Fig. 1. Principle of the absolute measurement method based on oblique incidence.

Fig. 2. Retrieval algorithms for absolute surface measurement.

Fig. 3. Relative interpolation error PV due to the oblique incidence angle for different flatnesses of L.

Fig. 4. Residual error (RMS) as a function of rotation angle.

Fig. 5. Repeatability error of PV as a function of the measurement times at different control errors for the rotation angle.

Fig. 6. Experimental setup for the absolute measurement.

Fig. 7. Surface form measurement results with three different methods: (a) oblique incidence method, (b) N-rotation method, and (c) relative measurement method.

Fig. 8. Gradient of the surface form measurement results with three different methods: (a) oblique incidence method, (b) N-rotation method, and (c) relative measurement method.

Fig. 9. Mid-spatial frequency error of the surface form measurement results with three different methods: (a) oblique incidence method, (b) N-rotation method, and (c) relative measurement method.