A scanner obtains point-cloud data of adjoining parts of a product. A computing device reads two point-clouds from the point-cloud data, fits two or more lines according to the two point-clouds, selects two lines that have the same ascending direction from the two or more lines, and creates a two-dimensional coordinates system base on the two selected lines. The computing device determines a highest point in each of the two point-clouds based on distances from each point in either of the point-clouds to a corresponding selected line, and determines two nearest points in the two point-clouds. A difference between Y coordinates of the two highest points is determined as a gap-height of two adjoining parts of the product, and a difference between X coordinates of the two nearest points is determined as a gap-width between two adjoining parts.