The two eyepieces are mounted on a revolving plate (48), rotating
up to 180°, so as to allow their transposition needed for aerial trian
gulation. The Amici prism may be made to rotate in order to
cancel stereoscopy for the measurement of vertical parallaxes.
In order to facilitate the latter measurement a glass plate (65 see
fig. 3 a) with plane parallel faces is interposed between the photo
graph and the end section of the optical system.
Such plate (mounted through a universal joint) might be tilted in
various ways around an axis parallel to Bx by means of a micro
metrie screw affording measurement of parallaxes to an accuracy
of the order of 2 microns.
This plate is the one used, as we shall see later, when making
automatic correction for any residual projection errors, small
as they may be.
Distortion correction (see fig. 3b) is performed by the well-known
Santoni cam-device which is fitted on spherical joint (30). Such
device automatically varies the principal distance (f) of the perspec
tive, when the angle formed between the line of sight (as set on
each occasion) and the axis of the perspective itself varies.
Recent improvements on the tools used in working the cams made
it possible for distortions to be corrected to less than 2 microns
on the entire field (including super wide-angles).
The cams very moderate in price can be easily designed and pro
perly worked to correct also the errors due to the earth curvature
and to the refraction.
Carriages X, Y, Z of coordinatograph. Base components
(Bx, By, Bz) (see fig. 1 and 4).
The base of the apparatus in welded tubular steel, parallelepided
in shape, is supported by three levelling screws.
The base supports three cylindrical guides of which two horizon
tal side ones (long ones) and one (short) central guide on which a
quadrangular carriage (14) may rest or slide. We refer to it as « first
carriage ».
It is actioned by a screw (placed in the vicinity of the central guide)
controlled, through the appropriate transmission system, by the
