ANALYTICAL AERIAL TRIANGULATION 
1. MONOCULAR AND BINOCULAR OBSERVATIONS 
Since the London Congress of 1960 perhaps the only basically new development 
in analytical aerial triangulation has been in revival of interest in monocular obser 
vations and it should not be out of place to raise a few points in connection with 
this. Any technological process has two important aspects: economy, in the broad 
est sense, and accuracy. When one is discussing whether a particular process is 
«better» than another it is of some importance to decide with which of these two 
aspects one is concerned. One may be concerned with both, but it is then surely 
important to make clear at any time which is being talked about. Do we now 
have a feeling in monocular and binocular discussions that the distinctions between 
the two aspects is not sufficiently clearly drawn? 
There is very little doubt that the time that has to be given to preparatory work 
in aerial triangulation can be grossly underestimated in the minds of those who 
are concerned with developing methods and designing instruments; and it is there 
fore salutory that this aspect should be brought out into the open and not treated 
as something of little importance to be swept under the carpet. The results of 
systematic studies of block adjustments by the method of least squares, first with 
the Jerie analogue apparatus and later with automatic digital computers, have 
shown how important it is to regard the block as an isotropic lamina and that, at 
any rate in plan, the transfer of position, scale and orientation from strip to strip 
is at least as important as its transfer from model to model within the strip. With 
heights it is otherwise and we will return to this problem later. The conclusion 
that must be drawn is that the identification of points common to strips is at least 
as important as the identification of points common to models within a strip. This 
means, in its turn, that some way of providing for such identification becomes 
imperative; and a sound and practical method is to pre-mark the points with a 
stereoscopic marker such as that made by Wild. The natural (but not necessarily 
logical) step from there is to pre-mark all points in this way and dispense with 
stereoscopic measurement altogether. It would look, at first sight, to be an attrac 
tive proposition from the first of the two aspects that were mentioned above: 
economy. The apparatus should be cheaper, for the point-marking device, while 
stereoscopic, is not a measuring device and the monocular coordinate measurer is 
half a stereo-comparator. Again, preparation and measurement are neatly divided 
and, on the face of it, could be better organised. In principle the monocular 
measurements to well-defined artificial marks could be automated relatively easily 
as, indeed, they are already for the measurement of star plates.