Direct Geo-Referencing is a new technique in photogrammetry, especially in the aerial photogrammetry. Unlike the Aerial Triangulation "AT", this method does not require Ground Control Points "GCPs", to process aerial photographs into desired ground coordinates systems. Compared with the old method, this method has four main advantages: faster field work, faster data processing, simple workflow and less cost. Generally, direct georeferencing using two systems, Global Navigational Satellite Systems "GNSS" and Inertial Navigational System "INS". GNSS recording the camera coordinates "X, Y, Z", and INS recording the camera orientation angles "w, φ, k" at the time of exposure. These parameters merged and are provided to each photograph in the processing stage. The current paper investigates the using GNSS system for providing the linear exterior orientation "EO" parameters "X, Y, Z" by two techniques, real time kinematic "RTK" and virtual reference system "VRS". The accuracy of the applied method is tested on topographic survey project in Switzerland. The surveyed data of the specified project were collected by amateur digital camera Canon 18.2 MP, 182 captured images from approximately 85 m flight height, 18 Ground Check Point "GCP" determined by static GNSS. Horizontal accuracy is 0.029 m for VRS case, 0.034 m for RTK case and vertical accuracy is 0.026 m for VRS case, 0.029 for RTK case.

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surveying. The UAVs are equipped with a camera to collect data without any physical contact with the objects. So, the UAV platform can overfly accessible, inaccessible, and dangerous wide areas with high-resolution data in a short time and with little effort, (Mesas-Carrascosa et al., 2016).

advantages, photogrammetry based on the UAV platform has become a popular technique in mapping topographic applications. Capturing imagery by a camera installed in UAV has importance in cartographic (