Remote measurement of reinforcing bar spacing and length from an oblique photograph using a novel perspective correction technique

Abstract

The dimensional inspection of reinforcing bars at construction sites prior to concrete pouring is essential to ensure structural integrity. However, this process has traditionally relied on manual tape measurements, which are labor‐intensive, unsafe, and prone to human error. To address these limitations, this study introduces a novel method for remotely inspecting the spacings and lengths of reinforcing bars using a single oblique photograph and a new perspective correction technique. This method transforms oblique images into vertical images using constraints based on four specific vectors that must be perpendicular to one another, thereby eliminating the need for the four‐point correspondence required by existing methods. This improvement enhances the practicality of the proposed method. A validation experiment conducted at an apartment construction site yielded a mean absolute error of 5.12 mm in measuring the spacing and length of reinforcing bars, demonstrating field‐level accuracy in compliance with American Concrete Institute 117 and the Gagemaker's Rule from US military standard 120.