F. Polzleitner, “The Wild PPO-8 orthophoto equipment” 
K. Szangolies, "Technique and accuracy of the differential rectification with 
Topocart-Orthophoto-Orograph 
C. Vigneron, *Orthosform Type 9300” 
M. Thonus, “The 3rd digital control camera’ 
W.S. Ferri, The Galileo-Santoni Orthophotosimplex and some accuracy tests". 
The first question, posed to the panel, was: which of the three possibilities for transferring images in 
orthophoto production, namely direct, optical or electronic, is the most desirable? As far as image quality is 
concerened, a number of panel members expressed their surprise at the amazing quality of the electronic 
images, and quantitative tests have shown that this approaches the resolution of optical systems, although it 
was argued that it is difficult to predict the exposure in electronic systems. On the comparison of these two 
systems, it was remarked that electronic systems cannot yet provide colour orthophotos. As far as correlators 
are concerned, although these are as yet unsuited to large scale work, there was general agreement that 
automated systems would be faster, and would reduce operator fatigue. Attention was also drawn to the 
possibility of producing orthophotos automatically from contours, a significant advantage for revision 
purposes being the fact that the shape of the terrain hardly changes. 
Opinions seem to differ on the question as to whether orthophotos should be produced off-line or on-line. It 
was argued that the off-line systems are twice as expensive as those on-line, and, in principle, there should be 
no difference in the production times since the choice of slit width is determined by the required accuracy; but, 
on the other hand, production rates in West Germany indicate that the off-line system is 2 1/2 times faster, 
indicating that the extra equipment costs can be amortised within a number of years. Other advantages of the 
off-line system include the facts that: provided pin-point photography is supplied, the stored profiles can be 
re-used for map revision; and, also, that a single printer can accommodate 3 to 4 plotters, the printer requires 
lower skilled personnel, and lends itself to 3 shift operations since it is less tiring for the operator. 
As regards the optimal ratio between photo and orthophoto scales, the advantages of equipment having the 
possibility of a variable magnification, and of being able to produce double models, were emphasised. 
However, the enlargement ratio was also considered to be dependent on scale, since if a sheet is to comprise 
3 or 4 orthophotos, the difficulties in handling the photographic material will limit the enlargement to some 
4 times. 
The discussion then turned to the problem of applications of orthophotography, the following presented papers 
being first read by title: 
P.S. Alexandrov, ‘““Ortho-transformer of the TZNIIGAiIK” 
H. Kasper & T. Schenk, “Development of height profiles from model co-ordinates’ 
H.B. Loving, “Status of the USGS automatic orthophoto system’ 
J. Gebry, ‘““Radial allotted orthophotoscope’ 
W.S. Ferri & M. Fondelli, “Applications and developments in orthophotography”’ 
J. Jornstad & P. Kaasila, *Orthophotomapping in Sweden". 
The first question put to the panel concerned which of the following products - photos, controlled mosaics, 
orthophotos, stereo-orthophotos, or line maps - are to be recommended for various purposes. The planimetric 
errors present in aerial photographs are well known, as is the fact that orthophotos are more suitable than 
mosaics in the hillier types of terrain. The advantages of orthophotos over line maps are fairly evident in desert, 
jungle and swamp areas, where the end product is enhanced by the detail present in the photographic image, 
but it was doubted whether these would replace line maps in urban areas. Little can be said on the comparative 
costs of the two systems, but the time element must also be considered. The limitations of a number of these 
map-substitute products must therefore be placed in their proper perspective, considering that a lack of even 
intermediate maps can hamper the development of a country. 
The problem of height information was discussed next, there being general agreement on the fact that the 
accuracy of contours, derived from profiles, is about half way between the accuracies of contours plotted 
directly in a stereo-plotter, and those derived from drop lines. Interest was also shown in the Russian method 
of automatically producing orthophotos from contours. 
There being no time left to discuss the last two questions on applications and reproduction problems, the 
Chairman closed the session, thanking the audience and the panel for their lively contributions.