obtained only by 
lable, Ope could, 
a System resemb. 
t cireles anq the 
the determination 
> Was accepted in 
strip of oblique 
lon of the line to 
oincidence in the 
of the groups of 
€, a Straight ]ine, 
nt of the oblique 
5 projected to the 
question and the 
is the projection 
gular geocentric 
efined coordinate 
lindrical surface. 
hrough the nadir 
ane 7. A straight 
reen | and m can 
(1) 
]titude above the 
3 
The value of the terms in parentheses is in practice very close to 1. 
The Z-coordinate of a point is composed of three elements: earth curvature, effect of 
| mospheric refraction and the topography of terrain. We can write 
Z —Z,T Z, t Z,, where 
X2 
Are $E 
+494 (h?— X?) 
Gs wna ED 
X2 
Z, = +e (1+ 57 +) 
In this set of formulae 
h = flight altitude, in meters; 
e = elevation of the point above the cylindrical 
surface; 
Log h = Brigg’s logarithm of % in meters. 
It should be mentioned here, that the units may be easily changed in the case of Z, 
nd Z,. On the contrary, in the case of Z, careful attention should be paid to the Jogarith- 
| nie tion involved in the formula. 
The formulae given above allow the computation of the Y-deviations from line L 
| Sce the equation of this line is known, the corresponding deviations from a str aight line 
uy be established. As a matter of fact, the curvature of line I is in most practical cases 
»small, that it can be ignored. 
So far a distortion free lens is assumed. The straight line in an oblique photograph 
in practice rather centrally located. This means, that the Y component of the distortion 
!sonly a small fraction of the real magnitude of radial distortion. Using calibration data 
if the oblique camera the distortion Y components can be determined. The effect of dis- 
ition on the ground coordinates is then computed from differentiation of the coordinate (0 
wnsformation formulae relating the oblique photograph and the ground system: 
| h sin®.h.y 
La (f cos 6 — x’ sin &) gu tfe cos ® — x’ sin $)? da (2) 
  
The meaning of dif- 
went symbols can be 
‘en from figure 2. 
Another method to 
lansfer the effect of 
lisfortion to the terrain 
5 based on the principle 
jt projective grid. Sup- 
je that the effect of 
iffortion is known in the 
‘train, and two straight 
Ines, parallel to the X- 
jus are placed through 
le distorted and un- 
Iktorted points. Assum- 
  
  
  
115 à plane terrain, the 
fou 
{ i 
| | 
| 
a 
| 
i 
1 
ne ———