130 GRAPHICAL OR NUMERICAL PHOTOGRAMMETRY?, V D WEELE 
3. Simultaneously, or subsequently, the terrestrial determination of supplementary con- 
trol (if necessary) including levelling or trigonometrical heighting may be executed. 
4. Execution of the flight. 
5. Restitution of the photographs, aerial triangulation, plotting and computation. 
The critical point, as far as time is concerned, is the execution of the flight. With 
regard to the vegetation the photographs should preferably be taken in the end of winter 
or in the early spring, on areas of deciduous forest, and provided of course, that there 
are such seasons. If everything succeeds the first results can be delivered during the 
summer. This means in fact that the decision, mentioned under 1 should be taken well in 
advance and that at least half a year but probably more time should be reserved for the 
total procedure. To have the full advantage of the photogrammetric method a good liaison 
and understanding between the technical director of the project and the photogrammetric 
organisation is a prerequisite. This understanding is necessary in the first place to get 
a well-balanced decision on the question of whether photogrammetry is an appropriate 
method for the special case and secondly to have the organisation of the photogrammetric 
work fitted well into the planning process, and thirdly to interpret the results and to 
take into account the special properties of photogrammetry. The conclusion is certainly 
reached that good results can only be expected if the civil-engineer and the photogram- 
metric expert form a cooperating team. This team should also include the man who is 
responsable for the computations and who has to make his programmes according to the 
wishes of the civil-engineer, but based on the data that photogrammetry can make 
available. 
To what extend the computer will be able to answer the questions that the civil 
engineer may put is not yet clear. It may be expected that the number of programmes to 
answer many of these questions will increase in future. They may include for instance 
the calculation and comparison of variants of the project, the computation of setting out 
data, etc. etc. The problem of giving the answers at the appropriate moment is a matter 
of organisation and foresight and this should be solved by a combined of the three mem- 
bers of the team. The question of the economy of the numerical solution of many problems 
can only be answered on an experimental bases. Up to now data for a good judgement 
seem not to be available. A greater difficulty will probably be met if factors, which are 
difficult to express in a tangible, or digital form have to be included. The location of a 
road in sparsely populated terrain may perhaps be treated as a problem of a mainly 
mathematical character, where conditions can be included with respect to minimum or 
maximum value of horizontal and vertical radii, a minimum of transport of material 
etc. etc. It will, however, be more difficult if different qualities of foundation have to 
be taken into account. Such complications reach probably their maximum in densily 
populated areas where different types of culture, desirability of avoiding protected 
natural parks, political considerations and those types of governing factors have to be 
taken into account in reaching a decision. It is still an open question if, in those cases, 
the integrated numerical system is able to treat the problem in an economical way. 
It may be expected that in future the better (or best) solution may be found if 
photogrammetry is still more adapted to the special requirements of the civil engineer, 
but also if the latter adapts his procedure and requirements to the possibilities of 
photogrammetry. Both have to be aware of the qualitative and quantitative capacity of 
the third man in the team who represents the mathematical and computational part. 
The question of who will be the chief in this team, depends on the circumstances, 
but should not play a decisive role in real team-work. 
Generally the civil-engineer will represent the greatest, financial interest in the 
project, and hence, he will probably have the decisive vote in the team. Other solutions 
are, however, also known.