Virtual Museums. When Heritage does not exist

J. A. Barceló

Is there anything in Virtual Archaeology but wonderful images? General audiences like virtual reconstructions, and may be there are opportunities for archaeologists and computer scientists to "sell" the Past dressed in beautiful colours, textures and shapes. But are we doing history (or anthropology, or sociology,...) when we reconstruct archaeological sites using VR techniques? This paper is a general introduction to VR techniques. They should not be presented as a way of doing reconstructions, but as a simulation of archaeological reasoning. If "Interactivity" is the key word in Virtual Reality, then we should understand it not as a way of "moving" through a computer representation, but as a "manipulation" of an archaeological interpretation.

In March 1998, during the Computer Applications in Archaeology International Conference, a special session on Virtual Reality in Archaeology, open to all audiences, was scheduled. Most media published announcements, and as a result, 1000 people assisted. At the same time, traditional museums of archaeology are empty. "Virtual" archaeological worlds seem to be "popular". The introduction of greater realism into the look of computerized reconstructions makes the models more attractive and interesting to a larger audience (Reilly 1990). Publications (Forte 1996) and multimedia material (see, for instance, the Virtual Pompeii CD Rom, http://cdaccess.com/html/pc/pompeii.htm) are also examples of the popularity.

If we consider the term Virtual-Reality as a generic 'blanket' descriptor to refer to the growing range of dynamic-interactive visualisation (Gillings 1999, Lloret 1999), then audiences seem to be looking for new ways of "looking" at the past. Archaeological virtual models become clues for interacting with the past, that is, for bringing the past to the present. Consequently, the primary aim in using VR in archaeology should be to provide a basis upon which the viewer can and will project and visualise a reality (Goodrick 1999).

"Interactivity" between the "user" and the historical (archaeological) knowledge is allowing the creation of the first "Virtual Museums" (Shaw 1994, Loeffler 1994a, Gottarelli 1996, Gordon 1999, Refsland 1998, MOSAIC, Infobyte: (http://www.infobyte.it).

What is a virtual Museum? It is a virtual theatre where it will be possible to dive into a number of cultural visits through ancient monuments. It will then be possible to "stage" virtual exhibitions, uniting and comparing works of art which could difficulty be moved from their place of conservation. The visitors will be able to go back in time and see ancient sites as well as monuments in their reconstruction in different eras. The entire range of multimedia technologies with areas for consultation of art CD-ROMs and places for interactive Internet navigation will also be available to the public.

Let us consider some examples. The St. Peter's Basilicas Virtual Reality project is advertised as a unique experience: travelling back in time. The virtual visitor not only has the possibility of freely exploring the reconstruction of the interior of the current Basilica, but more as well. The virtual visitor may exit the Basilica and walk outside within the area enclosed by Bernini's colonnade. At this stage, by pressing a button, the time trip begins making it possible for the user to visit the Constantinian Basilica with its external cloister both of which demolished in the 16^th century to make room for St. Peter's as we know it today (http://www.infobyte.it). Another example is the Virtual Stonehenge Project (Burton et al. 1999). Upon entering the model the screen splits into two, text on the left and the 3D world on the right. Here there is a two-way link in operation so that highlighting given words or phases reveals the related object, and highlighting an object invokes a text description. As well as this textual-graphical interaction, and the ability to manoeuvre freely about the landscape, there are other options. For example, a visitor can take a guided tour or stand within the stones and watch the sun rise along the Avenue. But perhaps the most exciting feature is the ability to explore the landscape within a series of time slices spanning 10500 years. The inclusion of this further dimension creates an even more dynamic model, allowing any user the ability to quickly build up a picture of the current opinions on the evolution of the Stonehenge landscape.

