3D Laser Scanning-Based Automated Wall Surface Flatness Inspection

Indoor wall surface flatness is a mandatory acceptance item in building decoration work, but it is still commonly checked using a 2 m straightedge and a feeler gauge. This manual method samples only a limited number of locations, depends on inspector judgement, and provides no full-surface spatial record. This study proposes a terrestrial laser scanning (TLS)-based automated workflow for wall surface flatness inspection that remains consistent with the Chinese national standard GB 50210-2018. After point-cloud registration and wall segmentation, a least-squares best-fit plane is established for each wall, and the signed point-to-plane deviation field is computed. A virtual 2 m straightedge operator is then applied at multiple positions and orientations to reproduce the code-defined measurement in which the maximum gap under the straightedge is taken as the flatness reading. The method was validated against paired manual measurements on a reference wall, showing a mean difference of 0.00 mm, a standard deviation of 0.20 mm, an RMSE of 0.20 mm, and a correlation coefficient of 0.98, with identical accept/reject decisions at the 4 mm limit. A residential case study involving four inspection zones and 42 measurement points further demonstrated that the workflow can generate code-comparable flatness readings, full-surface deviation maps, and localized rework guidance. The overall pass rate was 92.9%, with all non-conforming points concentrated in the living room, and the on-site inspection time was approximately halved compared to manual checking. The results indicate that the proposed TLS-based virtual-straightedge method provides a practical, traceable, and standard-compliant alternative for automated wall surface flatness acceptance.