affectedby image movement for those orthophotos which were produced with a 
slit wider than 1.5 mm (in the orthophoto scale 1:2 500). No image blur 
was detected for the orthophotos produced by electronic image transfer on 
the Gestalt Photo Mappers I and II since, on these instruments, the ortho- 
photo image of each elementary area is printed ina stationary mode. Also 
the orthophotos produced on the Wild OR 1 and PP0-8 with slit widths of 
0.1 mm and 0.2 mm, respectively, were free of image blur. 
Closing Remarks 
Even when the primary purpose of this study has been to determine 
the general performance of the orthophoto technique, a comparison between 
various instruments available on the market could not be avoided. This 
restricts the authors' freedom to express their own opinions as to advantages 
or disadvantages of different instrumental solutions. Therefore, the authors 
refrained in this report fromany exposition of their own points of view and 
only presented the results obtained, limiting the discussion to some factual 
explanations. In addition, they made every possible effort to assure that 
the individual results are correct and meet in general terms the approval of 
the participants. To achieve this, the individual initial results were 
reported back to the participants with a request for corrections, comments, 
or suggestions. Moreover, before the final report was prepared for print, 
one of the authors, M.C. van Wijk, personally contactedmost of the partici- 
pants discussing once more the results obtained on their instruments. 
However, at no time were the results of one participant communicated to the 
others, or to interested third parties (users). 
One of the main conclusions that should be drawn from the experiment 
is the excellent geometric quality of orthophotos and the related height 
information. If there is a limitation to the use of the orthophoto techni- 
que, the reason for it is definitely not its accuracy, which is more than 
sufficient in most mapping operations in which a graphical product is the 
goal. The fact that the orthophoto technique is fast, inexpensive and also 
provides pictorial information, of importance to many disciplines and fields 
outside conventional mapping, is an added advantage and attraction which 
should be seriously considered, particularly by developing countries in need 
of all kinds of basic land information. 
The image definition achieved by some of the instruments is 
impressive and only a relatively insignificant loss of quality could be 
detected as compared with the original photographs. In viewof new repro- 
duction techniques which are presently being developed andwhich, hope- 
fully, will permit screen-free reproduction of orthophotos and orthophoto 
maps, a high image quality of orthophoto products will acquire even more 
importance than it already has. 
The authors regret, that inorder to meet the original deadlines, 
certain orthophoto products which were submitted too late could not be