1. A method for determining dimensional accuracy of a three dimensional (3-D) object having a complex shaped surface S in comparison to a reference image of the 3-D object, comprising: obtaining scanned image data of the object and apportioning a surface of the scanned image into a plurality of regions; obtaining reference image data of the object and apportioning a surface of the reference image into a plurality of regions, wherein each of the plurality of reference image regions corresponds to one of the plurality of scanned image regions; comparing corresponding regions of the scanned image and the reference image and identifying a closest matching region based upon the comparing; determining a virtual datum based on the closest matching region and a critical feature; aligning the scanned image data and the reference image data using the virtual datum; and comparing the scanned image and the reference image.