Structural analysis of clastic dikes using Structure from Motion - Multi-View Stereo: a case-study in the Paraná Basin, southeastern Brazil

ABSTRACT: This work presents the development of a three-dimensional (3D) model of an outcrop of the Corumbataí Formation (Permian, Paraná Basin, Brazil) using Structure from Motion - Multi-View Stereo (SfM-MVS) technique in order to provide a structural analysis of clastic dikes cutting through siltstone layers. While traditional photogrammetry requires the user to input a series of parameters related to the camera orientation and its characteristics (such as focal distance), in SfM-MVS the scene geometry, camera position and orientations are automatically determined by a bundle adjustment, an iterative procedure based on a set of overlapping images. It is considered a low-cost technique in terms of hardware and software, also being able to provide point density and accuracy on par to the ones obtained withTerrestrial Laser Scanning. The results acquired on this research have good agreement with previous works, yielding a NNW main orientation for the dikes measured in the field and on the 3D model. The development of this work showed that SfM-MVS use and practice on geosciences still needs more studies on the optimization of the involved parameters (such as camera orientation, image overlap and angle of illumination), which, when accomplished, will result in less processing time and more accurate models.

摘要：本研究构建了巴西巴拉那盆地（Paraná Basin）二叠纪Corumbataí组（Corumbataí Formation）露头的三维（3D）模型，采用运动恢复结构-多视图立体匹配（Structure from Motion - Multi-View Stereo，SfM-MVS）技术，旨在对切割粉砂岩层的碎屑岩脉开展结构分析。传统摄影测量需用户输入一系列与相机姿态及其特性（如焦距）相关的参数，而SfM-MVS技术可通过光束法平差——一种基于多幅重叠影像的迭代处理流程——自动确定场景几何、相机位置与姿态。该技术在软硬件层面均属于低成本方案，其生成的点云密度与精度可媲美地面激光扫描（Terrestrial Laser Scanning）所得结果。本研究获得的结果与前人工作吻合度较高，野外与三维模型中测得的岩脉主方位均为北北西向。本研究表明，当前SfM-MVS技术在地球科学领域的应用仍需针对相关参数（如相机姿态、影像重叠率与光照角度）开展更多优化研究，完成此类优化将进一步缩短处理时长并提升模型精度。