Non-contact restoration of missing parts of stone Buddha statue based on three-dimensional virtual modeling and assembly simulation

Abstract

Three-dimensional (3D) digital technology is one of the most essential conservation methods that complements the traditional technique of the restoration of cultural artifacts. In this study, 3D scanning, virtual restoration modeling, and 3D printing were used as a non-contact approach for the restoration of a damaged stone seated Bodhisattva (stone Buddha statue). First, a three-dimensional model with an average point density of 0.2 mm was created by integrating the fixed high-precision scanning of the exterior and the handheld mid-precision scanning of the interior excavated hole. Through a 3D deterioration map of the stone Buddha statue, the area of the missing parts was measured as 400.1 cm 2 (5.5% of the total area). Moreover, 257.1 cm 2 (64.2% of the missing part area) of four parts such as the head, the surrounding area of the Baekho, the right ear, and the right eye, for which symmetry was applicable for modeling or there could be ascertainable historical evidence for the total missing parts, was selected for restoration. The virtual restoration of the missing parts of the stone Buddha statue was performed using a haptic modeling system in the following order. First, the location of the three fragments detached from the head was determined. Next, the reference model was selected, and its symmetrization and modification with respect to the original were conducted. Also, estimation modeling and outer shape description were performed through historical research and consultation with experts. The created virtual-restoration model’s (461 cm 3 ) heuristic-based assembly suitability was verified by design mock-up printing and digital–analog simulation. In particular, to address the assembly interference, the interface surface was modified and reprocessed several times. Accordingly, the final design mock-up’s volume size was decreased by 5.2% (437 cm 3 ). Photopolymerization 3D printing technology was used for the actual restoration of the stone Buddha statue and the layer thickness of the material used was set as 0.10 mm considering the surface roughness. Finally, the surface of the printed output was colored to prevent yellowing and joined to the missing part of the stone Buddha statue. This study presents a great case to shift from the traditional manual-contact method to the contactless digital method for the restoration of artifacts and is expected to largely contribute to increasing the usability of digital technologies in the restoration of cultural artifacts.