Patent ID: 8260024

Claim:
A method for determining a shape of a surface of a test object, comprising: providing a measurement system including: a pattern including a plurality of first elements dispose about a central axis and defining an aperture containing the central axis, the first elements including a plurality of common elements having a common form and a reference element having a reference form that is different than the common form, the first elements further including a first reference element and a second reference element each having a same reference form that is different than the common form; a detector array; a processor; and an optical system disposed between the pattern and the detector array along an optical path; disposing a test object at a predetermined location relative to the measurement system; reflecting light from the plurality of first elements off a surface of a test object; passing the reflected light through the aperture and forming an image of the first elements that is received by the detector array; determining via the processor a shape of the surface of the test object using data from the image of the first elements; identifying a plurality of element images on the detector array, each of the element images corresponding to the first reference element, the second reference element, or one of the plurality of common elements of the first elements; and determining the shape of the surface of the test object based on calculated locations of the element images on the detector array.