Highly Accurate Attitude Estimation via Horizon Detection

AbstractAttitude pitch and roll angle estimation from visual information is necessary for GPS-free navigation of airborne vehicles. We propose a highly accurate method to estimate the attitude by horizon detection in fisheye images. A Canny edge detector and a probabilistic Hough voting scheme are used to compute an approximate attitude and the corresponding horizon line in the image. Horizon edge pixels are extracted in a band close to the approximate horizon line. The attitude estimates are refined through registration of the extracted edge pixels with the geometrical horizon from a digital elevation map DEM, in our case the SRTM3 database, extracted at a given approximate position. The proposed method has been evaluated using 1629 images from a flight trial with flight altitudes up to 600ï źm in an area with ground elevations ranging from sea level up to 500ï źm. Compared with the ground truth from a filtered inertial measurement unit IMU/GPS solution, the standard deviation for the pitch and roll angle errors obtained with 30 Mpixel images are 0.04ï ź and 0.05ï ź, respectively, with mean errors smaller than 0.02ï ź. To achieve the high-accuracy attitude estimates, the ray refraction in the earth's atmosphere has been taken into account. The attitude errors obtained on real images are less or equal to those achieved on synthetic images for previous methods with DEM refinement, and the errors are about one order of magnitude smaller than for any previous vision-based method without DEM refinement.