GEOMETRIC ACCURACY ASSESSMENT OF UAS-BASED ORTHOPHOTOS AND GNSS OBSERVATIONS USING RTK MODE

Abstract

This paper attempts to research and investigate geometric quality of an Unmanned Aerial Orthophoto from DJI Phantom 4 Pro for map generation and compilation despite the fact that a fewer number of control points were used and this was then compared with same points as observed from a Hi Target V30 GNSS Receiver in Real Time Kinematic (RTK) mode. Two important criteria are pivotal to Geometric quality assessment of an Aerial photograph; Geometric accuracy and Object-definition property while this research focused on the geometric accuracy as compared to another method of terrestrial data acquisition using GNSS. In remote sensing and photogrammetric operations, the geometric quality of the imagery purely depends on the relation between pixel size and the map scale including contrast information, atmospheric condition, the sun elevation, the printing technology and the screen resolution. The Unmanned Aircraft System (UAS) deliverables which include the Orthophoto and the Digital Surface Model (DSM) among other deliverables like Digital Elevation Model, Point Cloud etc. shows that UAS (Phantom 4 Pro) can be used for compilation of large scale maps in partly accessible or inaccessible areas according to the map accuracy analysis of the National Standard for Spatial Data Accuracy (NSSDA). The horizontal accuracy of 3.207m (RMSE: 1.85m) and vertical accuracy of 0.884m (RMSE: 0.45m) were obtained and also compared with the corresponding results from the RTK observations in DGNSS and falls within the allowable misclosure, hence, suitable for Cadastral mapping procedures and compilation.