This paper reports an experiment conducted to evaluate correction methods of chromatic aberrations in images acquired by a nonmetric digital camera. The chromatic aberration correction methods evaluated in the experiment are classified into two kinds. One is the method to correct image coordinates by using camera calibration results of color-separated images. The other is the method based on the assumption that the magnitude of chromatic aberrations can be expressed by a function of a radial distance from the center of an image frame. The former is classified further into five types according to the difference of orientation parameters common to all colors. The latter is classified further into three types according to the order of the correction function. We adopt a linear function, a quadratic function and a cubic function of the radial distance as a correction function. We utilize a set of 16 convergent images shooting a white sheet with 10 by 10 black filled circles to carry out camera calibration and estimate unknown coefficients in the correction function by means of least squares adjustment. We evaluate the chromatic aberration correction methods by using a normal image shooting a white sheet with 14 by 10 black filled circles. From the experiment results, we conclude that the method based on the assumption that the magnitude of chromatic aberrations can be expressed by a cubic function of the radial distance is the best method of the evaluated methods, and would be able to correct chromatic aberrations satisfactorily enough in many cases.

Commission I, ICWG I/VKEY WORDS: Measurement, Non-Metric, Camera, Calibration, Orientation, Application, Engineering, Experiment ABSTRACT:This paper reports an experiment conducted in order to investigate the feasibility of the deformation measurement of a large-scale solar power plant on reclaimed land by using images acquired by a non-metric digital camera on board a micro unmanned aerial vehicle (UAV). It is required that a root mean squares of errors (RMSE) in height measurement should be less than 26 mm that is 1/3 of the critical limit of deformation of 78 mm off the plane of a solar panel. Images utilized in the experiment have been obtained by an Olympus PEN E-P2 digital camera on board a Microdrones md4-1000 quadrocopter. The planned forward and side overlap ratios of vertical image acquisition have been 60% and 60% respectively. The planned flying height of the UAV has been 20 m above the ground level and the ground resolution of an image is approximately 5.0 mm by 5.0 mm. 8 control points around the experiment area are utilized for orientation. Measurement results are evaluated by the space coordinates of 220 check points which are corner points of 55 solar panels selected from 1768 solar panels in the experiment area. Two teams engage in the experiment. One carries out orientation and measurement by using 171 images following the procedure of conventional aerial photogrammetry, and the other executes those by using 126 images in the manner of close range photogrammetry. The former fails to satisfy the required accuracy, while the RMSE in height measurement by the latter is 8.7 mm that satisfies the required accuracy. From the experiment results, we conclude that the deformation measurement of a large-scale solar power plant on reclaimed land by using images acquired by a nonmetric digital camera on board a micro UAV would be feasible if points utilized in orientation and measurement have a sufficient number of bundles in good geometry and self-calibration in orientation is carried out.

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