Integration of photogrammetry, computed tomography and endoscopy for gyroscope 3d digitization

Abstract

Cultural heritage preservation via 3D digitization is becoming more and more important. Besides conventional buildings and landmarks, many technical instruments and artifacts, which belong to tech heritage (TH), are also of great importance, historically and didactically. Gyroscopes, which can be dated back for 200 years, are fascinating instruments with complex structures and different working principles. With such properties, any 3D digitization of Gyroscopes could not be realized by simply using conventional solutions of photogrammetry or laser scanning. In our work, we introduce photogrammetry, endoscopy and computed tomography (CT) for an integrated 3D digitization solution. Though photogrammetry has been widely used for the purpose of cultural heritage preservation, 3D reconstructions using the other two sensor systems have their own challenges. For an endoscope, a pre-calibration solution has been put forward and the Structure-from-Motion (SfM) process has been optimized to deal with the drift caused by a long imaging trajectory. Regarding the CT 3D reconstruction, we mainly focus on the 3D representation's completeness and the denoising process. In the section of data integration, we designed different methods according to the characteristics of the objects as well as the 3D models from different sonsors. In case of limited overlap between the pair of point clouds, the Gauss-Helmert model with manually picked control points is applied for the estimation of the transformation matrix. CT point clouds, which hold only the intensity values representing the material attenuation, could be integrated with photogrammetry data via a surface color mapping method using the photogrammetric images or the primitive based corresponding virtual control points. Through our research, the concept of integrating photogrammetry, endoscopy and CT for 3D digitization of Gyroscopes is validated. Furthermore, advantages and disadvantages involved in the complete process are discussed and a solid foundation has been laid for further research.