Stonehenge remains are easily accesible by visitors, but roman Wroxeter is still buried under pasture land, and thus invisible to the visitor. The British Telecom Access to Archaeology project aims to make the non-structural data available, in a coherent way, to as a wide range of interested parties as possible. The primary output is a software product that can be accessed over the internet and via CD, to educational organizations. It is using two main approaches to present this data. These are a virtual reality reconstruction of the city and an interactive, digital landscape, representing the Wroxeter Hinterland. The project is designed to allow users not only to explore the data, in ways that will give them insights into archaeological interpretations, but also to understand how data, leading to these conclusions, has been collected and analysed (Exon and Gaffney 1999)

The VisTA system is one of the most advanced Virtual Museum models available. It was originally designed as an interactive simulation system for the development of research into ancient villages. It was then extended as a bridge between experts and non-experts in the sense that both could use it for different purposes.The users of VisTA can walk-through reconstructed villages to see their landscapes and get information on each house as well as see the development of a village over time. Initiating the VisTA system, a user first chooses one database of an excavated site. This database includes 3D terrain data of the site and data on the positions, sizes, and types of buildings. To indicate the positions of buildings, the system displays floor marks which correspond to the floor shapes of the buildings. The user picks floor marks one by one and for each, inputs the building type, terms of existence, and identification name. By doing this process on all or some of the floor marks in the village, the user can simulate the transition of the village over time and check his/her hypotheses through 3D computer graphics. Users can also "walk around" a reconstructed village and see the structures in a house while simulating the development of the village in a particular year. This allows the users to investigate the view from any point in the village (Kadobayashi et al. 1999)

Virtual worlds can be much more than sets of fancy pictures; objects throughout the World can be linked to text, image, and sound databases permitting self-guided educational or research virtual tours of ancient sites in which users can learn about history, construction details, or daily life with a click of the mouse. Worlds programmed in VRML can be sent over the Internet or run off CDs providing an interactive and exciting research experience. Alternative publications can supplement or complete traditional paper-based source material; for instance, a 3D computer model can be a visual index to an excavation report. The same models and virtual worlds can also be used for up-to-date instructional materials for public schools or museums directly engaging students or the general public in a participatory learning experience using the very latest archaeological evidence. We can create a globally integrated and interactive system of linked virtual worlds for teaching, research, archaeological fieldwork, museum exhibitions, and on-site interpretation centers. Using virtual reality as the container to which all other data and image types are linked offers unprecedented access to information. Whether computers help to change the questions we ask of the past may depend on the techniques chosen to visualize the answers (Sanders 1999).

From the point of view of archaeologists, the aim of those "virtual projects" seems to be to demonstrate that archaeologists can produce realistic records of the data they inevitable destroy in the course of excavation. By constructing detailed models of the excavated material, archaeologists can re-excavate the site and search for evidence which escaped attention during the actual dig (Reilly 1990). Some visualizations are intended for use in exploration and analysis in which the user has some ideas about what they are looking for, but is not fully sure. On the other hand, visualizations are often prepared for presentations intended to communicate one's findings to others. The key difference here is between the need to understand the data better, versus the user's desire to communicate some particular understanding that has already been reached.

There is the issue of how best to inform the viewer on the degree of confidence that can be investigated in each element of the reconstruction. We should remember that transforming an entity (object or concept) from a non-visual to a visual representational domain is an analogical task, and consequently there is not any identity between the entity and its "visualization" (Goldstein 1996). There is much criticism about the gap still remaining between the interpretation and the original data. It is not readily apparent how one gets from the dig to the interpretation (Reilly 1990, 1992, Goodchild et al. 1994)). As with reconstructions, however, the observer might not be fully aware of how much of a particular picture was conjectural, since the whole image seems "perfect".

To date, the catalyst for visualization in archaeology has not been the search for improved techniques for discovering new knowledge but rather for improved ways for presenting existing knowledge to the public (Miller and Richards 1995). Given that 'image' is a way of making sense of information, we need to know the purpose of the image, but most "virtual projects" have no purpose. In most cases the use of virtual reality in archaeology seems more an artistic task than an inferential process. Virtual Reality is the modern version of the artist that gave a "possible" reconstruction using water-colours. Computer scientists take the drawings of this "imaginative" reconstructions, and transform them into computer language. The Computer gives 3D, colour and texture to archaeologists (or architects) imagination.

