Research On Atmospheric Refraction In Fish-eye Star-map Positioning

The implementation of traditional celestial navigation and positioning have changed with the utilizing of fisheye cameras.Although fisheye camera has the advantage of large field of view,the distortion and the influence of the atmospheric refraction to positioning based on star-maps captured by fisheye cameras will be enhanced and the impact of the atmospheric refraction cannot be ignored.This paper has carried on systematic research on this problem and accomplished the precision calibration of the fisheye camera based on the automatic measurement system for dome point and the algorithm for star point extraction,which reduced the implication of the atmospheric refraction to the camera calibration and got the camera parameters not been effected by atmospheric refraction.Then reduced the implication of the atmospheric refraction to positioning by using the parameters not been effected by atmospheric refraction and the compensation algorithm to the atmospheric refraction.The main contents and innovations of this paper are as follows:1.The automatic measuring system was established for stars on the simulated dome.As an indoor calibration platform for fish-eye cameras,it has a direct impact on the accuracy of the star-table and the camera's parameters.This article greatly improves the measurement efficiency by transforming the traditional passive measurement to automatic measurement based on the image acquisition and communication module of Leica TS 50 I video total station,and it changes the measurement mode to double-face measurement at the same time,which effectively eliminates the instrument and 2C error,etc.and it also helps improving the measurement accuracy.2.An extraction matching method was proposed for star points prediction by using camera parameters and star table.The method replaces the blind extraction and matching according to predicting the image coordinates of the star point by using the camera parameters and the star table and then performs partial star point extraction,which reduces the number of noise points and simplifies the procedures of calculation and improves the efficiency.3.A method was proposed to the indoor camera calibration without the influence of atmospheric refraction by using the automatic measurement system and the result of star point prediction algorithm which can avoid the influence of atmospheric refraction on camera parameters.4.The accuracy of several atmospheric refraction correction algorithms and the influence of meteorological factors on atmospheric refraction were compared and analyzed.And the positioning precision of different atmospheric refraction correction models was contrasted by using the height method according to experiment.5.The paper studies and improves the residual compensation method for atmospheric refraction.The influence of atmospheric refraction cannot be eliminated completely only by atmospheric refraction model through experimental analysis.This problem can be solved by using residual compensation.However,it's not suitable for fisheyes as the use of a constant atmospheric refraction correction residue for atmospheric refraction compensation when positioning by fisheye star-maps because of its large field of view and the large scale of the zenith distance covered by the star points.The paper proposes the linear compensation and trigonometric function compensation based on the above.Experiments show that this method can improve the positioning accuracy effectively,making the final positioning latitude and longitude error better than 1?.