钻孔图像展开与拼接方法研究

Research on unwrapping and stitching methods for borehole images

  • 摘要: 通过图像展开与拼接技术生成孔壁全景图及“虚拟岩心”是地质构造定量分析的基础,也是钻孔探查的迫切需求。针对现有钻孔图像展开与拼接方法存在的图像轮廓模糊、图像拼接不连续等问题,提出基于随机抽样一致性(RANSAC)算法的图像展开方法和基于加速鲁棒特征(SURF)+随机采样最大似然(MLESAC)算法的图像拼接方法。采用RANSAC算法对孔洞边缘数据进行圆拟合,获取钻孔中心及钻孔内径,从而确定有效环形图像区域;结合坐标变换算法和双线性插值法将有效环形区域并展开为矩形图像,可有效补偿成像探头抖动导致的几何畸变,实现钻孔图像的高精度展开。选用SURF算法快速提取相邻图像的特征点并进行粗匹配,在图像旋转和尺度变换下保持特征稳定性;再通过MLESAC算法对提取的特征点进行精准匹配,剔除误匹配点并筛选最佳匹配对,进而解算水平与垂直偏移参数,实现视频图像的全局高精度拼接。对比分析结果表明,相比于现有装置采用的图像展开与拼接方法,所提方法获得的全景孔壁图像连续无间断、细节分辨率高,拼接质量与视觉效果均大幅提升。

     

    Abstract: Generating panoramic borehole wall images and "virtual cores" through image unwrapping and stitching is the basis for quantitative analysis of geological structures and is also an urgent need in borehole investigation. To address the problems of blurred image contours and discontinuous stitching in existing borehole image unwrapping and stitching methods, an image unwrapping method based on the Random Sample Consensus (RANSAC) algorithm and an image stitching method based on the Speeded Up Robust Features (SURF) plus Maximum Likelihood Estimation Sample Consensus (MLESAC) algorithm were proposed. The RANSAC algorithm was used to perform circle fitting on borehole edge data to obtain the borehole center and borehole inner diameter, thereby determining the effective annular image region. By combining the coordinate transformation algorithm and bilinear interpolation method, the effective annular region was then unwrapped into a rectangular image, which effectively compensated for geometric distortion caused by probe jitter and achieved high-precision unwrapping of borehole images. The SURF algorithm was used to rapidly extract feature points of adjacent images and perform coarse matching while maintaining feature stability under image rotation and scale transformation. The MLESAC algorithm was then used to perform precise matching of the extracted feature points, remove mismatched points, and select the optimal matching pairs, thereby estimating horizontal and vertical offset parameters and achieving global high-precision stitching of video images. Comparative analysis results showed that, compared with the image unwrapping and stitching methods used in existing devices, the proposed method produced panoramic borehole wall images that were continuous and uninterrupted, with high-resolution detail, and significantly improved both stitching quality and visual quality.

     

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