Patent ID: 8447561

Claim:
A shape measurement method of combining plural sets of partial measurement data representing respective shapes of a plurality of partial surface regions of a workpiece to obtain an overall surface shape of the workpiece, using a shape measuring machine comprising a measuring unit and a processing unit, the method comprising: a step performed by the measuring unit of collecting the plural sets of partial measurement data from the plurality of partial surface regions of the workpiece; a step performed by the processing unit of isolating a specific frequency component from the partial measurement data; a step performed by the processing unit of transforming coordinates of the plural sets of partial measurement data to obtain plural sets of coordinate-transformed partial measurement data, using coordinate transformation parameters for each of the plural sets of partial measurement data, after the specific frequency component is isolated; a step performed by the processing unit of defining an approximated error shape which represents the overall surface shape of the workpiece and which is common to the plural sets of partial measurement data; a step performed by the processing unit of defining a reference shape including the approximated error shape and a design shape, using shape parameters; a step performed by the processing unit of computing differential shapes between each of the plural sets of coordinate-transformed partial measurement data and the reference shape and optimizing both the coordinate transformation parameters and the shape parameters so as to make an evaluation value defined from the differential shapes approach a predetermined value; a step performed by the processing unit of adding back the isolated frequency component to the partial measurement data after both the coordinate transformation parameters and the shape parameters are optimized; and a step performed by the processing unit of connecting the plural sets of coordinate-transformed partial measurement data, using both the optimized coordinate transformation parameters and the optimized shape parameters.