## 1 Introduction
Therefore, we propose a new approach to generate a wide-view borehole-wall cylindrical panorama from the video taken by AVBCS, converting the forward motion to translational motion in respect of the motion vector estimation. In the first step of this method, the drilled hole center of front view images acquired from borehole videos will be automatically positioned. The purpose is to decrease the image geometric distortion caused by camera vibration and to prepare the unfolding center for the next unwrapping process. The video image sequences are then unfolded into the corresponding rectangular image sequences by the proposed video sequence unwrapping algorithm. Finally, after invalid frames are removed, the rectangular \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Device** &
\begin{tabular}{c} **Probe Diameter** \\ **(mm)** \\ \end{tabular} & \multirow{2}{*}{**CCD Pixels**} & \multirow{2}{*}{**Color (Bits)**} & \multicolumn{2}{c}{**Borehole**} & **Test Velocity** \\  & & & & **Diameter (mm)** & **(m/min)** \\ \hline DPBCS [4] & 45 & \(795\times 596\) & 16/24 & 48–180 & 1.5 \\ AVBCS [5] & 25 & \(320\times 240\) & 16/24 & 28–250 & 0.8 \\ Introscopic camera [6] & 50 & \(1280\times 720\) & 16/24 & \(>\)60 & \(\backslash\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical specifications of different devices. images are used in the image mosaic process, and with the proposed projection transformation sum of the absolute difference (PTSAD) algorithm, a single wide-view borehole-wall unfolded image will be produced. Innovations of our work are as follows: (1) The proposed method created the complete borehole-wall cylindrical panorama from forward-looking borehole videos, which expands the application fields of the AVBCS system. This may also inspire technical innovations of pipeline inspection, nondestructive evaluation of gun muzzles, image analysis of medical endoscopic video and so on. (2) The drilled hole center of the borehole-wall image is automatically located by the proposed borehole center location algorithm, which eliminates the impact caused by the camera trajectory not being along the central axis of a drilled hole. Furthermore, the proposed virtual coordinate graph (VCG) is applied together with the coordinate mapping algorithm (CM) to construct the rectangular image sequence from the forward-looking borehole video. (3) The matching of the rectangular image sequence is the critical part of generating a complete borehole-wall cylindrical panorama. To enhance the efficiency and accuracy of the video image matching, we propose a template matching algorithm based on the sum of absolute difference (SAD) and gray projection transformation (GPT), which is referred to as the projection transformation SAD (PTSAD) algorithm. The paper is organized as follows: The related work is reviewed in Section 2 and an overview of system descriptions is described in Section 3. Section 4 gives the description of the approach to the center location of borehole-wall images, the generation of borehole-wall unfolded images and the mosaic of borehole video images based on the proposed PTSAD algorithm. The experimental results and analysis are shown in Section 5, in which our proposed method is tested using actual borehole videos. Section 6 presents the conclusion.