As a direct result of the uncritical acceptance of virtual archaeological models, fundamental questions relating to issues such as what we actually mean by Virtual-Reality, and what our expensively assembled models truly represent have been left largely unexplored. Simply put, the better and more optimised the data used in its construction, the more faithful the Virtual model is, and the closer it comes to the reality it seeks, or purports, to represent. In addition, as a result of this notion of the Virtual-Reality model as a painstakingly sophisticated surrogate, the reconstructions run the risk of being reified, becoming in effect end-products, finished, completed, free-standing and there to be visually devoured. The point here is that any given Virtual-representation can never be authentic. The considerable efforts currently being expanded in incorporating ever more detail into models, whether through the use of individual bricks and stones rather than simplified macro-entities, or the application of highly complex textures, achieve little more than the generation of an even more fastidious investigative attitude on the part of the observer (Miller and Richards 1994, Gillings 1999).

The advantage of virtual computer models in respect of traditional analysis is evident. Any computer generated virtual model (visualization) must be regarded as a spatial reconstruction of a fragmented physical source, thus based on world coordinates, sufficient to generate the completed archaeological artefact as a measurable duplicate. The computer modelled solid must be regarded as a measurable solid space, which only has existence within the computer. Therefore, the creation and visualization of archaeological 3D models should be considered as a laboratory which allows, the objective testing of data acquired in the field and its interpretation. Quasi 3-D approaches used in GIS, in which the third dimension is treated as a variable, should not be confused with true 3-D systems in which multiple attribute data may be recorded for any unique combination of three-dimensional space represented along independent axes. Three-dimensional topology would permit spatial queries such as "what is next to", what surrounds, what is above, below, to the side of, etc. (Harris and Lock 1996), or the provision of complete physical properties (mass, volume, centre of gravity, moments of inertia, radii of gyration etc.), as well as the ability to generate section views, add full visual physical properties, and detect interference between adjacent components (Daniel 1997).

The concept virtual archaeology was first proposed by Paul Reilly (1990). The key concept is virtual, an allusion to a model, a replica, the notion that something can act as a surrogate or replacement for an original. In other words, it refers to a description of an archaeological formation or to a simulated archaeological formation. As a tool for scientific analysis, the visualizing process resulting from solid modeling can sometimes reveal relationships within an archaeological 'reconstruction' more clearly than any other current methods of display (Fletcher and Spicer 1992, Molyneaux 1992, Miller and Richards 1994). A virtual model is a form of representation. It can be used for communicating with others, as an aid to memory, but specially it may allow us to formulate inscriptions which we can work with and manipulate so as to expand our knowledge. We do not just look at the world, or into an internal store of ideas, and "know things": we calculate, manipulate, and "work things out" in response to our needs. We perform tasks, we solve problems, we work out answers to questions posed by others, and our effectiveness in doing these things depends in part on the Form of Representation we use (Peterson 1996). Because a structural (geometric) model is attempting to represent a real structure rather than merely its appearance, it should be possible to interrogate the model as to some or all of its physical qualities, and this is possible only with solid models. Armed with information about the material from which an entity or group of entities are constructed, solid modellers are able to calculate such things as the volume, mass (using finite element analysis), centre of gravity, moments of inertia, radii of gyration and stresses. The model is thus able to provide us with information which previously was only possible with laborious calculation, such as questions about the strength of the building, and the quantities of materials needed to build it. I can find no evidence that much, if any, work of this nature has been carried out in buildings archaeology. (Fishwick 1995, Daniel 1997).

Archaeological visualization is then a way of modeling past information, and not a photograph of ancient data (Daniel 1997). Suppose we have archaeological data, collected at a set of scattered locations. In almost all cases, these data can be regarded as samples of some underlying entity (an object, an activity area, a building, a territory, a landscape, etc.) and, indeed, it is this underlying entity which we wish to display, not the data. To "visualize" the archaeological record means then, the building of a geometric model of that underlying entity. Input data are spatial variables describing the entity, that is any quantitative or qualitative property of archaeological data varying spatially (topologically or according to a specific distance measure), and which contribute to explain the dependency relationships between the locations of the object, activity area, building, territory, or landscape we wish to study . If a point is the model of an archaeological entity location, by joining points with lines, fitting surfaces to lines, and "solidifying" connected surfaces, we should try to explain the shape and morphology of the archaeological entity . That is to say, any "visual model" is in some way a spatial model that reflects a decomposition of space in "units" (points, lines, areas, etc.) with the idea that if we can specify the (spatial) behavior of each unit, we can understand the behavior of the whole system (Fishwick 1995).

