A computer-assisted constraint-based system for assembling fragmented objects

Abstract

Abstract-We propose a computer-assisted constraint-based methodology for virtual reassembly of Cultural Heritage (CH) artworks. Instead than focusing on automatic, unassisted reassembly, we targeted the scenarios where the reconstruction process is not be based on shape properties only but it is build over the experience and intuition of a CH expert. Our purpose is therefore to design a flexible interactive system, based on the selection of a set of constraints which relates different fragments, according to the understanding and experience of the CH operator. Once the user has defined those constraints, the system searches for a suitable solution, using a global energy minimization strategy that considers simultaneously all the pieces involved in the reconstruction process. Additionally, our framework provides the possibility to work in a hierarchical way, mimicking the traditional physical procedure that archaeologists use to reassemble tangible fractured objects. The frameworks is designed to work even with fragments that could have been severely damaged or eroded. On those datasets, automatic approaches may often fail, since the fractured regions do not contain enough geometric information to infer the correct matches. We present some successful uses of our framework on real application scenarios.

Pairwise Alignment of Archaeological Fragments Through Morphological Characterization of Fracture Surfaces

“…Moreover, their digital mesh representation may contain digitization noise and point cloud registration errors from the 3D scanning process. These demands, paired with a sensible time behaviour, make pairwise alignment a daunting computational task (as other studies such as (Toler-Franklin et al, 2010;McBride and Kimia, 2003;Palmas et al, 2013) confirm).…”

Automatic Reassembly of Fragments for Restoration of Heritage Site Structures

“…The extent of automation also varies for different works. A few works require the user to specify initial constraints like iso-planarity, adjacency while others do not involve the user at all and perform a completely automatic reassembly [12] [14]. We use very low user intervention in the following processes: (1) to finalize the pairwise and (2) reject the match when overlaps occur during global reassembly.…”

Boundary Morphology for Hierarchical Simplification of Archaeological Fragments

“…Such simplifications are strongly related to characterizing a surface by differential geometric features, such as those computed by some means of discrete differential geometry [7]. Indeed most methods to reassemble broken objects [12,14,18,20,26] are based on such features. However, a small chip, resulting in a missing part of an object, will affect such differential measures in a linear fashion: the deeper the missing bit, the stronger the simplified shape is affected.…”