1. A method of reconstructing a surface of an object; the object being represented by a 2-dimensional grid of measurements, where for each grid point the measurements include corresponding information on a first slope of the surface in a first direction and a second slope of the surface in a different second direction; the method including: in a processor, selecting a 2-dimensional part of the grid over which an accurate reconstruction may be carried out, fitting a corresponding part of the surface to the measurements of all grid points in the selected part, thereby significantly reducing the effect of a localized measurement error to the area of the selected 2-dimensional part, and providing a representation of at least the reconstructed surface part, where the fitting for each grid point of the selected part is based on both the corresponding first and second slope information.