The Zamani Project – Preserving Rock Art “Virtually”
Dams are built across rivers and rivers attract human activities. The construction of dams is thus frequently associated with the destruction of heritage and archaeology. Well known examples are Abu Simple at the Aswan dam and the Three Gorges region of the Yangtze river. Climate changes and increases in population will undoubtedly result in the need for more dams and subsequently the need for further documentation. The laser scanning community can contribute significantly to the, at least virtual, preservation of this heritage.
Three hunter-gatherer rock art sites on the banks of the Clanwilliam dam in the Cederberg, South Africa, will soon lie under water as a result of the height of the dam wall being raised to increase the dam’s capacity. These sites, and the stories they tell through their rock art, are of great relevance for the identity and self-image of the local population, many of whom are descendants of pre-colonial hunter-gatherer communities. The rock art, which was created over the past 10 000 years, and its aesthetic value also play an important role in the creation of awareness, both nationally and internationally, of South Africa’s hunter-gatherer history. The desire to preserve these treasures for present and future generations clashes with the urgent need for increased dam capacity in a drought stricken country. Terrestrial Laser scanning makes it possible to digitally preserve the Clanwilliam rock art sites. While digital 3D recording cannot preserve heritage sites, it provides continued 3D visual access to the site as well as a virtual record for future generations. In case of the Clanwilliam sites, a further initiative towards the preservation of the rock art shelter, in the form of a physical model at a 1:1 scale, based on the laser scan data is envisaged.
The digital documentation was carried out in addition to other standard rescue-archaeology methods, such as excavations at each of the rock art sites and the surrounding areas as well as a detailed archaeological survey of the, soon to be submerged, area which contains stone tools and other evidence of early human occupation.
The Zamani Heritage Documentation Team, University of Cape Town, was tasked with the spatial documentation of sites under threat. For this purpose the mean sea level heights of the rock art in the area had to be determined in relation to the crown of the newly extended dam wall, i.e. the potentially highest level the water could reach. This was achieved with a differential GPS survey and it was established that three sites would be submerged when the water level reached it’s a maximum.
Figure 1 Screenshot of the textured 3D model of CDW10 showing the height of the new full supply dam level and the heights of highest and lowest painting. The top of the paintings will be 0.45m under water at maximum fill and the paintings will be under threat as soon as the water level rises to 95 cm below maximum.
The team laser scanned the three shelter over two days in September 2015. A total of 37 colour scans was acquired with a Z+F 5010C laser scanner. The resolution of the recorded scans was chosen so that the final registered point cloud of each shelter would have a point density of better than 1cm. Along with the scanning, and in addition to the images captured by the scanner, independent high resolution images were captured to guarantee high quality cover of the subtle details of the paintings. These images covered the entire rock surface with the areas displaying rock art being photographed at shorter distances. These images were used for texturing the meshed 3D model. Following standard Zamani documentation procedures, a number of 360 degree full dome panoramas was also acquired at each site.
The Zamani team then created a 3D meshed model of each shelter using its 3D meshing pipeline, developed by the team over a decade of recording heritage sites and based on a combination of commercial and in-house software applications. This involves cleaning and registering each scan, preparing the scans for meshing and the subsequent production of the 3D model. Positions and orientation of the independently acquired images were then determined and the images were projected to texture the model. The panoramas taken at each site were stitched together and incorporated into panorama tours where a user can move from panorama to panorama to visually experience the site.
Figure 2 part of one of the rock art panels showing human figures and animals
It is planned to generate a true to scale physical model of one or more of the sites and display the model(s) in a visitors centre near the dam wall. This centre would be a focal point for cultural tourism in an area rich of rock art shelters. It is also under consideration to cut panels with paintings out of the rock surfaces and move these to the visitors centre. Should this prove possible, it would save the rock art itself, the experience for the visitor of the public display could be enhanced significantly if the panels are built into the to scale models.
The Zamani project (http://www.zamaniproject.org) at the University of Cape Town digitally documents sites in Africa and the Middle East . An interactive 3D model of one of the documented rock shelter can be viewed on http://www.zamaniproject.org/index.php/south-afrika-3d-model-of-cdw10.html .