1. A computing device, comprising: at least one processor; and a storage device that stores one or more programs, which when executed by the at least one processor, cause the at least one processor to: process images of a position device for a computerized numerical control (CNC) machine to obtain contour points of the position device; generate a point cloud according to the contour points of the position device; select a contour point from the point cloud; calculate a distance between the contour point selected from the point cloud and each unselected contour point in a predetermined area corresponding to the contour point; delete the contour point from the point cloud upon the condition that the distance corresponding to each of the selected contour points exceeds a predetermined threshold; and calculate an average coordinate of contour points remaining in the point cloud and confirm the average coordinate as a coordinate of a gravity point of the position device.