Lost in Space : 3D modelling, visualisation and analysis techniques for ground-penetrating radar data in 3D GIS

Sammanfattning

Archaeology and archaeological sciences are inherently spatial disciplines. Thus, it is of no surprise that GIS (Geographic Information System) has found its way into archaeological practice, providing an environment for data organisation, analysis and visualisation. Over the past few decades, archaeogeophysics has become an integral part of archaeological practice. The results of these studies are traditionally examined in a 2D GIS environment, utilising 2D polygons, even though the targeted features are 3D structures. Despite the recent shift towards 3D GIS environments, the interpretations of geophysical prospections have remained in the realm of bi-dimensionality. This prevents the full exploitation of the 3D potential, especially of ground-penetrating radar (GPR). In this thesis, three modelling approaches are presented, derived from two different concepts. The proposed framework was tested on data from the archaeological site in Blera, Italy. On one hand, the polygon model is derived from polygons created during the standard geophysical interpretation process. Thus, the model does not represent the subsurface itself but rather an interpretation of it. The processing time is just a couple of seconds. On the other hand, the cube and mesh models are derived from the GPR point cloud filtered by amplitude strength, creating iso-surfaces. They visualise certain portions of the ground with chosen properties. As the cube model can have a long processing time, the mesh model is an alternative modelling technique for larger datasets. All three models were successful at visualising linear features. These models are analysed in a 3D GIS environment, focusing on spatial, statistical and exploratory approaches. The utilisation of different symbologies facilitates the understanding of models´ properties. Combinations of the models with a digital terrain model, as well as depth slices, provide a topological context for the models and information about the modelled anomalies. Modelling and analysing GPR in 3D poses an advance for both academia and commercial archaeology by improving the assessment of excavation logistics. Moreover, the balance between cultural heritage management and land development is facilitated. Lastly, the models can be used for public outreach through interactive exhibitions.