92 
Substituting this expression into (354) we find 
  
So S 6 S? 
/ — — — Ie 9 , : 5 2 
mem ss t (358) 
  
Now we want to determine h so that à, becomes as small as possible, 
finding the minimum of the expression 
6 S? : 
in = 132 359 
min ho? + 1322 (359) 
Applying the usual procedure we find 
d min 68? 
i e Mx +132 = 0 (360) 
The second derivative which always is positive indicates that a mini- 
mum exists. 
From (360) 
S y22 
h Zo 29 ô (361) 
For wide angle photographs and normal overlap we have 
3 
ó—— 
I 
Hence from (361) 
h I 0.35 S (362) 
Or 
S == 2.9 h 
Following these assumptions the stereo-radial method will have the 
smallest radial standard error in the middle of the strip when the flying 
altitude is about one third of the triangulation distance. 
From (357) and (362) we find 
n : 0