Cadastral cartography, born after unification of Italy in 1870, is an important source of large scale geographic
information.
Cadastral maps represent the result of the largest scale survey of on the whole national territory. Because of
their large scale, their creation is extremely expensive and the updating of the cadastre claim considerable
funds from the state budgets. That’s why the coordinate system, the geodetic basis of a cadastral work, is
rarely changed.
Even if Gauss-Boaga grid system based on ROMA40 datum was introduced and applied at some smaller
parts of the country, the cartographic coordinates manly used in the cadastral maps are based on CassiniSoldner
projection and cadastral datum Bessel-Genova; Bessel_Monte Mario and Bessel Castanea delle
Furie.
In the Cassini-Soldner projection, the whole Italian territory is subdivided in 31 major ("grandi origini") and
more than 800 local ("piccole origini") cadastral systems.
Nowadays, it is fundamental the implementation of a fast and free procedure for the updating of cadastral
maps from Italian cadastral datum to modern WGS84.
The two main goals of this paper are: the identification of a suitable set of points with coordinates known in
both datums and the computation of Abridging Molodensky parameters from Cassini-Soldner cadastral
datum to WGS84. The test area selected is the district of Rome called “Città metropolitana di Roma
Capitale” .
The data set of points suitable for the least-square estimation is extracted from the information available on
the website www.globogis.it/fiduciali.it.
The "globogis" database includes a selection of trigonometric points, with coordinates expressed in the
WGS84 datum, and a selection of cadastral points ("punti fiduciali") with coordinates expressed in the
Bessel-Genova 1902 datum. The whole database is analysed in order to provide the correct association
between cadastral and trigonometric points.
Known the dataset of points, the Abridging Molodensky parameters are estimated with a least square
principle using a specific package developed by Prof. Timar.
The estimated parameters are implemented and tested in the open source software QGIS. The accuracy of
Abridging Molodensky parameters is tested using an independent set of point with respect to the estimation
points
