Crack is a major defect of buildings. Digital image methods are often used to detect cracks. But incorrect or un-unique results may be inverted with an inappropriate algorithm. An image processing way is presented to obtain the sole width value. Meanwhile, the crack with several branches can be measured. In the processing, the crack skeleton is first calculated. Then each of the points on the skeleton is served as a center of a group of circles, one by one. The radius of the circles is increased step by step. The iterations will not stop until any point in the circle goes out of the crack. Thus the last circle in the iteration is served as an incircle of the crack. The diameter of the incircle is a crack width in a given skeleton point. The maximal and average width of the crack will be calculated after all the incircles with all the skeleton point are traversed. The experimental results show the proposed method can extract the width of cracks in a complex context.

This paper studies three-dimensional laser scanning system of human body, and make adjustments according to the world coordinate error correction based on the point cloud obtained. This paper also analyzed the cause and characteristics of three-dimensional laser scanning system’s world coordinates error, and established the world coordinate correction model on the condition that vertical column coordinate error is not included in the calibration plane and the error is minimum relative to other highly cross-section. With a standard rectangular timber as the scan objects, correction factor is fitted and the effectiveness of this method is proved through experiments in which point cloud’s world coordinate error is significantly reduced.