A method obtains an original point-cloud of the object, filters discrete points from the original point-cloud, determines a first sub-point-cloud and a second sub-point-cloud from the filtered point-cloud, and creates an updated point-cloud of the object based on the first sub-point-cloud and the second sub-point-cloud, determines points to be fitted from the updated point-cloud. The method further fits a figure according to the determined points, determines a reference figure according to the fitted figure, determines a first point from the first sub-point-cloud and a second point from the second-point-cloud, calculates a gap width and a gap height of the updated point-cloud according to the first determined point, the second determined point, and the reference figure, and displays the gap width and the gap height on a display device.