6 
PIERO BENCINI 
— the soil has a most varied aspect, as there are fairly large urban centres, 
agricultural land, forests, bush and bare land ; 
— the fact of being near Florence, where the Institute has its seat, would 
facilitate ground operations. 
The size of the area has been chosen in view of the foreseable size of blocks 
of strips for medium or large scale maps ; however, the procedures studied may 
be extended also to blocks of larger size, and the limits of such an extension may 
be the subject of special studies. For organization convenience the polygon has 
been limited by parallels 43°45' and 44 0 and by meridians i°i5' and i°37'3o" 
(west longitude from Rome M. Mario) comprising the area of 9 sections of the Map 
of Italy at the scale of 1/25000 (see annex 1). 
Within the polygon area, we had to determine about 300 control points, dis 
tributed as uniformly as possible, and suitably targeted. 
Aerophotogrammetric surveys had to be effected at two different flight heights, 
so as to get a series of photographs at the scale of about 1/20 000 and another 
one at the scale of about 1/30 000. The strips were to have an 80 % longitudinal 
overlap, so as to derive from each of them two independent strips with a 60 % 
overlap, and a side overlap of not less than 10 %. 
The flights were to take place by strips from east to west, or vice versa, and 
certain strips were to be effected also from north to south, or vice versa, at the 
end parts and in the middle of the polygon. 
3) - Ground operations. 
In February 1963 a meeting was held in Florence between the representatives 
of the Istituto Geografico Militare and those of the Photogrammetry Training 
and Study Centre of the Milan Politecnico, when the above mentioned rules were 
laid down. In particular it was decided that the determination of control points 
should take place according to the following phases : 
— set up a trigonometric basic net, to be adjusted in one single block, 
to serve as basis for later determinations ; 
— set up an adequate number of additional points, to be mostly determined 
by multiple forward intersection from the points of the basic net, to ensure an 
adequate density of known points from which to derive the determination of control 
points ; 
— set up 300 control points, determined by multiple inverse, direct or 
mixed intersection from the points of the basic and additional nets, with an average 
square error in each of the three coordinates not above i 30 cm. It was laid 
down that not more than 10 % of these points were to be on buildings, provided 
their form would guarantee an exact stereoscopic collimation, whilst the other 
ones were to be pegged out on the ground. It was further laid down that the points 
were to be materialized by means of a metal cap cemented onto the ground or the 
building, set in the centre of a flat circular spot of a diameter of 120 cm, painted