132 GRAPHICAL OR NUMERICAL PHOTOGRAMMETRY?, AUTHOR'S PRESENTATION
,
Author's Presentation of the Paper
in the Meeting held on Friday, 9th September, 1960
Mr Harry has twice mentioned this after-
noon's subject, but not exactly in the way I have
understood it. The subject of my paper is
Graphical or Numerical Photogrammetry? This
paper has been published in Photogrammetria,
so it is not necessary to go into detail. I just want
to remind you of a few of the main facts which
are contained in the paper.
There are two groups of consideration in
making the choice between numerical and
graphical photogrammetry. The first lies entire-
ly in the field of the surveyor and is related to
the question of precision and that of organisa-
tion.
As far as precision is concerned, I do not
need to say very much. The efforts of the various
sub-committees of Commission IV have given
sufficient proof of the precision which can be
obtained. That the graphical method is slightly
in an unfavourable position with respect to the
numerical one is quite clear, because you in-
troduce there the errors in graphical presenta-
tion.
The second point is in relation to the cadas-
tral surveys. In most cases cadastral surveys also
belong to the terrain of the surveyors, so that the
decision about what type of photogrammetry
will be used can be said to belong entirely to the
field of the surveyor. Here some other consid-
erations come into the picture, especially con-
cerned with the organisation of the work; the
application of numerical photogrammetry opens
the door for systemisation and mechanisation of
the cadastral information. The instruments
necessary for this application exist and have
shown themselves to be available to fulfil the
task in this respect completely. They include
automatic registration of co-ordinates, attached
to the restitution instrument; high-speed com-
puters and auxiliary; equipment which is neces-
sary to use them. In many cases, however, a
graphical representation will be indispensable.
Its construction may be combined with the res-
titution instrument, but nowadays the existence
of co-ordinate plotters makes it possible to shift
the moment of plotting the result to another
stage of the procedure. Also, from a technical
point of view we may conclude that the appli-
cation of numerical photogrammetry will match
very nicely the demand for rationalisation of
cadastral administrations, but there remain a
number of problems to be solved. There is in
the first place the economic problem, the com-
plete set of tools for a cadaster in modern style
which requires considerable investment. Wheth-
er or not this is justified depends on local
circumstances.
A second point is the organisation of the
work which, if carried out consequently with
respect to an optimum efficiency, may be com-
pletely different from the existing organisation.
The easiest case is that you start a cadastral or-
ganisation right from scratch so that you do not
need to take into account existing organisation,
but there is still another point which should not
be forgotten: that the introduction of numerical
photogrammetry may have consequences of a
legal nature and in the first stage may therefore
lead to political arguments. I am thinking here,
for instance, about the question of the obligation
of marking boundary points. In several coun-
tries this exists; in others it does not. However,
if from a technical point of view it is concluded
that such a marking will be helpful and econom-
ically justified, then the question arises whether
such an application should be included in the
law or in some other legal rule. Furthermore,
who will pay for such a marking?
I hope I have indicated with a lot more
emphasis in my paper that a general answer to
the question of whether to use graphical or
numerical photogrammetry in a cadastral survey
does not exist. I consider it the task of Com-
mission IV to publish as much information as
possible about both procedures which should
be available to everyone who has to advise or
make decisions in this respect; the necessary
data which he can combine with his knowledge
of local circumstances will enable him to come
to a correct decision.
The application of topographical mapping
leads to a second group of considerations which
have an influence on the choice of numerical or
graphical. We can exclude aerial triangulation
because that belongs to Commission III.
Furthermore, from the title of my paper it is
clear that we are dealing with large-scale or very
large-scale mapping and not with small-scale
mapping, because there numerical methods
would hardly be necessary.
For large-scale topographical maps we have
in most cases not a purpose in itself but the maps
are meant to help, for instance, urban planning,
engineering projects or some other project,
which means that such a photogrammetric
process in general is part of a procedure which
started probably long before the need for maps
came up and will continue quite a time after
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