Nevertheless, the archaeological record is not a set of points, lines, surfaces, sections or blocks. Neither is it a continuum except in the broadest sense of the term. Every archaeological unit (a vase, a bone, a house, a territory) can be described as an irregular or regular volume with distinguishing characteristics. The boundaries between units create discontinuities that are further complicated by intrinsic archaeological factors (deposition and post-deposition, for example). Within this heterogeneous complexity we are concerned with variables, such as artifact concentrations (activity areas), presence/absence of some archaeological properties or any other feature that is continuously variable within the volume of a unit, but discontinuous across boundaries. To adequately represent this complex environment on a computer we must consider a semi-infinite continuum made up of discrete, irregular, discontinuous volumes which in turn control the spatial variation of variables. The possibilities of using geometric elements to visualize archaeological numerical data do not signify that data in real life correspond directly to abstract geometric elements. We should not create wonderful imaginative illustrations of the past, but using geometry to explain some properties of the data set, that is, properties related with shape, size, time and location.

To generate numerical archaeological data to be visualized, we need to identify the independent spatial variables and the dependent ones. In archaeology, like in other disciplines, dependent data are related to the properties of archaeological entities, and the independent variable refer to position and location. We have the following possibilities:

1. Two-dimensional Modelling

T time location (independent variable)

W₁ ,... W_n presence/absence/quantity of any archaeological entity (artefact, structure, ecological data, soil type, etc.)

2. Three-Dimensional Modelling

X,Y 2D point coordinates: longitude, latitude (independent variables)

Z heigth or stratigraphic depth (dependent variables)

3. Four-Dimensional Modelling

X,Y,Z 3D point coordinates: longitude, latitude, heigth/depth (independent variables)

W₁ ,... W_n presence/absence/quantity of any archaeological entity (artefact, structure, ecological data, soil type, etc.)

4. Mixed Models

X,Y,Z, T 4D point coordinates, longitude, latitude, heigth/depth, time (independent variables)

W₁ ,... W_n presence/absence/quantity of any archaeological entity (artefact, structure, ecological data, soil type, etc.)

1. Two-dimensional Modelling. In the first case, we are involved with two-dimensional data sets which contain only a single value at every point . This is the classical example of archaeological simulation, where a single line or curve explains the relationship between time (as represented by stratigraphic ordering of some archaeological complex) and any other quantitative variable (the quantity of rubbish accumulation pottery sherds, for example).

2. Three Dimensional Modelling. Here, we deal with the problem of shape.Archaeological numeric data are refered to a surface measured at some points whose coordinates are known. By tracing lines, curves and surfaces between coordinates, we create a geometric model of shape. Here the concept of shape is defined as the total of all information that is invariant under translations, rotations and isotropic rescalings (Small 1996), that is, those aspects of the data that remain after location and scale (size) information are discounted. It is then a quantitative property about spatial location and size. Everything that has size and location, has shape. Given this definition, we can create geometric models of any archaeological entity: a stone, vase, pit, house or territory. Shape is a field for physical exploration, because it has not only aesthetic qualities, nor is shape just a pattern of recognition. Shape is determining also the spatial and thus the material and the physical qualities of objects and buildings (Sheppard 1989, Steckner 1996, Lukesh 1996).

The most characteristic three-dimensional models are those of physical archaeological entities, like objects and buildings.

But not only those typical elements have shape. Topographic coordinates have been used to build a geometric model of the topography of the area where the archaeological site once existed (Zack 1999, Berry et al., 1998).

Those models are not "photographies" of archaeological data, but visual models of the geometry of three dimensional data (Sheppard 1989). Those data are the three-dimensional coordinates of the vase profile, the three-dimensional coordinates of different architectonic elements: walls, columns, archs, windows, ceiling, etc., and the three-dimensional coordinates of topography. Because they are not single pictures, geometric properties (curvature, length, thickness, heigth, volume, etc.) can now be measured on these models.

