PROCESSES AUTOMATION IN 3D SPELEOLOGICAL MAPPING FROM PHOTOGRAMMETRIC MODELS OF UNDERGROUND CAVITIES IN MINAS GERAIS, BRAZIL.

Abstract

Speleological maps have been produced in Brazil since the mid-nineteenth century by manual processes by topographic surveys and sketches. In recent decades, technological innovations such as electronic distance meters and integration with cave surveying softwares have allowed the preparation of digital maps, still using manual procedures. Besides laser scans, short-distance photogrammetric surveys have been used to generate 3D models of cavities. They assisting the construction of speleological maps from automated procedures that allow the extraction of metric information accurately, contributing to the reduction of errors and time. This process allows us to obtain the limits of a cavity in classic views such as floor plan, longitudinal profiles and cross-sections and other less common ones, such as longitudinal and transversal vertical projections. In addition, it permits extracting contour lines and other features of interest that are vectorized from mosaics of orthophotos of the floor, walls and ceiling of the cavity. 3D photogrammetric models of caves allow the calculation of speleometric variables, including volume, that are difficult to obtain by the conventional topographic method. These can be integrated with topographic surface models with high-resolution images, contributing to the visualization and analysis of the landscape and its site characteristics. The surveys carried out in the Sete Salões Cave and Veloso Gold Mine demonstrated that the generated models present geometry very close to the real one, and can be performed in natural or even artificial cavities, such as historical gold mines. Following the proposed workflow aimed at generating 3D speleological maps, they are an alternative to traditional topographic surveys, and can even be applied to three-dimensional modeling generated from point clouds by laser scans.