On the measure of land subsidence throughout DEM and orthomosaics using GPS and UAV

Today, topography is an essential part for the construction of civil works in Mexico and in the world, obtaining it has become a complicated task due to the large areas to be built, the difficult access that puts the integrity of individuals at risk; and the high requirement of personnel for the tasks. Currently, photogrammetry using unmanned aerial vehicles (UAV) has been potentiated due to the infinity of uses, autonomy and little demand for resources, to carry out tasks in short times. Furthermore, the topography was, until some years ago, quasi-static, however due to the alteration generated by human activities it has been transformed into a dynamic activity. This work presents the procedures to carry out a topographic survey in the Querétaro valley, in an area called “El Ensueño”, it has had a subsidence fault for years, and has been in constant movement, causing considerable damage to infrastructure. . The present study reveals for the first time an orthomosaic and a Digital Elevation Model (DEM) of the study site, for a survey with UAV it is necessary to use Ground Control Points (GCP), in order to correct the DEM by orthorectification of the images obtained during the flight by means of UAV. The results obtained show a total error in centimeters of 3.33 and image pixels in 0.311, both in the X, Y and Z space, which represent an acceptable error considering that the latter must be less than 0.6 pixels, so Therefore, the alignment of the images and measurement by GPS were performed correctly during the processing. Furthermore, the Digital Terrain Model (DTM) shows dramatic differences between one side and the other of the fault zone, which may indicate that this is a perfect tool to distinguish particular affected areas with a quick and more accurate method