5 
3* Instrumentation 
The previous paragraph has inevitably dealt with some problems 
of instrumentation, but there are other aspects of this that are worth 
mentioning. 
It has always been recognised that one of the practical 
disadvantages of the analytical (digital) method of triangulation is 
that it requires, or was said to require, special apparatus for 
measurement, distinct from an analogue plotter. This is no disadvan 
tage to large organisations (Ordnance Survey of Great Britain, I.G.N., 
etc.) which have sufficient steady work of all kinds to justify 
installation df specialised equipment; but to smaller organisations, 
particularly perhaps private organisations, this could mean investment 
in equipment that is not continually in use. The last four years 
have seen a great revival of interest in the independent model or 
semi-analogue method which has the paramount advantage that it is a 
method employable with any plotting instrument that can record (not, of 
course, necessarily automatically) model coordinates. 
This last method has not only the advantage that any instrument 
can be used for it, but also that it should show accuracies greater 
than those attainable by the bild-anschluss method which relies to a 
greater degree upon the precision of the instrument. At least one 
organisation (The Directorate of Overseas Surveys of Great Britain) 
is now using the method exclusively and it is not being too rash to 
say that, as time goes on, and as deep-rooted prejudices are over 
come it will become the most popular method of aerial triangulation, 
at any rate with the smaller organisations. The increasing adoption 
of the independent model method is gratifying in another direction: it 
shows that photogrammetrists are becoming less frightened of arith 
metic. It was the desire to carry out all processes without calcula 
tion that so long delayed the adoption of methods involving a little 
calculation. It is certainly an additional reason why the fully 
digital method still continues to be unpopular; and perhaps the 
independent model method will, as I have said before, pave the way 
towards the adoption of digital methods which will have tp be used if 
the quality of the photographic data improves significantly. 
At the risk of being contentious or, worse, of saying some 
thing that everyone knows, it is perhaps necessary to reiterate the 
obvious fact that, because a plotter is more flexible and therefore 
more complicated, it is not, other things being equal, thereby more 
accurate. On the contrary, the simpler an instrument is, the more 
accurate it is likely to be for a given standard of manufacture, 
although it may have other disadvantages. Let us therefore cease 
to confuse universality with accuracy. The matter is very relevant 
to the problem of aerial triangulation as can be seen from the 
results quoted by Eden (I967) in Table III on page 487. 
But if the independent model method frees aerial triangulation 
from the more specialised and expensive universal instruments, it 
still suffers from the disadvantage that it is basically an analogue 
method which cannot for all practical purposes make allowance for 
asymmetrical lens distortions, lack of flatness of the film base and 
non-uniform film distortions. Recent work by P. Boniface (1967)