期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2004
卷号：XXXV Part B3
页码：1-6
出版社：Copernicus Publications
摘要：Airborne videos are gaining increasing importance. Video cameras are taking huge amounts of measurements for low costs. Their low weight and low requirement for energy makes them particularly attractive for small airborne carriers with low payload. Such carriers are discussed for military as well as for civil applications, e.g. traffic-surveillance. Often video cameras are used for documentation and reference in connection with other sensor systems. In addition to panchromatic or ordinary colour videos, nowadays also cameras operating in the thermal spectral domain gain attention. For the utilization of any stream of measurements taken from a moving platform the pose of the sensor in orientation and position has to be constantly determined. For airborne platforms often GPS and INS are used to acquire this information. However, the video stream itself provides also possibilities to estimate pose parameters. In this contribution we restrict our investigation to almost flat scenes but we allow oblique views both forward looking and side looking. The optical flow of the scene fixed structure on the world plane is estimated by a planar projective homography. This requires at least four point or line correspondences that can be traced over an appropriate number of frames. If the focal length is not changed and the camera has not been rotated, the proper transform will be restricted to a central collineation with five degrees of freedom. Two of these - giving the vertex or epipole - can be inferred directly from image correspondences. The remaining three are then estimated from the homography by solving a homogenous linear system. They give the axis or horizon, from which we obtain the rotational part of the pose, and a scale parameter for the speed to height ratio. Common level keeping flight manoeuvres where the epipole is close to the horizon lead to elations. Other manoeuvres - like e.g. landing - lead to homologies. The rotation-free calculations will also be appropriate if the camera rotation is known from another sensor. If the rotation between the frames is unknown the homography will be decomposed into a central collineation and an orthogonal rotation matrix. The five degrees of freedom of the collineation and the three degrees of freedom of the orthogonal rotation matrix sum up to eight, which is exactly the same number of degrees of freedom that a planar homography has. There is a set of analytic solutions to this equation system, of which the correct solution can be picked by heuristic considerations. We investigate the propagation of measurement errors through these calculations. Examples for such estimations are shown for thermal videos. Long focal lengths are unfavourable. The rotation-free decomposition gives more stability compared to the decomposition with rotation
关键词：Geometry; Vision; Estimation; Navigation; Orientation; Infrared; Aerial; Video
