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: determining a non critical feature of the 3-D object; determining a critical feature of the 3-D object; selecting a preliminary datum based upon at least one non critical feature; determining a virtual datum based upon the preliminary datum and the critical feature; obtaining a scanned image of the 3-D object; aligning the scanned image and the reference image using the virtual datum; and comparing the scanned image and the reference image.