GRAPHICAL OR NUMERICAL PHOTOGRAMMETRY?, V D WEELE 129 
The fact that photogrammetry can produce planimetric maps completed with contour- 
lines or spot heights of sufficient precision to be of great help in planning of technical 
features will be taken for granted. 
For the computations of quantities of earth or rock, to be displaced, profiles of the 
terrain are frequently used. These profiles can be constructed from data, taken off from 
the map but a quicker procedure is that the profiles are plotted directly from elevations, 
read in the instrument, of points which on the plotting table, lie on a straight line. 
The next step, however, is that the profiles are obtained only in digital form, using 
an instrument provided with automatic registration, and that this registration in the 
form of punched-cards or punched-tape is used for further computation, 
Publications show that, with this procedure, a complete computation of quantities of 
cut and fill is possible and even that, with an appropriate programming, the optimum 
location of the axis of a road could be determined by computation. 
Descriptions of the instrumentation for these and similar applications of numerical 
photogrammetry can be found in literature or will be presented to this congress. It may 
be expected that the development of techniques will, in future, improve the procedure 
and widen the scope of applications from the technical point of view. We will, therefore, 
not enter into this subject for the moment, but pay more attention to some other problems 
involved. 
IV.b. 
From an economical point of view it is not sufficient to compare the cost of the 
modern numerical and the older graphical method as such. It is quite probable that, if 
the amortisation of the special devices and of the computer, are taken into account, the 
numerical method will cost more. The saving in time, which is possible by this method, 
however, may give a much greater saving in the cost of the total project so that the in- 
vestment may be completely justified. The saving in manpower, especially in countries 
where sufficiently skilled personel is scarce, may be another justification for the higher 
cost. 
Generally a photogrammetric contour map - a graphical product — is also desired 
since it gives a better representation of the terrain and, as such, is very valuable in the 
detailed planning phase. 
The advantage of digital profiles, versus graphical ones, is their suitability for 
automatic computation. 
A combination of graphical and numerical methods seems therefore to be the most 
suitable. 
IV.c. 
The main problem seems to lie in the organisation of the work. A general scheme of 
the procedure may illustrate this but it should first be noted that we will start at the 
phase in the development of the project where data, obtained from rather large-scale 
photographs, are required for detailed planning and for execution. The diversity of means, 
used for the preliminary phases of the project is so great (e.g. small-scale photographs, 
existing topographical maps, reduction of cadastral maps ete.) that no general procedure 
exists. 
Additionally, in these phases, the question of graphical versus numerical photogram- 
metry does not arise. 
The photogrammetric procedure exists in: 
1. Decision about the application of photogr. followed by an examination of existing 
control and the set-up of a flight-plan. 
2. Signalisation of terrestrial points and of new control for setting out the project, for 
completion-measurements etc. 
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