Analysis and Comparison of the Conventional Methods of Georeferencing of Aerial Photos

Aerial photos are the basis of many researches, both applied and executive works, related to the earth. Applications of aerial photos, especially for GIS-based analysis, aerial photo georeferencing, and/or geometric correction are essential. Various methods have been proposed for georeferencing. The aim of this study was to achieve a suitable simple method with a low cost and acceptable accuracy. For this purpose, conventional georeferencing methods, including first- to third-order polynominal transformtions, spline transformtion, projective transformtion, and orthorectification transformtion were used in ILWIS3.3 and ArcGIS10.7 for two areas (flat area of Shahrekord and rugged area of Chaleshtor). Errors of the different methods were analyzed based on minimum and maximum errors, Mean of Error (ME), standard division, and Root Mean Square Error (RMSE). The results showed that the errors of the varied methods had fewer changes for the flat compared to the rugged area. Yet, with the increasing relief of land surface, the errors increased sharply and showed a significant difference. Based on the results, the most accurate georeferencing method was orthorectification method (ME=35 and RMSE=38). However, considering the time and data required for the orthorectification method, the most suitable georeferencing method was identified as the spline method, which had acceptable accuracy, but not the problems of the orthorectification method, such as marginal information of the aerial photos and digital elevation models.