Lens distortion practically presents in a real optical imaging system causing nonuniform geometric distortion in the images and\r\ngives rise to additional errors in the vision measurement. In this paper, a planar-dimensions vision measurement method is\r\nproposed by improving camera calibration, in which the lens distortion is corrected on the pixel plane of image.The method can\r\nbe divided into three steps: firstly, the feature points, only in the small central region of the image, are used to get a more accurate\r\nperspective projection model; secondly, rather than defining a uniformmodel, the smoothing spline function is used to describe the\r\nlens distortion in the measurement region of image, and two correction functions can be obtained by fitting two deviation surfaces;\r\nfinally, ameasurementmethod for planar dimensions is proposed, in which accurate magnification factor of imaging system can be\r\nobtained by using the correction functions. The effectiveness of the method is demonstrated by applying the proposed method to\r\nthe test of measuring shaft diameter. Experimental data prove that the accurate planar-dimensions measurements can be performed\r\nusing the proposed method even if images are deformed by lens distortion.
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