Orthoprejector, the’ Jena Topocart-Orthophot-Orograph, étc.) as well as 
to equipment in which the profiling is done automatically, using image 
correlators and associated control units (such as the Wild B8-Ste aL, 
the UNAMACE, etc.) : 
   
  
It is rec contour lines constructed from dropped lines, or 
from dropp > segments, cannot be as accurate as contour lines 
stereoplott sad in the conventional way. 
It is common knowledge that the latter, when produced on precision 
plotters or on good topographie S, have standard height errors 
x 
of 0.20 to 08.257 of the flying 
operator is given the task to raise 
mark during profiling so that it 
When, however, the human 
lower his travelling floating 
in contact with the ground, 
its ath 
      
  
   
   
he will have additional height-set errors of the er of 0.3 ro 
0.42 of the flyin eight (Ref. 1966, Visser Hobbie 1971) 
As for equipme 
Situation 
the Wild 
automatic, correlator-guided prof 
T 
ing, the 
seem to be much better. t 
xtensive paraitre nts with 
in the Institut Geographique N 
Ref.: Duche have led to the conclusion ti 
dropped line > to construct contours, a 
be chosen that is double rhe 
the contours j 
usine the 
interval should 
interval which would > been used when 
stereoplotted in the souvestéonat way. 
F4 0 
Q 
— 
z 
  
Moreover, the height information that is recorded in the form of dropped 
lines, or dropped line segments, is incomplete. .There is no height 
information in between the proi. les, which are separated by distances 
5 
« 
d. 
4 
equal to the slit-width used. The contours derived from the dropped 
line data ther efore do not re present the,actual physiography of the 
  
pM 
m 
e 
tn 
terrain and us include interpolation errors. Theoretical considera- 
tions E EE ed 1970) show that these additional errors are negli- 
gible only when the profile-interval is not larger than the horizontal 
distance between the contour lines (this distance being equal to the 
vertical contour interval times the cotangent of the terrain slope). 
It may thus, in general, be stated that contours derived from dropped 
line data will have height errors (0.4 to 0.5Z of the flying height) 
that are tvice as large as the errors in conventionally stereoplotted 
contours (0.20 to O. 25% of the flying height). The "C-factors' of 
these two "systems" are thus 650 and 1300 respectively. 
The lower accuracy of the dropped line system may not be too serious 
in the case of medium or small scale orthophotomaps, where relatively 
large contour intervals are used and where, moreover, the following 
statement (Ref.: Doyle 1971) applies: "in a photo map, a larger con- 
tour interval may be satisfactory (as compared to line maps), since the 
detailed character of the terrain is usually apparent from the photo- 
graphic image anyway, and more contours will obscure more photographic 
detail.' 
For large-scale orthophoto maps, however, say, at scales 1:1,000 to 
1:10,000, a relatively high height accuracy is required. For tne basic 
1:5,000 scale map of Western Germany, for instance, obtaining height 
information from dropped lines is not considered satisfactory at all 
(Ref.: Krauss 1971). The height information is obtained instead by 
-3- 
conventiona 
orthophoto p 
from special 
south Africa 
1971) "the c 
dropped line 
Apart from t 
present .anot 
proximate co 
be cartograp 
portray the 
a well train 
as for stere 
Krauss 1971) 
À practical 
ventional st 
example it i 
duced on the 
graph, and t 
the photomap 
Using the dr 
flying heigh 
contours in 
1300, the fl; 
Production e 
for 100 mode 
orthophot. 
conversio 
for 25 model: 
orthophot« 
conventioi 
From this we 
aerial photo; 
significantl 
In this conte 
new orthophoi 
A8, the new 1 
Hobrough Gest 
taneous prod 
Several inst: 
ment and of 1 
and longer c«