Investigation of rock mass deformation through nap-of-the-object photogrammetry: a case study of Hongyun Golden Peak in Fanjing Mountain, China

Abstract

Traditional field investigation methods are inapplicable in some landslide cases where numerous dangerous rocks are distributed. Therefore, nap-of-the-object photogrammetry (NOOP) has been developed for such applications while meeting the demand for fine measurements. The new technology involves using UAVs to fly close to the object surface to obtain subcentimeter high-resolution images. Afterward, software is used to achieve a fine surface model of the target object. In this paper, a case study of the deformation characteristics of the high-steep rock mass of Hongyun Golden Peak of Fanjing Mountain in Guizhou Province, China, is conducted. Through preliminary oblique photogrammetry, which involves data processing, NOOP route planning, and fine NOOP, a realistic 3D surface model of the Golden Peak of Fanjing Mountain is obtained. The resolution of the model could reach the millimeter level (2 mm). Detailed characteristics of the 3 groups of joints and 9 deep-large cracks are obtained from the rock structure investigation and statistical analysis of fissure deformation. NOOP can be used to acquire the elevation of the target object, thus compensating for the deficiencies of oblique photogrammetry. Additionally, it accurately reproduces the terrain and fine object structures. The results of this study can provide a reference for geological investigations involving monitoring high-steepness dangerous rocks.