Towards the Rapid Documentation of the Tanum Landscape: Developing an integrated workflow using 3D laser scanning and image based modelling techniques

Abstract

The Tanum World Heritage Area, located in northern Bohuslän ca. 150 km north of Gothenburg, Sweden, is a multifaceted land-scape containing remnants of human activity from the Neolithic to Modern Historic times. This area is particularly famous for its well-preserved rock art, with no less than 1,500 recorded localities containing thousands of images (Ling, 2008, 5) dat-ing mainly from the Bronze Age, covering over 1,200 years (ca. 1700 – 500 BCE). To date, documentation efforts in the area have focused primarily on the recording and preservation of these rock carvings, and while other components of the land-scape have certainly not been neglected, a byproduct of this ac-tion has been that in some ways the carvings themselves have become divorced from the larger cultural and physical context of the region. Therefore, a prime goal of any new research in the region should be to focus on the documentation of the area from a landscape perspective, including the recording of all presently surviving elements of past land use at all scales. No less impor-tant is the need to develop an effective way to monitor the condi-tion of archaeological recourses in the Tanum area in order to as-sess the true impact of accelerated degradation due to exposure, pollution and high visitor traffic. Recent advances in 3D docu-mentation technologies, including 3D laser scanning and image based modelling techniques, can provide solutions to these is-sues by offering integrated and complementary ways to rapidly record, process, archive and share data from a landscape to a fea-ture level, making them ideal tools for the recording of all facets of the Tanum region. A complete documentation and analysis of the Tanum area has to be seen at different scales. Firstly, a topographic model based upon airborne laser scanning (ALS) data forms the basis of any further spatial analysis. High-resolution terrain models con-structed from ALS data can be used for the detection of past land use at an intersite to site scale, and can also be used for the effec-tive estimation of shoreline displacement due to glaciations and land uplift. Secondly, terrestrial laser scanning (TLS) techniques can be used at a site to intrasite level to provide detailed record-ing of individual archaeological features in the landscape, such as rock cairns, rock carving panels, and even individual carving outlines (Figure 1). Finally, image based modelling techniques such as structure from motion (SfM) and multi-view stereopsis (MVS) as well as high-resolution handheld laser scanning can be used to record individual features and provide detailed docu-mentation of feature elements including the precise (50 µm) re-production of structure within the features. This might shed light on the initial creation processes. All these datasets can then be combined to form a multiresolution model of the Tanum land-scape, providing rapid access to information at varying scales and for various purposes.