In other words, any 3-D data set may have shape. It is common that some statistical results are being presented using 3D visualization techniques (Wunsch 1999, Beardah and Baxter 1999). In fact, this graphic representation offers only a false three-dimensional visualization. The representation is based on a two-dimensional distribution of the data, and provides, in a three-dimensional form, a view of the density of points.

3. Four Dimensional Modelling. Here we introduce the time dimension. We are trying to "see" how time is involved in the changing pattern of shape modification, that is by changes in the state of an entity. Computationally, this can be simulated using animation techniques (Castleford 1991, MacEachren 1994, Johnson 1999, Daly and Lock 1999).

4. Mixed Models. We can add some more dimensions to any geometric model. The most typical example is that of a 3D map, showing a visual representation of the relationship between soil type, hydrography (dependent variables) and topographic position (independent variables).

The more independent variables the system has, the more complete the resulting model is. We are not limited to 4 variables (x, y ,z, w ), but we can in fact relate two or more three dimensional models (x₁, y₁ ,z ₁, w₁ ), (x₂, y₂ ,z₂, w₂ ). For instance, we can analyze the dynamics of the interaction between site form ( a three dimensional shape model) and topography (another three dimensional shape model). The 2 dimensional traditional maps do not reveal details of slope and aspect. Although the location of the archaeological features is noted, one cannot easily determine the relationship between these features and the terrain. There are obvious differences between terraces on the slopes of a hill and terraces which are merely slightly flatter areas of an already flat landform. These differences are more easily quantified and assessed from a 3 dimensional model (see Lukesh 1996, Reeler 1999, Messika 1999, Leusen 1999).

From Virtual Models to Enhanced Reality

Simulation embodies the principle of "learning by doing" - to learn about the past we must first build a model of the past and make it run. To understand reality and all of its complexity, we must build artificial objects and dynamically act roles with them.

Just as the desktop metaphor allows users to interact easily with computer's file structure, useful interaction metaphors are needed for virtual environment systems. Key element of a virtual environment is the ability to move in three dimensions, and it should help us to bridge the gap between the "outside" material world and the conceptual worlds we carry around the "inside", in our heads and bodies.

This property has lead to the concept of "enhanced" or "augmented" reality (AR). Augmented reality has been defined as the simultaneous acquisition of supplemental virtual data about the real world while navigating around a physical reality. It is different to the concept of "immersive reality", where the eyes and ears or other body senses are isolated from the real environment and fed only information from the computer, providing a first-person interaction with the computer-generated world. For information pertaining to complicated 3D objects, augmented reality is an effective means for utilizing and exploiting the potential of computer based information and databases. In augmented reality the computer provides additional information that enhances or augments the real wold, rather than replacing it with a completely virtual environment. In AR the computer contains models of significant aspects of the user's environment. AR provides a natural interface for processing data requests about the environment and presenting the results of requests. With 3D tracking devices a user may conduct normal tasks in his/her environment and the computer is capable of acquiring and interpreting his/her movements, actions and gestures. The user can then interact with objects in the real world, generate queries, and the computer provides information and assistance. Merging graphical representations of augmenting information with the view of the real object clearly presents the relationship between the data and the object. Using AR, the user can easily perceive and comprehend the spatial component of the queried data (Rose et al. 1995).

A good example of augmented reality is The Longmarket Roman building Model at Canterbury (Ryan 1996). The model is a computer display at a museum including the visualization of models of Roman buildings and labeling some points, specially the starting point from which the user is interacting with the model.

