The aim of the work is to estimate the error of the ortho rectification of aerial images obtained by unmanned aerial vehicle for a mountain site in the village Shidnytsya with the help of additional grid of points obtained by GNSS-survey. The task is to analyse the difference between the heights of the points obtained using two methods: using the map of heights from the UAV survey and using data of GNSS-survey and then to estimate the difference between the real coordinates of the ground control points with their coordinates on the orthophoto plan. The method. It is proposed to use the method of ortho rectification of aerial images obtained by UAV on mountainous terrain for determination of the real value of height error. A local test site with size approximately 70x60 meters was created on the hill in the village Shidnytsya, The site is part of terrain covered by a general aerial survey of the village. On this site an additional GNSS-survey was implemented and a grid of points with measured coordinates was generated with step one meter. Processing of the obtained ortho image height map based on the data of the aerial survey of the entire Shidnytsya and the results of GNSS-survey was realized in the software of ArcGIS. Layer of points of the local test site was overlaid on the aerial image and then this data were compared with the coordinates of the same points obtained from the map of heights. Results. Comparing the height values of 87 points on the test site to the height values of the same points obtained from the map of heights created on the basis of aerial survey implemented by unmanned aerial vehicle, it was determined that the height values of the points are not very different. The root mean square error is 0.39 m. Scientific novelty. The method of comparing the values of terrain point heights obtained using different technologies for determination of the value of the error of ortho rectification of aerial images obtained by UAV on mountainous local site near the village Shidnytsya is proposed. Practical significance. The obtained results of error values of aerial images ortho rectification show that ortho rectification of aerial images of some mountainous areas obtained using the UAV is in the zone of tolerance
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