The accuracy of aerial data is directly related to the spatial resolution of the input imagery. The high resolution images from UAV can compete with traditional aerial mapping solutions that bank on highly accurate alignment and positioning sensors on board. The advancement of computing practices resulted in vigorous and fully automatic production practices and coupled with high-end computing machines and viewing mechanisms will deal with positional inaccuracies and imagery orientation information which are characteristically challenging with customary techniques. Processing of UAV images has its own challenges. MAS used to receive post-processed UAV images along with inertial measurement unit (IMU) and ground control points (GCP) as input. Aerial Triangulation is the first step performed. During this stage GCP and Actual Check Point (ACP) reports have been generated. This is an iterative step until we get the desired accuracy. The following will explain in brief some of the critical steps in the processing of UAV data:
- The software examines for matching points by analyzing all images. The software used here an improved version of the binary descriptors, which are very powerful to match image points quickly and accurately.
- Those matching points as well as estimated values of the image position and orientation provided by the UAV autopilot are used in a bundle block adjustment to reconstruct the exact position and orientation of the camera for every acquired image.
- Based on this restitution the matching points are corroborated and their 3D coordinates calculated. A proper projection system is selected based on the requirements, and also GPS measurements from the UAV autopilot during the flight.
- 3D points are interpolated to form aTriangulated Irregular Network (TIN) in order to obtain a DEM. The spatial resolution of the TIN is moderated as per the need of 3D model requirements.
- This DEM is used to project every image pixel and to calculate the geo-referenced ortho-mosaic. The orthoimages will be cleared of positional and terrain displacement inaccuracies.