Virtual interactivity and related concepts of "enhanced" reality are now being critized. All those references to "hyperrealities" are an evidence of artificialization. Wherever one looks, artificiality is triumphing over reality. According to Benjamin Wooley, increasingly complex, artificial environments can diminish our sense of reality (Wooley 1992). From this point we could affirm that virtual models are substituting real data, and consequently, soft images are substituting hard reasoning. V. Lull (1999) suspects that the virtual models we incorporate into archaeological research are the product of, and, at the same time, the producers of the new style of life, in which rigorous, scientific observation takes second place to the accurate, graphic transfer of images, or the precision or definition, with which they are processed. There is a danger that our public face will become a mere simulacrum, behind which is hidden our own technocratic image, consisting of drawings, photography, animation, or three dimensional images, and which will gradually become the identity card of all those who forget that it is merely a club-membership card. What are the objectives of archaeological research: to find the means to illustrate, or the means to investigate? Enhanced Reality is being substituted by an "encapsulated" reality (a term by Silvia Gili) an artificial bubble of reality, clean of noise, and prettier than reality itself.

Visualization designers must determine what phenomena need to be "visualized", and the form of the representation, so that the defined communication objectives (cognitive tasks) will be achieved. One taxonomy dimension which may facilitate this process is the following list (Tuk 1994: 29-30):

·Phenomena visualization: depiction of man-made phenomena recorded in terms of either point, local or global variables. An archaeological example is human settlement in a territory

·Meta-phenomena visualization: Display of the content/coverage, quality accuracy, etc. of a particular phenomenon. An example is the accuracy of human settlement evidences at different locations (probability values based on artifacts dispersion)

·Phenomena change visualization. Depiction of phenomena change over some specific time period, or the rate of change of a phenomenon or one of its attributes. An example is the change in frequencies of hunted animals bones in archaeological sites at specifc location and areas across time.

·Visualizations of relationships between phenomena. Display of specific, spatially based, relationships between phenomena of interest. An example is the pattern of correlations between the built environment (houses) and the volume of rubbish accumulated in each room for a set of occasions in a study area

·Causal visualization. Depiction of cause-effect relationships, known or inferred, involving the phenomena, for example the relationship between intensification of production (quantity of tools and means of production) and the architectonic complexity of houses and buildings.

·Meta-causal visualization. Displays of the reliability, validity, etc. of inferred causal relations.

·Information systems structure visualization. Depiction of the information system analysis/display functionality, for example the software modules needed to compare two different datasets.

·Analyses process visualization: Graphic depiction of the process of analysis used to generate a particular visualization, for example the surface interpolation algorithm used.

·Motivational visualization. Graphic displays designed to catch and hold the viewer's attention.

Computer graphics is engineering, not science (Musgrave 1994). The goal of engineering is to construct devices that do something desirable. The goal of science is to devise internally consistent models that reflect, and are consistent with, the behavior of (external) systems in Nature. Science informs engineering. But engineering is an ends-driven discipline: if the device accomplishes what it is intended to accomplish, it works as is therefore "good". The means by which it accomplishes its end are of secondary importance. According to Musgrave: "the degree of preoccupation with accuracy and logical consistency that marks good science is not admissible in our engineering discipline; we have a job to get done (making a picture); getting that job done takes precedence. Scientific models ('physical' models, in computer graphics parlance) do not generally map well into efficient algorithms for image synthesis. Given the aims and methods of science, this is not surprising: algorithmic computatbility and/or efficiency are not considerations in constructing scientific models" (Musgrave 1994: 264)

Selected references of virtual reality in archaeology

ALGORRI, M. E., SCHMITT, F., 1996, "Surface Reconstruction from Unstructured 3D data" Computer Graphics Forum 15 (1): 47-60.

CHALMERS, A. G., STODDART, S., BELCHER, M., DAY, M, 1997, An Interactive Photo-Realistic Visualisation System for Archaeological Sites (http://www. cs. bris. ac. uk/~alan/Arch/INSITE/research/comvis/insite2. htm)

DELOOZE, K., WOOD, J 1991, "Furness Anney survey project - The application of computer graphics and data visualization to reconstruction modelling of an historical monument". Computer Applications in Archaeology 1990, Edited by K. Lockyear and S. Rahtz. oxford: British Archaeological reports (Int. Series 565), pp. 141-148.

RYAN, N., ROBERTS, J., 1997, "Alternative Archaeological Representations within Virtual Worlds" Paper presented at the UK Virtual Reality Special Interest Group(http://www. cs. ukc. ac. uk/people/staff/nsr/arch/vrsig97/)