° photogram- 
sible number 
tant overlap 
height. 
erally recog- 
ny cases this 
lied even by 
he survey is 
"inciples. 
best method 
s Escadrilles 
| is standard 
their results 
le lap. 
ecause these 
te for aerial 
and to other 
pplying them 
ns in line. 
Zo is deter- 
4:25 
point of the 
ide lap 
scale. 
then deter- 
ed by means 
ltimeter and 
twenty me- 
ttoscope. The 
nces are sta- 
t land marks 
= photo size. 
te. 
2, by a value 
re 3). 
accuracy to 
thod is called 
R. navigation 
SURVEY NAVIGATION, CORTEN 63 
In case no sufficient num- 
ber of good landmarks is avail- 
able, the heading necessary to 
make the desired track can be 
determined using points of the 
previous flight line. The slant 
angle vy to these points can be 
expressed, measured and used 
to determine the heading angle 
a (figure 5). 
Precision turns are exe- 
cuted at the end of each flight 
line in order to arrive at the 
exact starting point for the 
next flight line. This can be 
achieved 
a. by manual piloting to a point 
chosen visually by means of 
pelorous visor according to 
angle f; 
  
Fig.4. Solar compass with photo-electric sensor and 
with servo to pilot’s heading display. Standard equip- 
ment in U.S.S.R. survey aircraft. 
b. according to I.G.N. (figure 6) by introducing the line spacing L, drift ó and speed V 
  
Rn 
into the computation to find the rate of turn and time of turn to be executed manually. 
A special slide rule is constructed. Figure 7. 
c. according to Brucklacher, using the same principles but flying compound turns con- 
sisting of segments at turn rates 1°, 2° or 3° per second by auto pilot;