Computer Graphics in Archaeology

Paula Monteiro1

1 MAP-I PhD Student

Abstract. The computer graphics and archaeology began a relationship in which the techniques and tools of computer graphics were made available to the archaeology to allow the reconstruction and visualization of the archaeological findings. It allows also the preservation of the archaeological sites from the damage caused by some archaeological works that can be now replaced by a computer based work.

Keywords: Computer Graphics, Archaeology, Virtual Reality, Augmented Reality, 3D modeling.

1 Introduction

Computers have become an indispensable tool in our life. They have been used for long time in archaeology to record the excavations plans, to illustrate the artifacts found and to present the results of the analyses.

The definition of Computer Graphics in the Wikipedia says that Computer Graphics “is a sub-field of computer science and is concerned with digitally synthesizing and manipulating visual content. Although the term often refers to three-dimensional computer graphics, it also encompasses two-dimensional graphics and image processing”.

Archaeology is defined in the Britannica Concise Encyclopedia as a “Scientific study of material remains of past human life and activities. These include human artifacts from the very earliest stone tools to the man-made objects that are buried or thrown away in the present day. Archaeological investigations are a principal source of modern knowledge of prehistoric, ancient, and extinct cultures. The field emerged as an academic discipline in the late 19th century, following centuries of haphazard antiquarian collecting. Among the archaeologist's principal activities are the location, surveying, and mapping of sites and the excavation, classification, dating, and interpretation of materials to place them in historical context”.

Computer graphics is one important tool to represent and manipulate large quantities of data with a high level of complexity. In archeology we have a large set of data, complex data, that benefits in being represented using the powerful techniques of the computer graphics.

The advances of computer graphics has provide several powerful tools to treat and model the data collected and recorded by the archaeologists helping them in the tasks they have to perform as an archaeologist. With this powerful tools provided by computer graphics, is now possible to visualize and reconstruct an archaeological site

and archaeological artifacts. This visualization and reconstruction would be an almost impossible task without this computer graphics help.

The fields of archaeology and heritage, once those areas are related, have benefited from the new possibilities resulting from the introduction of computer graphics in there work. Another advantage of the use of 3D models of archaeological artifacts and places is that: people can see the past constructions, they can see it from various directions instead of only one like in pictures, the degradation caused by the natural factors and man can be eliminated and finally people can see this through the internet [1].

The following section presents some of the works that have been done in Computer Graphics to be used in Archaeology. It starts by describing the first works done in this area in the end of 70’s until the beginning of the 90’s. Next, are described the works that creates and implements virtual reality for the archaeology. The same is done for the augmented reality works. The last sub-section presents a group of works that have faced the problem of the realistic illumination of the archeological sites. Finally some conclusions.

2 Computer Graphics in Archaeology

2.1 Earliest works

The relation between computer graphics and archaeology starts in the end of the 70’s [2]. The goal of this relation was to implement an interactive system to assist the archaeologist in the analysis of the distribution of the artifacts from an excavation site. The need to use this system to help the archaeologist in the analysis of the artifacts appears by the fact that an archaeological excavation is a destructive process. The layers that compose an archaeological site can vary from depth and thickness which can lead to a not very correct chronologic interpretation of the artifacts.

To help the archaeologists in solve this problem was created a system using a color display and presents to the user three scenarios: site plans, vertical sections and legends. The plans are cylindrical volumes, sections are slices of arbitrary thickness through a plan and the database stores the artifacts information. However the fundamental operation of this system was the presentation of the objects existing in a plan or section (fig.1).

Fig. 1. Plan display and Section display [2].

Few years later, in the end of the 80’s another project [3] put the computer graphics techniques to available to the archaeologists. Like the previous one, the motivation to develop this project was the fact that in the archaeological excavations to show what is below it have to destroy what is placed above. In the excavations the archaeologists cannot see the complete formation that is being analyzed. There are also some moments in which they cannot see anything because part of the objects of the excavation was removed and part is still under the surface. To help archaeologists to get a complete image of the excavated site it is necessary to integrate the different layers of the excavated objects.

Using computers it was possible to create a virtual reconstruction of the site by combining a relational database and sophisticated graphics facilities. One example of this relation is the Winchester Graphics System (WGS) [3]. In this system the data stored in the database has associated a three-dimensional position coordinate, an orientation and a set of additional attributes. All the records can be associated to three-dimensional coloured markers and lines. Those lines and markers are then displayed allowing the archaeologist to see the spatial distribution of the artifacts selected. This system was demonstrated on the Bronze Age pits from Altheim in Bavaria, on the objects found on the rubbish pit at the mid-Saxon settlement of Hamwic and finally on the Bronze Age midden from Potterne in Wiltshire.

