Evaluation of the light line displacement location for object shape detection

Abstract

The ability for detecting the location of the displacement of a projected light line with subpixel resolution is examined. This evaluation is carried out for measuring a three-dimensional object shape. The technique for measuring the object shape is based on the light line projection. To determine the height data, displacement of the light line is measured on a reference point and on the object surface. This line displacement is measured by approximating the line intensity to a continuous function by the least-squares method, the Gaussian approximation and the Bezier curves method. The light line position is defined by calculating a maximum from this continuous function. To evaluate these three methods it is necessary to know the best accuracy of the experimental results. To achieve this, the results extracted by these methods are compared with a contact method. This contact method is made with a coordinate-measuring machine. The rms error is calculated using data from these three methods and the data from the contact method to carry out this evaluation. Height data are obtained with great accuracy from the method, which has a better rms value. The time necessary for processing a light line using each of these three methods is also presented. In addition to this information, a correlation coefficient is presented giving the deviation of each function generated by these methods. This line projection technique has a great potential because a very simple experimental set-up is used which is inexpensive. This evaluation is tested with complicated objects and its experimental results are presented.