Omnidirectional (360°) cameras are being increasingly used for recording and presenting a wide range of scenes such as street views, dashboard cameras, real estate literature introductions, and drone imagery. As most of these scenes are captured using fisheye lenses with large distortion, omnidirectional cameras are not commonly used for three-dimensional shape measurement or image processing. Although various conventional methods have addressed these limitations by applying perspective projection transformation to 360° images, this transformation increases the processing time. A fundamental challenge in image recognition is the detection of straight and parallel lines. Accordingly, I propose a method to detect these lines directly from 360° images without using perspective projection transformation and then estimate the axial direction and camera attitude of the detected parallel lines. Through experiments, I compared the proposed method with conventional line detection using perspective projection and demonstrated a short processing time of the proposed method and accurate detection of parallel lines. The processing times of the proposed method were approximately 10 and 30 ms per frame for cameras with 2K and 4K resolutions, respectively. In addition, the detection accuracy of parallel lines was 87% when excluding environment factors. The attitude estimation errors were approximately 11° and 5° for 2K and 4K resolutions, respectively.
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