In this decade computer graphics was used to reconstruct history by creating images and animations to be presented in television programs. One example of this was the creation of images of the Roman temple site below the Pump Room in Bath [4]. To create those images it was used a ray-casting algorithm. The created images were included in a BBC prime-time program in 1984. This was one of the first applications of computer graphics and solid modeling to be applied to the archaeology, in particular to the archaeological reconstructions.

2.2 Virtual Reality

Virtual Reality is an alternative that was presented to the archaeologists to the excavations and related tasks that have to be performed in an archaeological site. Beside this importance to the archaeologists work it also provides benefits to the education of archaeology and also to the museum presentations without compromise

the safety of the archaeological site. The archaeological sites and artifacts are fragile and valuable to be lost. So using these computer graphics techniques it is possible to reveal and study them without put in any kind of risk of destruction. It also reduces in the time of the work to be done in the excavation site.

Using computer graphics and in particular using virtual reality in archaeology is an important way to allow the archaeologists in their work. It does not only help the archaeologists to visualize the excavation site as it was in the past but helps also in reconstruct and visualize the artifacts. The artifacts recovered using virtual reality can be called virtual artifacts.

The use of virtual reality in the reconstruction of the artifacts is very helpful since it allows the assembling of the artifact without damage the artifact remains and even cause damages in the excavation site where the artifact was found. Another advantage of use virtual reality in the reconstruction of the artifacts is to allow the preview of the possibilities of assembling more easily, reducing errors and the time spent in those tasks. Those virtual artifacts can be used in presentations showing the importance of the discovery but without submit the real artifact to the possibility of suffer damages.

One project that uses computer graphics and virtual reality to reconstruct artifacts was presented in [5]. This project used the virtual reality to study the possibility of recover some artifacts that were buried in the Museum of the Terra Cotta Warriors and Horses, Lin Tong, Xi’an, China. The artifacts were statues buried for 2000 years so they were very damage and this will turn it assembling very complicated. To solve this problem they start to measure and scanning the artifacts fragments. After scanning the fragments, the scans obtained where converted on a mesh model, them a texture was applied and finally the virtual fragments where assembled in a representation of the original artifact. In fig.2 we can see the software used to assemble the fragments in one unique artifact and the final artifact obtained after the assembling process.

Fig. 2. Software used to reassemble fragmented relics and the reassembled virtual statue. [5].

Another project that deals with the same problem of reassemble fragment pieces from an archeological site is presented in [6]. However, in this project instead of assemble an artifact found on an excavation what have to be assembled is a monument, like the Parthenon at the Acropolis of Athens. Once again one of the

motivations to use computer graphics to help the assembling the monument is the huge number of fragments. In this project another of the motivations was the size and height of the blocks and the distance between one block and a possible match. The reconstruction can also be delay by the damage or the inexistence of a fragment. This project develops a system called Virtual Archaeologist. This system was used to help the archaeologists in reconstructing monuments or artifacts avoiding the manual test of verify if fragment match with another. The system allows the full reconstruction of the artifacts using 3D scans of the fragments. The Virtual Archaeologist (fig. 3) detects the fractured faces of a fragment and matches this fragment with the other fragments. If a match is found the fragments are assembled. The data used as input are polygonal meshes of the fragments obtained by from a 3D scanner. This is a system that does not need intervention from the archaeologist but if he wants he can interact with the system.

Fig. 3. The Virtual Archaeologist desktop[6].

There are also projects of virtual reality in the archaeology not to be only used by the archaeologist in their work but to be also used in the museums to disseminate the culture by the visitors.

A project created by the greek Foundation of the Hellenic World (FHW) [7] creates a virtual reality exhibit to present the Hellenic culture, historical memory and tradition.

Another system to present to the tourists and visitors of an archaeological place, is the MUSE [8]. This is a 3D model virtual reality system developed to open to the visitors some historical buildings in Pompeii that were closed in order to protect them. The visitor can move himself in several directions and explore the 3D model of the place seeing it from different perspectives. The user as a tablet pc in which is simultaneous displayed two images. Those images are reconstruction models of the place, but one of the models represents the current archaeological place like it is and the other model presents a reconstruction of the building like it was before being buried by the volcano ashes. This system is used in the archaeological place. Fig. 4 shows one example of the information that is displayed in the tablet pc.

Fig. 4. Example of the MUSE [8].

