The analysis of planetary satellites or asteroids ground based observations is quite similar. Our first goal was to improve the astrometric reduction for digitized photographic plates in case of too few reference stars and to propose solutions. We here present astrometric techniques used for old observations of the Galilean satellites made with the 26-inch refractor of USNO in Washington DC from 1967 to 1998 (Pascu, 1977, 1979, 1994). We present some solutions that may be applied to asteroids or any small solar system bodies observations. In fact, we were able to determine an observational error and we discuss the expected improvements necessary in the frame of the GAIA FUN SSO program. A real application in the frame of the Gaia program deals with the new analysis of old photographic plate observations.