Research On Fish-Eye Camera Stellar Calibration Technology

Analyzing the research status and development trends of fish-eye cameras calibration athome and abroad, according to the currently problems in fish-eye cameras calibration, thisdissertation proposes using stellar method to calibrating fish-eye cameras. In this dissertation, theprinciple of stellar calibration method is analyzed, and the calibration flow is presented, and allthe key technologies in calibration are analyzed and tested, which include star images getting,star points extracting, center coordinates calculating and star image identification. The bundleadjustment analytic formulae and DLT formulae of photogrammetry are derivated based on theprojective models of fish-eye cameras.4calibration models are presented. The calibratingexperiments are made using survey data, and the calibration accuracy is up to100’’, which isequivalent to the actual international best result. When the effectual calibration field of view isless than40°, the calibration accuracy of this paper is higher than the actual international bestresult. The matter of effectual calibration field of view is first presented in the world, and thevalue of it is presented in every calibration experiment. The effectual calibration field of view inthis paper’s experiment is more than140°, and the number of observation data is more than470,which are better than the actual international experiments. The experimentes of the extensibilityof effectual calibration field of view of different calibration modeles are made, and theexperiment resultes results and the advantages and disadvantages and the applicability of the4models are analyzed.The main works and contributions are summarized as follows:(1) The advantages and disadvantages of stellar camera calibration method are analyzed.The preponderance of stellar method in calibrating fish-eye cameras is discussed. The principleof stellar camera calibration method is studied, and the observation coordinate and model ofstellar camera calibration method are analyzed, and the calibration flow and key technologies arepresented.(2) A fish-eye camera which could image in180°space is established using the improvedNikon10.5mm fish-eye lens and the Alta U9000. The FPN and other noise of U9000CCD aretested and analyzed. The transformation methods from U900016bits images to Windows8bitsimages are studied, and the UMP class for saving and reading16bits images is defined.(3) The exposure time of Alta U9000is tested accurately, and the results make the error ofthe exposure time calculating using program execute time less than0.2ms.(4) The extraction methods of star points in fish-eye star images are studied, and the visualcase searching method is presented to shorten calculating time. The global threshold algorithm based on gray histogram which workes well in fish-eye star images and the self-adaptingthreshold algorithm for single star are presented. The star point automatic detecting algorithm ispresented according to star points’ characters that are different background and differentbrightness.(5) The uniform model of centroid algorithm is summarized, according to different forms.The simulation method of star point images based on2D Gauss distribution is introduced, andfactores which can influence the precise of star point center algorithmes are presented. Thesimulation experimentes of star point center calculating errors using all the common algorithmesin different star point images. According to the resultes, the applicability of different algorithmfor different star point images is discussed.(6) The star image identification algorithmes in common use are introduced, and theadvantages and disadvantages and applicability of the algorithmes are analyzed. Themulti-triangle identification algorithm based on datum stares is presented, according tocharacteres of fish-eye star images. To avoid the matter of this method that the identification timeof the datum stares is long, the improved multi-triangle identification algorithm is presentedcombining this method and the starlike mappings pattern algorithm whose calculating time isvery short.(7) The collinear equationes are derivated based on equisolid projection and equidistanceprojection of fish-eye lenses, and according to these equationes, the bundle adjustment analyticformulae and DLT formulae of photogrammetry are derivated based on equisolid projection andequidistance projection of fish-eye lenses.(8) According to the character of fish-eye cameras that the radial distortion is the maindistortion, two fish-eye camera calibration modeles, the equisolid projection polynomial modeland the equisolid projection ten-parameter model based on the restriction of angle of halfcoverage. The calibration experimentes are made using the two modeles and observation data,and the experiment resultes are analyzed.(9) According to the analytical formula of photogrammetry in equisolid projection, theself-calibration adjustment model in equisolid projection is presented. The calibrationexperimentes are made using this model and observation data, and the experiment resultes areanalyzed and compared to that of common self-calibration adjustment model.(10) To calibrate the fish-eye cameraes whose projection modeles are unknown, thecalibration method based on projection surface fitting is presented which is independent ofprojection model. The calibration experimentes of fish-eye camera using equisolid projection aremade using this model and observation data, the experiment resultes are the same well to theequisolid projection polynomial model. (11) To the matter of effectual calibration field of view in calibrating fish-eye camera, theexperimentes of the extensibility of effectual calibration field of view of different calibrationmodeles are made, and the experiment resultes are analyzed. According to this resultes, theadvantages and disadvantages of the four fish-eye camera calibration modeles presented in thisdissertation are analyzed synthetically, and the applicability of different modeles are discussed.(12) The survey experimentes for an indoor minitype parabolic reflector antenna are madeusing the fish-eye camera, according to the total station’s survey data for the antenna. Thediscussion preparatory to application of fish-eye camera in measurement is made, and conclusionis educed that if the fish-eye camera used in measurement, when calibtating, all the field of viewwhich could used in measurement should have observation data.