Pairwise Alignment of Archaeological Fragments through Morphological Characterization of Fracture Surfaces

This thesis presents a complete pairwise alignment framework for archaeological fragments through morphological characterization of their fracture surfaces. Our research was performed within the context of the GRAVITATE project, which aims at providing archaeologists with virtual tools to analyse digital artefacts distributed across several collections. We study in depth how the non-linear capabilities of Mathematical Morphology (MM) can be employed to fracture surface simplification, representation and alignment. We explore the principles of Mathematical Morphology and develop the core theory required for applying morphological operations to complementary volumetric objects. To enable the morphological simplification of the archaeological fracture surfaces, we develop the novel ‘Boundary Morphology’ (of surfaces rather than volumes). In our approach, the fracture surface is tightly bounded by a concise set of characteristic multi-local morphological features. This morphological representation provides the information required for accurately aligning the fracture surfaces through applying a RANSAC-based algorithm incorporating weighted Procrustes to the morphological features. A refined version of ICP (Flank-ICP) is also proposed, which works exclusively on the morphologically defined flank regions of the fracture surface. These regions were proved to be more stable than the peaks and valleys for alignment. We propose new criteria for evaluating the resulting pairwise alignment quality, taking into consideration both penetration and gap regions. We evaluate our method on real terracotta fragments from the GRAVITATE dataset through careful quantitative evaluation. We show that by using the most significant and effective morphological features, our method outperforms a recent linear pairwise alignment method. We briefly discuss our limitations and the effects of variations in digitization and abrasion on our proposed alignment technique. Our novel MM representation is shown to be insensitive to the kind of missing information and abrasion prevailing in archaeological fragments, enabling the accurate and robust alignment of fracture surfaces.