摘要
作為交通和道路系統的關鍵組成部分，橋梁在人類生活和國家經濟方面發揮著重要作用。其中在箱型橋梁的內部，因空間狹小、環境惡劣且完全黑暗，因此人員現場檢測時需要使用照明進入內部才能以人眼進行目視檢測，此過程有礙身體健康且繁瑣又耗時。
為了將劣化檢測成果進行三維橋梁空間的定位，當前有關 3D模型的重建方式大都以地面雷射掃描儀 (Terrestrial Laser Scanning, TLS)和近景攝影測量為主。然而，TLS儀器較為昂貴且有些體積大不易攜帶。因此本研究建議使用由具有 360 視場角 (FoV)之多魚眼相機裝置，組成的低成本儀器來拍攝與製作箱型梁內部之 3D模型。
本研究重點之一為相機之預校準(Pre-calibration)，特別是相機之內方位參數（IOP）和相機間的相對方位參數（ROP）。本研究採用自率光束法平差(Self-calibration bundle adjustment, SCBA)技術來實現精確預校準。此技術使用Australis 編碼後之人造標，有助於確保預校準參數的準確性。
本研究另一個重點是，在箱型梁長廊道的弱幾何影像網型下，如何使用多魚眼鏡頭重建出高精度的三維模型。本研究數據採集路徑呈直線，以提升取像之效率。實驗中以球形全景模式和原始未拼接的預校準影像，在地下室全黑長廊區域進行模擬，在LED燈輔助下進行拍照，同時計算與評估合適的重疊率，以便在進行箱型梁內部數據採集前，先行了解最佳的攝影方式。
在實際箱型梁內部實驗中，本研究選擇了兩跨箱型梁測區，兩測區均位於橋梁的起點。第一個測區有比較多的塑膠管道佔據空間，影響了3D建模的完整性。實驗中還進行了直線軌跡和環型軌跡的數據採集程序，但在空三平差後，皆獲得了小於1公分的尺度檢核誤差。此外，在3D密集點雲精度分析中，進行了點雲與點雲距離的計算，結果在兩個測區分別得到3.56公分與1.4公分的平均誤差，以及2公分的均方根誤差，顯示本研究能夠生成具有高幾何精確度的密集點雲，而所建議的方法與低成本設備，可應用於高精度的室內測繪。
本研究主要貢獻，在於即使沒有任何比例尺(長度)或控制點的約制，以準確且穩定的預校準參數針對長廊道區域重建 3D模型，有機會獲得高精確度的 3D 模型。而透過本研究所建議的低成本攝影儀器，配合近景攝影測量技術，有望作為取代現場人員目視檢測的替代解決方案，特別是在沒有任何照明的長廊道區域 。

Abstract
As a key component of transportation and road systems, bridges play an important role in human well-being and improve the economy of a country. However, the inside parts of the bridges, i.e., the box girder, which is in a narrow space and totally dark, are rarely inspected, sometimes through manual inspection by illuminating the inside part of the infrastructure, which is tedious and time-consuming. Since this technology offers an accurate solution, the current literature on 3D reconstruction is dominated by terrestrial laser scanners (TLS) and full-frame cameras. However, this instrument is not a portable option and demands substantial investments in terms of equipment purchases. In practical experience, a low-cost instrument composed of a multi-fisheye camera rig with 360-degree field of View (FoV) coverage is suggested to produce a 3D reconstruction of the box girder.
This study focuses on camera calibration, specifically the calibration of Interior Orientation Parameters (IOPs) and Relative Orientation Parameters (ROPs). A suitable technique called Self-Calibration Bundle Adjustment (SCBA) is employed to achieve accurate calibration. This technique is assisted by Australis-coded targets, which help ensure stable pre-calibration parameters. By implementing this approach, the study aims to obtain reliable and precise camera calibration for subsequent 3D reconstruction tasks. The video sequence mode is utilized, and the data acquisition path is in a straight line with forward and backward directions for faster and more efficient purposes. This experiment performs the simulation in a long corridor area with spherical panoramic mode and from original unstitched pre-calibrated images. The second simulation is conducted by masking and configuring the overlap ratio assisted by an LED light in a location without any illumination to represent the condition of the environment and get the best configuration before performing data acquisition inside a box girder.
In a box girder, this study uses two samples of the box girder, both of which are located at the starting point of the bridge. The first road is more covered by pipelines than the second road. This experiment also conducted two data acquisition procedures: straight line and surrounding track data acquisition. Regarding this experiment, it obtained a CkSB error of less than 1 cm. Furthermore, for 3D accuracy evaluation, C2C was conducted, and this study was able to generate point clouds with high geometric quality as the references and the point density are quite similar to the ground truth, and it yielded a mean error of 3.56 cm in the first road and 1.4 cm in the second road, with the RMS error less than 2 cm RMS compared to TLS. Regarding the result, this approach may suggest sufficient and acceptable indoor mapping with low-cost equipment. The main contribution of this research emphasizes that accurate and stable pre-calibration is important to obtain highly accurate 3D reconstruction results and offers accurate scale factors, even though without any scale bars or control points, to generate 3D reconstruction in a straight-line long corridor area by obtaining a mean error and RMS error around 1 cm in the C2C comparison. Furthermore, the proposed instrument may be interesting to replace in-site inspection methods, and a close-range photogrammetry method that offers accuracy while reducing cost is promising as an alternative solution to replace in-site inspection, especially in an indoor area without any lighting.

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