CIP A 2003 XIX! 1 ' International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
often indicated as being the central element for the constitution
of an architectural solution (Prost, 1992). Thus the availability
of a model of the existing buildings seems significant to us.
For Lebahar in 1983, the drawing was the means of acting on
the object, and on "himself (the architect) acting on the object ".
Nowadays, CAD is an alternative to the drawing and allows
similar situations. In order to initiate a building project, one
should be able to view it in the final context in which it will be
inserted. A building in the design phase does not exist, but its
future environment generally does. A representation of the
existing context is thus significant. Models at various scales
have been used for a long time to visualize three-dimensional
architectural objects. Now data processing is developing in the
agencies, and we should consider the benefits this 3D
visualisation tool brings.
3.1. Virtual model available today
Only what is necessary for the desired final model is modelled
during a restitution (using the photogrammetry software), once
images have been oriented (fig.2). However, in the case of an
architectural intervention, part of the potentialities of a building
are discovered at the same time as it is measured. Thus the
interest of the model evolves according to its own advance.
3.2. Volumetric 3d model
Data processing proved itself in the area of the architectural
drawing. It is concievable that the use of it will extend to the
design, even if hand drawing keeps an undeniable role. During
this significant stage of the project, several implementation and
volumetry alternatives will be tested, and they will be confirmed
(or not) by their traditional model representation. 3D modellers
are increasingly being used. Consequently a 3d model of the
existing becomes essential. However urban 3d models are not
yet available for the designers as are 2d computerized plans
(Morakot, 1996.). Multi-image Photogrammetry allows a quick
and easy making of 3d models (for a smaller intervention scale).
In order to carry out this 3D model, the data will be obtained
from virtual models and it will be used immediately to model
the volumes of the buildings (fig.2). Trying to bring back whole
volumes with the photogrammetry software would be too
tiresome. A topographic plan can be used as a starting point if it
exists (Chevrier & Perrin, 2001), by extruding the lines
describing the buildings, and by slicing the volumes, one after
the other, depending on the data provided by the
photogrammetric model. A 3D model is not an accurate model,
it should be used to give the scale of buildings, not to provide
details on openings and ornaments.
Figure 2. Three possible uses of the 3d data issued from
photogrammetry
3.3. Textured 3D model
The textured model (fig.2) directly results from the data-
processing tool for architecture representation, as opposed to the
3D model, which comes from traditional model. It allows a
virtual insertion of the project in its closer architectural
environment. It is possible to choose the point of view, to
represent the project in perspective, after inserting it in the 3D
model.
The easiness of the proposed tool is one of the critical success
factors for the architect to use photogrammetry. This is why a
"turn-key" tool must be made available.
4. HOW TO INTEGRATE PHOTOGRAMMETRY IN
THE ARCHITECTURAL DESIGN PROCESS
4.1. The architect as photogrammetry user
The architect must use this tool himself. It is one of the success
factors for a tighter cooperation between photogrammetry and
architecture. Several tools are used alternatively throughout
architectural design process. If photogrammetry is directly used
by the architect, it becomes a tool which he can constantly use.
The photogrammetrist should by no means be excluded from
the architectural project process, but photogrammetry principles
should be integrated among the architect tools. This is why we
do not think a human interface is suitable. Even if know-how is
larger, the presence of an intermediate specialist can slow down
the process. The project would be jammed if the architect had to
permanently translate his needs in order to use one of his tools.
Moreover he may not be able to exactly define his wishes as
seen in chapter 2.1. To make this tool available to the
architectural project, it should be democratized, even at the
expense of some accuracy or rigour in the survey. The goal here
is not to convince of the absolute need for the use of
photogrammetry in the frame of the project but to show which
services this technique can return to those who control the
principles of it.
4.2. Data processing as a link between the two disciplines
Resorting to data processing is one of first requirements to use
the photography survey tool, because the information produced
by photogrammetric techniques is of digital nature. Contrary to
the computer-assisted presentation, CAD is not very much used
yet in architecture but a lot of research is under way, specially
dependent on progressing technologies. The introduction of
photogrammetry into the architectural design process may also
generate demand for CAD for architects who would not have
yet found a good reason to adopt it as a working tool.
5. TYPES OF ARCHITECTURAL INTERVENTIONS
FOR WHICH PHOTOGRAMMETRY IS EASILY
SUITED
In order to use photogrammetry in the architectural project, the
built context has to be appropriate. That is why we distinguish
between two kinds of projects.
Rehabilitation projects and insertion projects between buildings:
their contexts influence the course of the design. The documents
used to represent this context are already an interpretation of the
place. An elevation only shows a part of information. A picture
only shows part of the whole object. Thanks to photogrammetry
the entire context is available in digital and global form.
Photogrammetry makes a virtual object available to the user,
which can constantly provide information about dimensions as
well as about materials of the considered object.
