);
		} 

		GL.End ();
		GL.PopMatrix ();
	}

	void SaveInfo(){

		//Saves initial material.
		initialMaterial = meshRenderer.material;
	}

	public void RevertToStart(){

		//Returns to initial material.
		GetComponent<Renderer> ().enabled = true;
		meshRenderer.material = initialMaterial;
	}
}

The script requires Unity3D to run at the moment, but I am sure it can be adapted for other platforms.

The reason for this script is to allow users to choose different options, displaying the finished model with a more realistic skin but also allowing for a more accurate representation.

References:

Naojitaniguchi (2015). WireFrame. Available: https://gist.github.com/naojitaniguchi/862724c55bd322695511. Last accessed 20th Oct 2017.

Richards, J. D. (1998). Recent Trends in Computer Applications in Archaeology. Journal of Archaeological Research Vol.6 No.4 pp.331-382.

Strothotte, T., Masuch, M. and Isenberg, T. (1999). Visualizing Knowledge about Virtual Reconstructions of Ancient Architecture. Computer Graphics International.

Worthing, D. and Counsell, J. (1999). Issues arising from computer-based recording of heritage sites. Structural Survey Vol.17 No.4 pp.200-210.