LADYBUG3 CAMERA CALIBRATION

摘要

The applications of photogrammetry such as aerial triangulation, 3D modeling, and automatic texture mapping need precise camera internal geometry in order to obtain high precision results. Ladybug3 equipped with 6 short focal length fish-eye cameras, which can acquire 720 degrees panoramic image and is useful for augmented reality applications. The field of view (FOV) of each lens is about 95 degrees by 77 degrees. Thus, their lens distortion is serious and the way to calibrate their interior orientation parameters is critical for photogrammetry purposes. Therefore, this research proposes two types of indoor calibration field to solve these problems using single camera calibration and multiple camera calibration. A rotatable calibration field contains 112 pillars with Australis© coded target is designed. The basic idea of such calibration field is to acquire high convergent imaging geometry with lots of redundant image measurements by means of automatic code target recognition. The purpose of the second calibration field is to calibrate both the interior orientation parameters and relative orientation parameters between the six cameras. A 3D cube, with 4 meters in length, 3 meters in width and 2.5 meters in height is used, where 118 Australis coded targets are fixed and spread uniformly to the ceiling, the floor, and all four walls. Since the Australis is capable of self-calibrating multiple cameras at the same time, the interior and exterior orientation parameters can be solved. Based on the exterior orientation parameters, the relative orientation parameters can be estimated. The accuracy of relative rotation angles is around 0.02 degrees and the accuracy of perspective center offset which between the referenced camera to the others is less than 1 mm. It is expected that the accuracy is precise enough for direct georeferencing applications using a land vehicle mobile mapping system.