501 
Ps î 
Fig. 6. 
fh 
II 
n + 1 
— b • dp • n • 
(8) 
2 fh n 
- bn (n + 1) 
(9) 
Applicating this correction vve should get correct heights in an ideal 
case. 
b z for each photograph should correspond to true statoscop values. 
The correction for the curvature of the earth in photogrammetry 
The following account is intended to give a simple derivation of the 
influence of the curvature of the earth in photogrammetric height 
measurements and the possibility and result of a correction for this 
effect. For a more detailed study of this problem reference is made to 
Ohlin [7]. 
With minor approximations the following relations are valid. 
According to Fig. 5 the distance between a point P on the earth and 
a tangent plane is 
dh = — 
(10) 
In an arbitrary point in 
the tangent point we have 
dh rr 
a coordinate system (x, y) with origin in 
X 2 + y 2 
2R 
/ 
(11)