1. A method for measuring relative positions of a plurality of semiconductor device layers, comprising: selecting one or more patterns for each semiconductor device layer; obtaining one or more critical dimension scanning electron microscope (CD-SEM) images of said selected patterns; and calculating a relative pattern position between each said semiconductor device layer in vector form based on said obtained CD-SEM images, wherein each said semiconductor device layer includes one or more patterns, and wherein said one or more selected patterns are selected based on line symmetry or point symmetry of said patterns within at least one said semiconductor device layer.