Drone survey of an embankment dam to detect surface changes

Abstract

A point cloud is a set of three-dimensional coordinates, to which color (that of the object's surface) can be added. It's a simple way to reproduce this object (which could be a dam, a building, a breakwater, a street, a room) on the computer. The point cloud can be obtained by laser scanner survey, photogrammetric survey and, in the case of small objects, also by 3D scanning. The coordinates resulting from laser scanners and photogrammetric surveys are generally obtained with less accuracy than those obtained by classical methods developed within the scope of geodesy and surveying (topography). For this reason, the use of point clouds (and the 3D models created from these) in dams to detect changes, for example for safety control studies, is more suitable to embankment dams as these are works where there is a requirement for slightly lower accuracy of results, on the order of few centimetres. Despite being less precise coordination methods, the laser scanner and photogrammetric methods have a very important advantage in earthworks as they cover the entire surface with a cloud with a high density of points. A localized problem can be easily detected if it has an expression on the surface of the work. As part of a study aimed at obtaining better knowledge of some details of an embankment dam situated in Portugal, two aerial photogrammetric surveys were carried out, approximately one year apart, with a drone. From these surveys point clouds and 3D models of the dam's surface were created. The communication presents various aspects of the surveys as well as the clouds and models generated.