tioned according both to survey and to data processing requi- 
rements. 
In the surveying of models of medium dimensions, in the 
industrial field, one problem is difficult to solve: the mar- 
king of control points for an absolute orientation. 
These points must be: 
a) fixed with a level of precision of about 0.1 mm; 
b) identifiable photographically; 
c) conveniently arranged 
with regard to the model. 
It is without doubt difficult (and often impossible) to 
place these points on every car model studied: it is more use 
ful to set up an independent system that is valid for all the 
models to be studied. 
As an experiment we have tried both methods in order to 
discover the advantages and disadvantages of each method and 
to see what precisions can be obtained, 
As for as the first method is concerned, there follows a 
description of the procedure adopted; as regards the second 
method, we have constructed a facility using wires, similar 
to a prototype already used experimentally in the surveying 
of one of the bronze horses on the Basilica of St. Mark in Ve 
nice (see publ. 3). 
Four wires of harmonic steel were used, supported on a 
special ly-built framework. Three brass pegs were fixed onto 
each wire. The framework was fitted with three micro-metric 
screws that allowed it to be placed horizontally to a trestle 
on which it was put. 
As regards the experiments carried out in the laboratory 
of Photogrammetry in the Turin Polytecnic, this framework was 
placed on a trestle of metal tubes about 2 metres from the 
ground, The wires were set in pre-arranged holes, and their 
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