line technique 
Figure 3 for 
oto contours 
1tal orthophoto 
be 0.3 °/oo 
In the pre- 
>s have demon- 
opline techniques. 
iformation de- 
aper are no 
the orthophoto 
little effect 
thophoto and 
ly improved 
jt. 1s. used. It 
e derived for 
feature may be 
5 in the recti- 
er are related 
iracy offered 
nciple the same 
  
as that of single orthophotos, but the stereo-orthophoto technique has 
the advantage that no discrepancies exist, due to imperfections in the 
orthophoto process, between the Stereocompiler plots and the orthophoto 
image. This is an important feature in the production of orthophoto 
maps where a good agreement between the orthophoto image and the 
plotted data is essential. 
Reproduction Methods 
Before starting on the reproduction of photomaps the article titled 
"The transfer of resolution in the production of orthophotos" (Ref.: 
Collins and Kelensky 1970) has to be mentioned as this is a good link 
between application and reproduction. In reproduction we have to 
guarantee that the utmost care must be taken to maintain the information 
given in the original aerial photo-negatives. As a matter of fact not 
only the reproduction techniques have to be as good as possible bu 
also the production of the orthophotos themselves has to be considered 
carefully. This is what Collins and Kelensky have done in their pro- 
found study on the transfer of resolution involved in the following 
steps (starting with the aerial negative): diapositive printing (by 
contact); orthophoto negative proipetton (optical type); orthophoto 
printing (by contact) 
The orthophoto projection was carried out on two instruments, the SFOM 
Orthophotographe and the Kelsh orthophotoscope, both using a Kelsh 
type projector for preparation of the orthophotographs. 
To study the loss of resolution in diapositive making of the aerial 
negatives a total 80 diapositives were produced on a Morse contact 
printer, a LogEtronic contact printer and a Wild projection printer. 
All diapositives were made on glass plates from two manufacturers, on 
two emulsion types. The conclusion reached was that the LogEtronic 
contact printer gave the best result, second and third were respectively 
the Morse contact printer and the Wild U3A. All however suffer a con- 
siderable loss in resolution. To improve results significantly the 
writers advise the use of strongly directional illumination in exposure 
and a more perfect contact between the negative and the positive plate. 
The research on different emulsions showed that the Kodak plates of 
contrast grade gave higher resolution than those of medium grade, but 
the difference was less than 5%. There was no significant difference 
between plates of different thicknesses or between Kodak or Ilford 
plates. It is remarkable that the greatest loss in resolution - about 
43% - is at the center of the photo. 
In the projection of the orthophoto negatives the SFOM and the Kelsh 
orthoprojectors showed almost identical results. Here there was also 
a loss of about 237 at the center of the field. 
The losses in final contact printing of the orthophotos were small. 
In conclusion the writers say that the great loss in diapositive print- 
ing from the original aerial negative is so significant in comparison 
with .the loss in the other steps of production that it is worthwhile 
considering putting the original negatives in the orthoprojector. This 
gives no difficulties in the orientation or profiling operations but 
it does, of course, mean that the negatives have to be cut from the roll. 
l4