—4— 
make a correction for the incompleteness of the data and to give esti- 
mates of the yearly production. We have estimated that our cerd cata- 
logue is complete for 75%, but we are aware that this figure may be too 
high. If we accept this assumption we see that around 1965 the annual 
production reached a figure of 800 titles. One could say that, at that 
time, a researcher specialized in photo interpretation and willing to 
read all literature carefully was just about able to keep abreast, if 
he read two documents daily on an average, worked 6 days & week, did 
not take a vacation, had an assistant organizing a constant supply and 
did not do any research or practical work. Obviously, this is absurd, 
but it illustrates the fact. that to-day, even if all the literature 
would be readily available, it is entirely impossible for an individual 
to read all in detail. He has to nake a selection, and the more impor- 
tant is the existence of an efficient bibliographieal information sy- 
Stem with provisions for adequate Sorting. 
To conclude this section, let us have a look into the future. 
From the trend indicated in Fig.l we recognize an average annual in- 
crease in literature production of about 11,5% If we extrapolate this 
trend, we would expect about 1400 titles in 1970 and about 4000 in 
1980: 
Presently available bibliographical information 
For a survey of the present knowledge about photo interpretation 
literature as provided by bibliographies in the widest senge, it is 
adequate to distinguish between continuous bibliographies, i.e., bibli- 
ographieal information services with supplements appearing at regular 
or irregular intervals, and discontinuous bibliographies, i.e., data 
compiled as a one-time effort. For the latter, a list together with a 
subject and regional index has been compiled as a mimeographed appendix 
to this report and will be distributed to those interested on request. 
The bibliographies of the continuous type will be the main subject of 
this section. 
The first ard most important to be mentioned is the official 
"International Bibliography of Photogrammetry", which is produced by 
the International Institute for Aerial Survey and Earth Sciences (ITC), 
Delft, Netherlands, for the International Society for Photogrammetry 
since 1958. Important earlier literature has been included, however. 
For each document the bibliographical data and an abstract appear on 
à Library card of the international standard size of 7.5 on by 12.5 cm. 
e ® 
   
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