A NEW PROPOSAL FOR THE GENERAL AND OPTIMAL CONFORMAL UPDATING 
OF A CADASTRAL DIGITAL MAP: THE ITALIAN CASE 
Alberto Beinat and Fabio Crosilla 
Dept. of Georesources and Territory, University of Udine, Via Cotonificio 114, I-33100 Udine, Italy 
beinat@dgt.uniud.it, crosilla@dgt.uniud.it 
KEY WORD: Cartography, Adjustment, Integration, Algorithms, GIS, Procrustes analysis. 
ABSTRACT: Referring to the current state of the Italian cadastral map, the paper describes an innovative analytical method to 
perform the general adjustment of the fiducial point network, and the optimal conformal adaptation of new surveyed cadastral parcels 
into an already existing digital map. Working on the surveyors' data files containing the mutual distance values between couples of 
fiducial points, the proposed procedure reciprocally fits, in the least squares sense, the various and corresponding fiducial polygons, 
as elemental component parts of the general fiducial network, by way of similarity transformation adjustment models computed by 
Generalised Procrustes algorithms. The proposed method furnishes more accurate results than those obtained by the conventional 
least squares adjustment of the individual distances measured between fiducial points; furthermore it satisfies and advantageously 
preserves the geometrical shape of the original surveys. In addition, the preservation of the original shape allows also the conformal 
mosaicking of the new surveyed cadastral entities with those ones obtained by the digitisation of the original maps. 
Finally, some numerical examples show the capabilities of the method proposed. In the first example, a network of fiducial points has 
been simulated, and the original data have been modified in such a way to reproduce different error situations. The analysis of the 
results has been carried out in a systematic manner. It has furnished the comparison of the obtainable levels of precision and accuracy 
by applying the two alternative methods: the Procrustes algorithms for the global and simultaneous adjustment of the fiducial point 
polygons, and a conventional approach based on the adjustment of the single polygon sides. In the second experiment, the Procrustes 
procedure has been applied to the general adjustment of a relevant number of real and surveyed fiducial polygons, located in the 
north-west side of Udine municipality. The realisation of this experiment is given to the cooperation between the University of Udine 
and the Udine “Agenzia del Territorio“ of the Italian Cadastre Administration. 
1. INTRODUCTION and extremely expensive to ex novo survey the entire national 
network of the cadastral fiducial points, constituted by four 
The earliest numerical archives of the Italian Cadastre millions points, and to neglect, at the same time, more than 
Administration have been established, since the eighty's, by ^ thirty millions distance measurements between couples of 
digitisation of the existing cadastral maps, previously drawn on fiducial points, carried out in the last years. For this reason it 
paper sheets or polyester films, generally at 1:1000 and 1:2000 becomes reasonable to propose and to experiment new 
scale. This fact pointed out, among the others, the problem of analytical techniques to globally adjust all the available direct 
the accuracy of the resulting parcel vertex coordinates, that and indirect measurements acquired between the fiducial points, 
showed, in some circumstances, error positions of several and constrain the corresponding geometry to a limited number 
metres. To perform a sound update of the digital cadastral of control points, surveyed by GPS, in order to improve the 
mapping, the Italian "Agenzia del Territorio", started at that acuracy of the fiducial point network, and to define the 
time a virtuous process based first, on the use of new coordinates of all the points into a unique common datum. 
topographical measurements carried out by various professional The second relevant aspect is the updating problem solution of 
surveyors, and second, on the application of specific rules the cadastral digital mapping, consisting in the optimal insertion 
requiring, for instance, to refer the new cadastral surveys to at of the new geometrical entities, more precise and reliable than 
least three fiducial points materialised on the terrain, whose the previously digitised ones, into the original numerical map. 
original coordinate values were assigned, for the largest part of The analytical procedure proposed in this paper, based on the 
them, by the digitisation process. In this way, for the zones of Generalised Procrustes techniques, can be adopted with success, 
recent urbanisation, a wide series of direct or indirect distance first for the rigorous adjustment of the fiducial point network, 
measurements between the fiducial points have been collected second for the optimal mosaicking of the various cadastral 
in the last years. By these data, the Italian Cadastre parcels, and third for the global and simultaneous adjustment- 
Administration, after considering a limited number of fiducial update of both the fiducial point network and the cadastral 
points as fixed, has locally determined the new positions of the parcels. 
other not fixed fiducial points, updating their corresponding In the first case, by applying to each polygon (or triangle) of 
coordinate values. All this according to specific significance fiducial points surveyed in the field independent translations, 
criteria of the points taken into account and of the declared rotations, and scale variations, it is possible to obtain the so- 
precision of the executed measurements. called mean shape network of the fiducial points satisfying, in 
However, the adopted procedure presents some disadvantages: the absence of gross errors, the original shape of each 
the coordinate values of the not fixed fiducial points vary in composing fiducial polygon. In the second hypothesis, the same 
time, and the homogenisation principle of the point coordinates analytical procedure can be properly applied for the update of 
might fail for a wide area, since the correction of the coordinate the digital mapping by a cartographic mosaiking of the various 
values acts locally and it does not rigorously propagate to the parcels. This means, from the operational point of view, a first 
entire zone of interest. Although recent cadastral plans foresee splitting of all the digital parcels of the original cadastral map, 
the creation of new first and second order fiducial networks by and their subsequent recomposition with the insertion of the 
GPS measurements, in the authors’ opinion it is not proposable 
30 
new O 
reliabil 
algoritl 
whole : 
Finally 
interde 
vertexe 
cartogr 
rigorou 
optima 
from th 
This la 
point c 
benefit: 
betwee 
cartogr 
2. TH 
Every t 
digital 
corresp 
and upl 
a speci 
"Pregec 
As outl 
the poii 
the par 
frame 1 
triangle 
comple 
to surve 
  
  
  
Figure 
From t 
reciproc 
points, : 
log then 
used to 
simplifi 
connect 
Al thi 
represer 
first ma 
rigorous 
The fun 
aims at 
(since t