Summary:

On the base of geodetic, photogrammetric or radio observations of the sheet objects its position, dimensions and shape are determined. Approximation of mathematical model for the surface, used as a reference for estimation of geometric state of the object is based on the space co-ordinates of points representing the sheet of the object. In practice, the model parameter values are determined without consideration of accuracy of these co-ordinates. However, the covariance matrix for co-ordinates of observed points constitutes a base to estimate accuracy of determined parameters and its functions. In this paper an algorithm enabling es-timation of accuracy for the estimated parameters of the surface is presented. In addition, a measure of fitting of mathematical model to the observed geometric state of the sheet is determined. This parameter can be used to decide on adequacy of a medel. A method of estimation of the unit variance estimator reflecting effect of measurement errors only is also described.