XXIX International Symposium on Modern Technologies, Education and Professional Practice in Geodesy and Related Fields, İstanbul, Turkey, 5 - 06 November 2019, pp.55
Aerial or satellite imagery technologies have conventionally been used as a data source for geographic data collection, surveillance, mapping, and 3D modelling issues. However, over the past decade, unmanned aerial vehicle (UAV) low-altitude remote sensing technologies are widely used as an effective, fast and inexpensive tool for creating accurate orthophoto maps. The accuracy and precision of orthophoto generated by Structure from Motion (SfM) photogrammetry tool based on UAV photographs depends on many parameters including camera/image quality, flight plan, SfM algorithms and geo-referencing strategy. Taking into consideration the advantages and disadvantages of using ground control points in orthophoto production, a process based on resolution, point density, accuracy, time, expertise and costs is required. On the other hand, conventional geo-referencing based on ground control points provides high accurate positioning but the geometrical accuracy critically depends on the number and spatial distribution of the ground control points. However, direct geo-referencing of the UAV images by using the high accurate positioning ability of Network RTK and Single Base RTK methods may overcome these limitations. Therefore, the automated extraction of control points by the double frequency GNSS receivers can be eliminate the need for ground control points especially for emergency mapping applications. The main purpose of the study is the investigation of the accuracy of orthophoto production without ground control points for mapping applications. In the study, Single Base RTK and Network RTK methods based on GNSS techniques were used during AUAV's flight for direct geo-referencing. 13 ground control points were placed homogeneously at the test area for the validation of the orthophoto accuracy generated by direct geo-referencing. The ground control points were measured with Network RTK method. The images were collected using a UAV and professional camera, at a flight height of 40 m above the ground. Analysis has been carried out in order to reveal the effect of the direct geo-referencing by Single Base RTK and Network RTK positioning methods on orthophoto generation in terms of accuracy and precision.
Keywords: UAV; Orthophoto; GNSS; RTK