Ph 
Py 
  
Fig. 4. Horizontal and vertical parallaxes caused by the lens distortion of a pair 
of pencils of rays within the stereo-area. 
— — 
where |P,| and |p,| represent the lengths of the vectors respectively. 
This relation defines the "theoretical 0-position". 
Now we assume that the relative orientation changes this position by 
the effect of a tilt ¢. Still considering the pictures as approximately ver- 
tical we get a “disturbed 0-position" 
— > = 
— — 
P—0, =p, ~p, pp, 
> 
uas uer: (3) 
In this expression we have 
A A A A 
Bm bb. potum, 
Or 
^. A A A 
p,= + Pp, PP, 
e e 
The vector p, can be converted into an altitude in relation to the refe- 
— 
rence plane in the ordinary way [14]). In the same manner p, will give 
9 
the change of altitude caused by the tilt e. The effect of ç concerning the 
vertical parallaxes will result in a subtraction of the vector P. from 
o 
the vector P. owing to the rotary direction of e. 
But the instrument operator is not aware of this "theoretical O- 
position”. He only observes the existing p -parallaxes in the selected 
orientation points of the principal verticals, and his aim will be to re- 
duce the parallaxes to such a small amount as he can. These amounts 
— 
we call the residual vertical parallaxes A p,. Thus we get 
_— — > 
— -— i — A 
A P, = P, — P, = (Ip, + Ip, ) DU entre (4) 
13