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calibration procedure. Since the height error is known in correspondence with each calibration point, it is possible to 
determine the value of the estimate of p which guarantees the required accuracy. 
À statistical analysis of the measurement errors has been performed in order to certify the system. In the case of 
maximum contrast of the gratings, the system accuracy is equal to 0.158 mm with a precision of 0.2 mm. In the case of 
half contrast, the system accuracy is equal to 0.218 mm, with a precision equal to 0.217 mm. 
4. INTEGRATION OF THE TWO SUBSYSTEMS 
In order to merge DHI profile measurements with whole field profile measurements, a suitable procedure has been 
implemented to measure the relative position and orientation of the coordinate frame of the two systems. The 
procedure is based on the following steps: 
a) the DHI profilometer positions its Z axis perpendicular to the whole field profilometer reference plane (therefore 
parallel to the Z axis of the whole field profilometer): the procedure is automatic and based on triangulation; 
b) the DHI spot is directed towards a series of points on the reference plane: for each point the spot is located by the 
whole field profilometer camera. A simple elaboration of the data gives the relative shifts as well as the relative 
orientations of the X and Y axes of the two coordinate systems; 
c) the absolute distance of the reference plane is measured by the DHI system and stored as the zero quote: the 
following Z quotes will be measured with respect to this zero. 
5. REFERENCES 
Biancardi, L., Carrato, S., Ramponi, G., Sansoni, G., 1994. Whole field optical profilometry: application of nonlinear 
processing algorithms to the enhancement of low-contrast images. In: Proc. SPIE Videometrics Ill, 2350, pp. 336-342. 
Biancardi, L., Sansoni, G., Docchio, F., 1995. Adaptive whole field profilometry: a study of the systematic errors. In 
press on IEEE Transactions on Instrumentation and measurement. 
Docchio, F., Perini, U., Tiziani, H., 1994. A combined distance and surface profile measurement system for industrial 
applications: a European Project. Meas. Sci. Tech., 5, pp. 807-815. 
Gelmini, E., Minoni, U., Docchio, F., 1994. Tunable, double-wavelength heterodyne detection interferometer for 
absolute-distance measurements. Opt. Lett., 19, pp. 213-215. 
Déandliker, R., Thalmann, R., Prongué, D., 1988. Two-wavelength laser interferometry using superheterodyne 
detection. Opt. Lett., 13, pp. 339-341. 
Sansoni, G., Docchio, F., Minoni, U., Biancardi, L., 1993. Adaptive profilometry for industrial applications. In Laser 
Applications to Mechanical Industry, S. Martellucci and A. N. Chester Eds., Kluwer Academic Publishers, pp. 351-365. 
Sansoni, G., Biancardi, L., Docchio, F., Minoni, U., 1994a. Comparative analysis of low-pass filters for the 
demodulation of projected gratings in 3-D adaptive profilometry. IEEE Trans. Instrum. Meas., 43, pp. 50-55. 
Sansoni, G., Biancardi, L., Minoni, U., Docchio, F., 1994b. A novel, adaptive system for 3-D optical profilometry using a 
liquid crystal light projector. IEEE Trans. Instrum. Meas., 43, pp. 558-566. 
Sódnik. Z., Fischer. E., Ittner. T., Tiziani. H., 1991. Two-wavelength double heterodyne interferometry using a matched 
grating technique. Appl. Opt., 30, pp. 3139-3144. 
Tang S., Hung, Y.Y., 1990. Fast profilometer for the automatic measurement of 3-D object shapes. Appl. Opt., 29, pp. 
3012-3018. 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop “From Pixels to Sequences’, Zurich, March 22-24 1995