Recovery of cadastral boundaries with GNSS equipment

Abstract

The purpose of this work is to propose a new redefinition of cadastral boundaries using GNSS equipment and cadastral maps. These maps are the ‘original’ maps of the Italian Land Cadastre, the first cartographic support built directly from measures carried out by technicians during implantation of the Italian land cadastre. They are called ‘originali di impianto’ – ‘originals of implantation’ or ‘implant maps’. As such, these maps are valuable and are kept with great care. Recently, the Italian cadastre has carried out an accurate digitisation of these maps in a raster format at a high resolution. In this work, the authors propose the use of these digital maps for the recovery of cadastral boundary. The original cadastral map, one of the primary sources relied upon in defining legal boundaries, generally uses the Bessel ellipsoid localised in Genova and the Cassini-Soldner projection; the GNSS equipment, on the other hand, uses the geocentric ellipsoid with global or continental realisations. After an RTK positioning, the receivers usually provide the cartographic coordinates in a Gauss projection. However, our study deals with the problem of using different projections and reference systems within the limits of a map. In this context, the transition between systems and projections can be made through a conformal transformation with deformations slighter than graphical errors in the map. The difficulty of finding identifiable points in both reference systems is partially solved through a new way of carrying out the redefinition of boundaries by exploiting geometric information.