12 
has been obtained both as regards the precision of the photo- 
grammetric method of surveying industrial models, and as re- 
gards the most appropriate system of control-points. 
For the photographic operations we refer the reader to 
Fig. 2, in which the position taken up by the three types of 
camera used is shown in a plan, in relation to the piece to be 
surveyed, 
For all the cameras the relationship p was equal to three. 
It is perhaps appropriate to note here that the sheet me 
tal model, with its panel support, was put in a vertical posi 
tion with all possible care; moreover, it was connected to the 
metal trestle that gave general support. 
Then the wire framework was positioned hear the model, in 
the way shown in both Fig, 2 end Fig, 3. We then moved on to 
the levelling of the apparatus itself using a spirit level 
with a degree of sensitivity of 10”. The wires and their re- 
spective weights were stretched out, and the vibration absor- 
bers were put in, 
Using the Wild NA2 level placed a few metres from the wi 
res, we proceeded to move the central pegs of the second, third 
and fourth wires to the same level as the central peg of the 
first wire, 
Frequent checks were made, before, during and after the 
photographs, to see that the whole apparatus remained in the de 
sired conditions, 
The cameras were placed in position at such a height from 
the ground so as to always have the main point of the photogram 
approximately at the same level as the middle pegs. 
As shown in Fig. 3, these, too, were placed 130 cm from 
the ground, taking into account first a the positions of the 
other pegs, and then the positioning of the piece to be surve 
yed, 
The photographs were of a normal type. 
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