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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
2. ARCHITECTURAL ARCHIVE
An architectural archive concerns the detailed documentation of
monuments and buildings, which includes, in addition to the
descriptive information (e.g. history, style), the precise
geometry, the description of their present status, and the survey
of facades. With the present state-of-the-art, it can be said that
an architectural archive is a digital data base, geometric and
alpha-numeric, of a monument/building associated with its 3D
model. According to Carbonell (1989), although the
architectural archive belongs to the so-called architectural
precision survey, it is nonetheless a recording of a more
generalist frame, for, being less detailed, allows a systematic
documentation of the main monument/building. Figure 1 shows
one of the records (elevation) that makes part of an architectural
archive.
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Figure 1. Part of an architectural archive (elevation of a church)
An architectural archive is important from various points of
view: its drawings can be used as a tool when changes or
restoration of the monument/building are needed (Dallas,
1980); the recording of the monument/building is fundamental
when reconstruction is needed; it is also crucial for historical
studies (Carbonell, 1989); it may also be used to organize and
order existing data, facilitating the reconstruction of the past of
the monument/building, its interpretation and recording of
knowledge (Arnold, 2000).
An extra dimension added to the architectural archives is given
by modelling of the objects. 3D models allow to view the
objects from several view points, some difficult or even
impossible to attain in the real situation due to the object itself
and/or its surroundings (El-Hakim e/ a/., 2002). Furthermore,
they allow a virtual interaction with the object (visualisation of
changes for helping in decisions); creation of virtual museum
and tourism, allowing, for example, the virtual entrance in
buildings that are closed for security reasons.
To create an architectural archive there are several
requirements, including the scale and precision which may vary
from 1:50 to 1:100 and from 2 to 5 cm, respectively (e.g.
Carbonell, 1989; Scherer, 2001). Techniques that may
guarantee these requirements are Photogrammetry, and more
recently Terrestrial Laser Scanning.
3. 3D URBAN MODELS
JD urban models are a three-dimensional representation of the
urban environment, which is a simplification of the more
general environment. It represents buildings as well as other
man-made structures. To improve the visual appearance and to
make it more realistic, certain details need to be added to the
geometric models and, if possible, other types of functions
(such as virtual walks) and information. In this way, the
gcometric part of the models has to be handled with visual and
animation techniques.
3D urban models are used for several applications such as urban
planning and management, architecture, virtual reality,
simulation studies (e.g. telecommunications, catastrophes),
tourism, and environmental impacts.
The procedure to create 3D models can be divided according to
Figure 2: planning and acquisition of data, data processing, and
modelling and rendering. By modelling we understand the
geometric reconstruction of the object, whereas by rendering
we mean modelling of textures and light effects to make the
models more realistic during visualisation.
Planning and
Data
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Acquisition
Y
Data Processing
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Modelling and
—| Rendering
Figure 2. Main processes to create 3D urban models
Obviously, the creation of a 3D model is dependent of its
intended use - for virtual tourism the geometric precision is less
important then the visualisation effects, whereas for some
studies both geometric precision and photorealistic effects are
important. This intended use of the model has to be taken into
consideration in the planning phase.
4. VISUALISATION
The visualisation of a 3D model, be it of an object or urban,
aims at valorizing the model through its presentation and by
making its divulgation attractive and available to a great
number of users.
Visualisation may be done with simple images, or, as it is done
in this study, using more sophisticated means that allow a
greater closeness to reality. Animations and the creation, for
example, of a multi-media recording on a CD-ROM are another
efficacious means of divulging the 3D models and associated
information (e.g. location and historical description of the
surroundings), contributing to the public awareness of the
cultural patrimony.
Visualisation is thus the ultimate stage by which the 3D models
are made known and available for several applications. This
implies that the 3D model's format should comply with
international standards, allowing for interactivity, as for
example the language VRML (Virtual Reality Modelling
Language) for distribution on the Internet.
