T 48- 
Vermeer, Jo, 1968 — Results of an objective comparison of 
film-filter combinations applied to an 
example of photo-interpretation for soil 
survey. ITC-Delft; Transactions 11th 
congress ISP, Lausanne pp 22, 
Vernon, M.De., 1962 - The Psychology of Perception. pp 265 
Pelican A 530 (Penguin Books Ltd, 
Harmondsworth, Middlesex). 
Zorn, H.C., 1965 = An Instrument for testing stereoscopic 
acui ty. 
Photogramnetria 20, p. 229-238. 
Acknowledgements 
It is a pleasure to mention here the assistance of, and the discussion with, 
K.K. Rampal of the Indian Institute of Technology in Kanpur, who also carried 
out most of the recent experiments, mentioned under par, T. If only he could 
have stayed longer than one month, & co-authorship would have been natural, e & 
With staff and students of the various interpretation-branches, in the 
Natural Resources, the Integrated Surveys and Social Science departments, the 
author had the possibility to discuss and learn about their opinions. As a 
staffmember of the Photogrammetric Department, the contacts within the team 
were inspiring and helpful particularly for facts about stereo acuity. 
Last, but not least, the administrative and technical staff made it possible 
to finish this paper in time — some know about the struggle against "fatigue" 
and the "time arrow".