Comparative Study of Digital Terrain Models (DTM) Using DRTK 2 Drone and GNSS Methods

Abstract

The spatial representation of the Earth’s surface, as well as the surfaces of other geometric objects, involves a series of representation models. Digital Terrain Models (DTMs) represent the natural surface of the land without the structures or vegetation that cover it. Today, photogrammetry, with the advent of drone technology, has advanced working methods in precision topography and allows for much more efficient DTMs. However, there are several sources of errors in positioning due to instrumental, procedural, and environmental factors that arise during the process. The objective of this study is to validate the relevance of new drone technology in its application to topography, particularly in the production of DTMs. For this purpose, a DJI Phantom 4 Pro RTK drone was used to acquire 392 images in an area with difficult topography (8 ha), supported by 12 previously established ground control points (GCPs) whose altitudes were determined by a precision direct leveling operation. The processing was carried out using two photogrammetric processing software (Pix4D and Agisoft Metashape) to compare their performance on DTM accuracy. Then, GNSS surveys in real-time mode (RTK) were carried out to produce three-dimensional models to be used for comparison and validation purposes. The vertical error of the three digital terrain models (DTMs) was evaluated by comparing them with direct leveling campaign data on the ground. We found that the result from the GNSS processing method achieved the best performance in terms of absolute error evaluation. Between the results provided by the two software programs, Agisoft offers slightly better results than those obtained with Pix4D.