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60 LA COMPENSATION DES BLOCS DE BANDES, PRESENTATION
La deuxième partie donne un aperçu systématique des diverses méthodes actuelle-
ment utilisables. Ces méthodes ont été classées de la façon suivante:
1. Triangulation radiale.
2. Stéréo-templet.
3. Aérotriangulation spatiale: Méthodes reposant sur la compensation individuelle
préalable des bandes qui composent le bloc, méthodes de compensation simulta-
née d’un ensemble de bandes, méthodes de fragmentation du bloc, méthodes re-
posant sur l’utilisation de calcul automatique.
Pour chaque groupe, le rapport s’efforce de faire ressortir les avantages et les in-
convénients.
En conclusion, on peut dire qui’il existe actuellement plusieurs solutions approchées
qui ont été consacrées par la pratique et ont prouvé leur efficacité; le choix entre ces
solutions dépend des conditions particulières du problème cartographique à résoudre.
Mais le développement très rapide des puissants moyens de caleul modernes a permis
récemment la mise au point de solutions théoriquement plus rigoureuses, mais qui exi-
gent la possibilité d’utiliser un calculateur automatique à grande capacité.
Presentation of the Paper by Dr H. G. Jerie
I was chosen to assist Mr Bonneval and I
will try first to give some introductory remarks
which are based mainly on the essential feature
of Mr Bonneval's report.
Mr Bonneval pointed out that the general
requirement for the block adjustment method
will be the following: first, of course, all co-
ordinates have to be in one uniform co-ordinate
system; secondly, they have to be homogeneous,
and if possible high relative precision will be
required; thirdly, absolute precision is required
that will be satisfactory to the topographical
task; lastly, of course, the lowest possible cost
should be connected with such a block adjust-
ment method, but this cost has to include all
procedures — namely, aerial photography,
ground control, aerial triangulation work itself,
computation and adjustment. So we cannot
allow that only the adjustment method itself is
evaluated in respect to cost, but also the com-
plete procedure.
In the evaluating method we have to consider
the following circumstances in our work: first,
the kind of area, whether the area is easily
accessible, and the density of existing ground
control; then the time available for the project;
the existing material; machines and personnel,
and, of course, also the skill of the personnel.
We then have to consider the precision requir-
ed, and we have to ask whether a method
allows us to use existing ground control, or
whether a method forces us to get the ground
control on very special places, which would
mean that a special ground survey has to be
done. Last, the security of a method with respect
to blunders and gross errors has to be con-
sidered.
In the next chapter, Mr Bonneval gives a
survey of the existing or proposed methods in
block adjustment. The first subject of a block
adjustment could be radial triangulation, es-
pecially numerically radial triangulation, but
this could be treated just like the normal slotted-
templet adjustment of radial triangulation strips.
We have to regard this as a block adjustment
method. It is the oldest, the fastest and the most
efficient method in block adjustment, and pos-
sibly the most used tool, but it gives only
graphical precision and it cannot be used for
large-scale mapping. However, I do not think
that it is really a problem for this meeting here.
Then we have to deal with spatial and analytical
air triangulation. I have here considered them
together as we can say that analytical air trian-
gulation will be either adjusted according to
rigid methods, as proposed, for instance, by Mr
Schmid or Mr De Masson d'Autume and some
others, or it can be adjusted according to ap-
proximative methods which are then basically
equal, and then adjustment of aerial triangula-
tion strips.
With regard to spatial aerial triangulation, we
can distinguish between numerical solutions,
such as adjustment of independent strips and
taking the average of the co-ordinate obtained
in this strip adjustment, the method of cross
strips as proposed by the school of Professor
Zeller. Then there are second or third order
functions for the correction of the co-ordinates
which are found simultaneously for the whole
stri
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