1. A computing device, comprising: at least one processor; a storage system; and one or more programs stored in the storage system and being executable by the at least one processor, the one or more programs comprising: an obtaining module obtains a boundary line graph from the storage system, wherein the boundary line graph comprises a plurality of endpoints, and each endpoint is labeled with a label character; an adding module adds a segment line between two adjacent endpoints of the boundary line graph, if the two adjacent endpoints are not connected using the segment line; a calculation module calculates the number of intersection points among the segment lines; a removing module searches for the intersection points which are not the endpoints, removes the segment lines of the endpoints corresponding to the intersection points, if the number of the intersection points is not equal to the number of the endpoints; the calculation module further calculates a boundary line vector, which is vertical to the boundary line graph; and a changing module changes label characters of the endpoints to be arranged in a predetermined order, if an order of the label characters of the endpoints is not a predetermined order according to the boundary line vector.