Proposal of the Use of Differential Render in Rebar Inspections

In Japan, the number of people working in construction has been decreasing yearly since peaking in 1997 because of the declining birthrate and aging population. The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) is promoting i-Construction, which aims to increase productivity by using ICT (Information Communication Technology) across the entire construction industry. In particular, the use of ICT is expected to be applied to the inspection of reinforcement rebars, which form the basis of all concrete structures, as the inspection of reinforcement bars has become stricter due to the influence of the structural calculation falsification problem that occurred in 2005. The existing methods use image triangulation to obtain a 3D point cloud of the rebar surface, so depending on the lighting conditions and the arrangement and shape of the rebars, there are some sites where it is not possible to obtain a sufficient number of point clouds, and thus the range of application is limited. This paper proposes a method for using rapidly developing differentiable rendering technology for rebar inspection. Since differential rendering makes it possible to reproduce free viewpoint images, it is possible to inspect the rebar even if the distance to the rebar surface cannot be directly measured, as long as it is possible to reproduce the appearance of the rebar as seen from a viewpoint in 3D space. Image inspection can be expected to become more versatile than before. This paper reports on the evaluation of accuracy and systematization schemes.