ISPRS-Annals ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences ISPRS-Annals ISPRS Ann. Photogramm. Remote Sens. Spatial Inf. Sci. 2194-9050 Copernicus Publications Göttingen, Germany 10.5194/isprs-annals-X-4-W1-2022-143-2023 COMPARISON OF UAV IMAGE SPATIAL RESOLUTION BASED ON THE SIEMENS STAR TARGET Fakhri S. A. 1 Motayyeb S. 2 Saadatseresht M. 2 Zakeri H. 3 Mousavi V. 4 Dept. of Geomatic Engineering, Faculty of Civil Engineering and Transportation, University of Isfahan, Isfahan, Iran Dept. of Photogrammetry and Remote Sensing, School of Surveying and Geospatial Engineering, University College of Engineering, University of Tehran, Tehran, Iran Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran Geomatics Engineering Faculty, K.N. Toosi University of Technology, Tehran, Iran 13 01 2023 X-4/W1-2022 143 150 Copyright: © 2023 S. A. Fakhri et al. 2023 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://isprs-annals.copernicus.org/articles/X-4-W1-2022/143/2023/isprs-annals-X-4-W1-2022-143-2023.html The full text article is available as a PDF file from https://isprs-annals.copernicus.org/articles/X-4-W1-2022/143/2023/isprs-annals-X-4-W1-2022-143-2023.pdf

In recent years, as the use of Unmanned Aerial Vehicle (UAV) imaging systems has increased, the photogrammetry community has conducted extensive research on the unique advantages of these systems. The UAVs are considered as one of the most important platforms for photogrammetry applications from various urban and non-urban areas at different scales. In UAV photogrammetry projects the spatial resolution of the images must be determined prior to the imaging stage. The spatial resolution of the images is a commonly-used criterion for detecting the smallest distance between two adjacent separable objects in the images. Numerous methods have been developed to precisely evaluate the spatial resolution of images. In this study, the Siemens star target, which is one of the most commonly used artificial targets for analysing spatial resolution was studied. The objective of this paper is to evaluate and compare the reduction of spatial resolution coefficient using the Siemens star target in images captured by UAVs. To this end, a method for automatically detecting the radius of the circle of ambiguity and calculating spatial resolution in UAV images has been developed. According to the findings of this study, the initial step in creating the Siemens star target, in terms of size and the number of acceptable arms, is dependent on the flying altitude of the UAV and the level of image blur. In addition, the reduction in spatial resolution of images captured by various UAVs varies, and its coefficient must be calculated for each project.