68 
include the provision of an improved means 
of determination of instrument height. In 
providing control for the photogrammetric 
survey of a high structure, probably the most 
critical observation lies in measuring the 
height of the theodolite trunnion axis above a 
levelled ground mark (Atkinson and Proctor, 
1970). The same criticism is valid if camera 
co-ordinates and exterior orientation data are 
being determined, as Erlandson and Veress 
(1974) have pointed out. They also call for a 
manufacturer's calibration, to the same accu- 
racy as the principal distance, of horizontal 
and vertical eccentricity constants. 
However, these are relatively minor points 
when considered in the overall context ofthe 
advancement of close-range photogram- 
metry. We should not seek to oversell these 
techniques, for that could be extremely un- 
fortunate and counter productive, but we 
should endeavour to promote the use of 
photogrammetry in appropriate cir- 
cumstances. Proctor (1973) considered that 
"just so long as the practice of photogram- 
metry remains mostly the prerogative of the 
surveyor there will continue to be a sales 
resistance mitigating against its acceptance 
in other disciplines." Commission V of the 
International Society for Photogrammetry 
should strive for that necessary diversifica- 
tion. 
ACKNOWLEDGMENTS 
I am indebted to O.W. Cheffins, A.H.A. 
El-Beik, R. Farrand, M.W. Grist, J.E. Hard- 
ing, W. Heath, the late R.I. Horder, J.F.A. 
Moore, I. Newton, G. Owens, A.N. Schofield, 
P.J. Scott and G.A. Stoker for correspondence 
and discussions about their work over a 
period of several years. Projects which have 
been carried out at University College Lon- 
don could not have been undertaken without 
the active support of Professor E.H. 
Thompson and my colleagues in the Depart- 
ment of Photogrammetry and Surveying. 
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