Applying unmanned aerial vehicle photogrammetry for measuring dimension of structural elements in traditional timber building Gi Young Jeong ⇑ , Tan No Nguyen, Dang Khai Tran, Thi Bich Huyen Hoang Department of Wood Science and Engineering, Chonnam National University, 77 Yongbongro Bukgu, Gwangju 500-757, South Korea article info Article history: Received 7 May 2019 Received in revised form 25 November 2019 Accepted 11 December 2019 Available online 17 December 2019 Keywords: Unmanned aerial vehicle 3D modeling Aerial photogrammetry Point cloud Traditional timber building abstract The goal of this study is to evaluate the application of unmanned aerial vehicle (UAV) photogrammetry to reconstruct a 3D model for dimensional measurements of traditional timber buildings. To evaluate the reliability of UAV photogrammetry, the dimensional measurements of a sample timber building from electronic distance measurement and measuring tape methods are compared to the results from UAV photogrammetry. To calibrate UAV photogrammetry parameters such as image shooting rate, camera angle, flight speed, and flight height, different variations of these parameters are applied. The best recon- struction for a timber structure is found at an image shooting rate of 2 s, flight speed of 1 m/s, and a cam- era angle of 45 degrees. Using these parameters, the structural elements of a traditional timber building are measured. Differences in the dimensional measurements of the columns and beams between the con- ventional methods and UAV photogrammetry ranges from 0.21% to 0.91%. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction Traditional timber buildings are part of the cultural heritage and have been preserved to retain the history of the country and the ancestors in South Korea. Due to their unique structural and architectural features, traditional timber buildings make priceless contributions to the current and future generations. These features reflect the cultural diversity of the past generations. However, the cultural value of traditional timber buildings have been threatened by unexpected loads and damage, such as earthquakes, wind [1–3] and wood deterioration due to insect and/or fungi attack [4,5]. To preserve traditional timber buildings, hands-on measurements of structural elements using a measuring tape (MT) and electronic distance measurements (EDM) are commonly used. From the geometric information provided by the conventional approaches, 2-dimensional (2D) have been constructed for traditional timber buildings to help maintain the buildings. Obtaining geometric information from traditional timber build- ings using hands-on measurements with MTs requires a significant amount of time and may put the inspector in danger when higher locations in the building are measured. EDMs needs reference target points attached to the surface of the building, which influ- ences the aesthetic features of the building. The stages used for EDM are on the ground level, so it is difficult to measure the roof area and sometimes the targeted structural elements are blocked by other structural elements. Surface conditions of the structural elements, such as cracks or gaps, and undulated surfaces, may influence the EDMs. Sometimes, structures around the target building prevent the application of EDM. To overcome the limitations of conventional approaches, unmanned aerial vehicle (UAV) photogrammetry approaches were considered in this study. UAV, equipped with a high-resolution camera, allows for the rapid inspection of the entire structure, an advantage over the conventional approaches that are restricted to higher parts of the structures and are time-consuming for large-scale sites. Over the past years, UAV has been used to survey various structures [6–13]. Agera-Vega et al. [6] investigated extreme topography near roads using UAV photogrammetry. Erenoglu et al. [7] studied a cultural heritage site using different camera systems including digital, thermal, and multi-spectral cameras. Deterioration of the structure was found using the ther- mal camera and inappropriate preservation of the structure was observed by the multi-spectral cameras. Metni and Hamel [8] investigated the cracks in a bridge using UAV. D’Oleire-Oltmanns et al. [9] investigated soil erosion using UAV photogrammetry and satellite image photogrammetry. From the results, they pro- posed that multi-scale mapping for soil erosion can be achieved using UAV photogrammetry. Li et al. [10] reported using UAV pho- togrammetry on large-scale urban buildings. Buffi et al. [11] applied UAV photogrammetry to survey the Ridracoli dam. Zhang et al. [12] investigated power lines along power towers using https://doi.org/10.1016/j.measurement.2019.107386 0263-2241/Ó 2019 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: gjeong1@jnu.ac.kr (G.Y. Jeong). Measurement 153 (2020) 107386 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement