7 
sed 
phs 
s 
s 
the 
hese 
s in 
ee 
the 
horizon line (h-^, h2, I13, I14, h^) in corresponding horizon photos are stereo- 
scopically measured using the floating mark (Fig. 7). The differences of these 
parallax readings, R^ - h^, R2 - h.2, R3 - I13, R4 - h^, R3 - h^, express the 
displacement of the horizon line in the measured horizon photo relative to the 
horizon line in the corresponding reference horizon photo. 
The expression 
(Rf - h^) + (R2 - h2> + (R3 - I13) 4- (R4 - I14) + (R5 - h 5 ) 
5 
is the vertical displacement of the horizon line of the measured photo relative 
to the corresponding reference horizon photo. 
The equation, 
CX. = ( R 1 " ^l) + ( r 2 " ^2) + ( R 3 “ ^3) + (R4 - h4) 4- (R5 - h5) n 
5 f 
nd 
o 
one 
r 
es 
the 
where f is the focal distance of the horizon camera, gives the relative 
difference in inclination of the aerial camera between the 
measured photo and the reference photo. 
Since horizon photos are taken in four perpendicular directions, 
the tip and tilt can be determined twice: the tip C^) from the forward and the 
aft photos; and the tilt (to) , from the left and the right photos. 
The differential tip and tilt can also be determined in a different 
manner from the differential inclination of the horizon line. In this case, the 
left or the right photo is used for the determination of ^ , and the forward or 
aft photo for the determination of CO .