In 2001 a project [9] as started and the main goal of this project was to create a system to present and store the archaeological data collected by the archaeologist during the many years of the archaeological expedition. This system is called Virtual Archaeology and it will be used in exhibitions and museums. It consists in display a 3D model of the landscape with the archaeological site already reconstructed and in some points of the exhibition some other 3D models can be included. This is a system that has to be used in an auditorium. This system was applied in Troy, an archaeological site in a very bad state of preservation. In fig. 5 we can see an example of a scene of the demonstration, in which we see the reconstructed houses in Troy and an extra 3D model included, in this case the man.

Fig. 5. Reconstructed houses and (hyper)realistic man in Troy [9].

Another way found to bring visitors to a museum was to take the museum to the visitors. This was possible using the virtual reality over the internet [1]. One example of a creation of a virtual museum was done for the pit No. 2 of the museum of Qin Shihuang Ceramic statues Warriors and Horses in China.

The Petra Great Temple archaeologists where involved in a collaborative effort to create new archaeological analysis tools [10]. With these tools it was intended to give to the archaeologists access to parts of the archaeological record which were inaccessible before, to support the navigation and interaction with virtual archaeological artefacts and architecture and to preserve the space before the

excavation. To accomplish the creation of those tools 4 prototypes where created each one more refined than the previous one. The final prototype provides a model of the archaeological excavation site which can help the archaeologists to visualize all the data collected on this excavation site.

Archaeologists spend lots of time drawing plans and maps, taking notes and taking pictures of the archaeological findings. This information as said before is important to preserve the archaeological artefacts from destruction. With a system described in [11] the archaeologists can create a 3D reconstruction by simply take several pictures from the artefact (pictures taken in different viewpoints) using a standard digital photo or video camera. The use of this system simplifies the archaeologist work because they have not to take measurements of the artefact to get a 3D model. In fig. 6 we can see a set of 6 images taken with a digital camera and the 3D model automatically created. The advantage of using system is the small time that the archaeologists have to spend to get the images and the fact that the models are created automatically with a high level of realism.

Fig. 6. Reconstruction of a corner of the Roman baths at the Sagalassos archaeology site. (a)

Our system used the six images (b) and automatically created the model [11].

The interest in use virtual reality is increasing because it as the advantage of have virtual models available in the internet allowing to all people to see and “walk” in a given virtual model. The Celtic oppidum Závist [12] s an archaeological site in the Czech Republic. It is also a utilization of virtual reality in the archaeology. The reconstruction where done using the data collected in the last decades by the archaeologists. The reconstruction gave origin to a VRML model that could be used by the users to walk in the site. In fig. 7 is an example of this virtual environment.

Fig. 7 Celtic oppidum Závist virtual environment [12].

In 2004 another work concerning the reconstruction of broken archeological artifacts was presented [13]. This work is a new environment for computer aided reconstruction of archaeological objects. It is also presented a new method to estimate the quality of the association between two fragments. This application follows the methodology used by the archaeologists to match the fragments. They are assembled by similar properties, like color, material, geometry, etc. However, in this application the fragments will only be matched by geometry. The fragments are scanned generating dense triangular meshes that will be used to associate the fragments. After the match of the fragments they will be evaluated to test the quality of the assembling.

2.3 Augmented Reality

Augmented reality is the combination of images generated by the computer and the real world. Normally to see an example of augmented reality the user has to wear special glasses and a computer. If it is experimenting the augmented reality in the interior of a building like a museum it can use a desktop, but in the outside it can use a portable device like, a wristwatch, a necklace, or, perhaps, embedded into clothing. [14].

GEIST [15] is a project that uses augmented reality but using the capabilities of the mobile devices. The idea of this project is to allow the users to see the history of the places while walking in the city. This system was tested in the Heidelberg castle.

ARCHEOGUIDE [16, 17] is another project that uses augmented reality. It was used in the archeological site of Olympia in Greece. This project also wants to create a system to behave like an electronic guide during the tours made by the visitors in cultural sites. It gives to the users a view of a site but with the reconstructions of the ancient ruins. The images that are viewed by the user are based on his orientation. When the user is using this system he sees 3D reconstructions of archaeological monuments and artifacts but at the same time he sees what is surrounding the monument and listens to an audio description of what he is seeing. In fig. 8 we can see an example of the original image of the site and the augmented image of the same place that the user sees.

Fig. 8. Original Image and Augmented Image from Olympia site [16, 17].

In the ARCHEOGUIDE system there is also the creation of virtual human models. Those human models were animated and used to demonstrate the execution of the sport modalities that were practiced in Olympia. In fig. 9 we can see an example of this animation.

Fig. 9. Virtual human models competing in the Olympia Stadium [16, 17].

