The directions for aerial surveys, drawn up by Prof. Alfredo 
Paroli and adopted (by a ministerial decree of the 11th of July 1952) 
by the General Direction of the Italian Cadastre as a rule for cadastral 
aerial surveys in Italy, have ratified testing criteria based mostly on 
the principles of the above mentioned method. 
But in the Chapter XII some rules of testing, by which must 
be certified in a definitive way the conformity and accuracy of the map 
and of the other cadastral works, they make reference (par. 82), for the 
planimetry, to the same rules used for maps from classic methods, 
while for the altimetry (par. 83 and foll.) the testing is carried out by 
means of tacheometric traverses. 
All this shows that there is no easy way to reach the rational and 
complete photogrammetric self-testing. 
2. Tolerances specifications. 
The precision and the characteristics of a photogrammetric map 
are established by a tolerance statement generally constituted by a list 
of tolerated differences between the co-ordinates of a point by the map 
and the same co-ordinates obtained in a different way. Frequently speci- 
fications fix also a law of distribution of the percentage of the devia- 
tions with different magnitudes in order to assure that the errors, owing 
to the differences themselves, are of accidental and not of systematic 
nature. 
Generally the specifications must consider too the possibility of an 
error made in the second research of the co-ordinates of the tested point. 
For instance the instructions for the aerial surveys of the Italian 
Cadastre, fixing the altimetric tolerances (pag. 90) for 1/2000 scale 
maps, between a longitudinal profile of the ground directly produced 
from the map, and the same profile surveyed by means of altimetric 
traverse - either the surveyed profiles hae been obtained by an ordinary 
tacheometer and vertical stadia or by means of spirit level or precision 
tacheometer and horizontal stadia - establish respectively, for slopes 
smaller than 25%, differences of 2 m or of 1,80 m and for slopes greater 
than 25% (being i the slope of the ground) respectively : 
La = V 3,75 p 9,7ts&^ i or t, « | 3 + 7,5tg"i 
gt : 
The error made in the research of the testing co-ordinates sometimes 
could become preponderant.