3 
the various requirements of theory and practice, provide in turn results 
consistent with the map tolerances required. 
Among these solutions a particular mention should be made of the 
numerical process of approximate planimetric adjustment, studied on 
the occasion of some aerophotogrammetric surveys at the scale of 
1:2000 which we shall describe later on and which appears to be based 
essentially on the transformation by interpolation of the coordinates 
of the points observed, from the instrumental system to the terrestrial 
topographic system. This process, which should simplify and automatise 
the adjustment of the single strips undergoing analogical aerial triangu 
lation, was in fact successfully applied also to the adjustment of 
small blocks of strips in large-scale mapping. 
Starting from the presupposition that the planimetric deformations 
produced during instrumental bridging result to be the uniform function 
the x, y coordinates of the points considered — an ideal circumstance 
to which the result of a bridging may be approximated when operating 
so as to avoid any possible cause of accidental error [4] — the method 
described is most effectively applied if we use, during the bridging 
itself, the numbers of spot elevations available, determined on the field 
by means of spirit leveling. 
These points may in fact result particularly precious for the alti- 
metrical settlement of the various models of the strip, during the 
operations to transfer the absolute orientation derived from the first 
stereogram, providing advantage of a final reduction of the manifold 
and not controllable causes of error. 
2. After the instrumental bridging of a strip is completed, the main 
problem to be faced is that of transforming the coordinates of the 
points observed from the machine system to the topographic system, 
used to draw up the map. As is known, this transformation requires 
the previous reduction of the various machine coordinates, read in 
the different models of the strip, to a sigle system of reference, which 
generally would be the one of the model forming the first stereogram. 
Under the above mentioned conditions, verifying a parallelism 
between the z and Z axes of the two orthogonal terns, instrumental