The museums are each time more interested in get new visitors and to increase the user social experience and learning about antique artifacts and their history. One of the ways they found to this is to use virtual and augmented reality presentations in their spaces. Following this interest of the museums several projects have develop systems that put this technologies available for them [18, 19].

The system described in [18] (ARCO) is a system that allows the museums to create an virtual and augmented reality presentation in a easy and quick way. The presentations can be shown inside the museum or in the Internet. ARCO is uses X-VRML templates to create the virtual presentations. The X-VRML is a high level procedural language that adds to the virtual scene standards dynamic modeling capabilities. With this system the museums can build interactive scenarios which transform the museum visitors in active actors of the virtual and augmented exhibition. An advantage of this system is that it can get out of the museum and go to a school class. The users of the system have a new approach to explore the cultural and archaeological artifacts of the museum collections.

2.4 Realistic Illumination of the Archeological sites

With the 3D reconstruction of archaeological sites and artifacts give us the possibility to see the past. The photorealistic generated images are representations that help us to see and understand the archaeological site. However, the archaeologists are not sure if those images are physically and perceptually valid. The archaeologists are complaint about the lack of realism of some images. This appears mainly caused by the use of false ambient illumination. The images created must represent correctly the environment and should be indistinguishable from the real world.

In the ancient times the illumination was done by the daylight or using a flame. There are lots of archaeological buildings without windows, like the caves, that were illuminated with a kind of firelight (candles, oil lamp, etc)

In [20, 21] a study of the impact in an image the use of different type of light. The experiments where done in the rock shelter site of Cap Blanc and in the House of the Vettii in Pompeii. In the first example we have a shelter with horses, bison and deer carved in the wall 25000 years ago. Since this archaeological site was discovered several images were taken but the images have variances between them. Those variances were caused by the illumination. So it was decided to render images using Radiance. In fig. 10 we can see the difference of the image as you can see today illuminated by a 55W bulb and how it was seen 25000 years ago illuminated with an animal fat tallow candle.

Fig. 10. (left) 55W incandescent bulb and (right) animal fat candle [20, 21].

Analysing the two images we can see the differences. The image illuminated by the animal fat candle as more shadows that the other one. The other example used to study the impact of light in the final image we have the House of the Vettii in Pompeii, a well preserved building. This building has rich colours and extensive use of artistic techniques. But as said before in relation to other archaeological and important places the tourism and the time have caused some deterioration of this site. So it was created a realistic reconstruction of this site. In fig. 11 we can see the differences from each type of light. With this study it we can see that the type of light chosen to illuminate the scene is very important to obtain a realistic image of the site.

Fig. 11. Clockwise from top left: (a) modern lighting (b) olive oil lamp

(c) olive oil lamp with salt (d) olive oil lamp with water [20, 21].

As said before the results of the virtual archaeology to be considered realistic the lightning must be taken in account. In particular case the kind of light used in the ancient times. To accomplish this main issue of the virtual archaeology a methodology to create high fidelity reconstructions with realistic lightning [22]. The methodology includes several steps: construct a precise geometric model, detail the surface materials and textures, create a model for the light flame and rendering the model with the correct lightning. This methodology was tested in the ancient Egyptian temple of Kalabsha. In fig. 12 we have an example of the results obtained in a reconstructed hieroglyphics using two different type of light.

Fig. 12. Reconstructed hieroglyphics using (a) modern lighting and (b) a sesame oil lamp [22].

Get a precise visualization implies the use of global illumination models to render the images. This is a very demanding task in computational terms. The appearance clusters give the opportunity to achieve this goal. In [23] a framework to create virtual walkthroughs with high fidelity images using this new computational power is described. This framework is a three layer architecture, composed with a Renderer, a Visualizer and a shading management agent (SMA). As a result of this work it was created a prototype of a walkthrough in the archaeological model of the roman town of Bracara Augusta, in Braga, Portugal.

3 Conclusion

In the last years we have face an increasing number of projects and researches that uses computer graphic techniques to help archaeologists in their work.

Virtual and augmented reality is used to reconstruct archaeological sites, to preserve these sites from uncalculated damages and to help the archaeologists in the reconstruction of broken artefacts. But the virtual and augmented reality in the archaeology is not only important to the archaeologists, but it is also important to the visitors of museums and archaeological sites. Using this computer graphics tool they can see and understand the ancient place in a more interactive and animated way.

Obtaining a realist image of an archaeological site is very important to the archaeologists, so the illumination of the archeological sites are become a very important subject in the computer graphics for the archaeology.

As a final remark we can see that this relation between these two distinct areas was fruitful.

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