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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
In the period of analogue photogrammetry production of
technical documentation was based exclusively on using glass
plates or films. Graphical stereorestitution of such images was
conducted on analogue photogrammetric plotters (special or
universal ones).
Advances in technology of making technical documentation
after introducing analytical photogrammetry were reflected in
the following (comparing to analogue):
e more flexibility of analytical instruments in the
orientation and stereorestitution of terrestrial images;
e possibilities of using non-metric and semi-metric
cameras;
eo more flexibility in photography planning (locations
and orientation of camera)
Nevertheless, the most important issue in making technical
documentation — archiving and production of graphic
documents, remained in analogue form. Critical changes in
photogrammetric application have happened with the
introduction and expansion of digital phtogrammetry.
4. DIGITAL PRODUCTION OF TECHNICAL
DOCUMENTATION
Appearance of digital photogrammetry has opened completely
new possibilities in production of technical documentation for
cultural heritage. Changes were very important and they pertain
not just on already existing phases, like:
e image capturing,
e graphical documentation production,
e archiving, :
but also on possibilities to produce completely new digital
products:
e digital orthophoto and
e 3D object model.
4.1 Image capturing
First of all, the new possibilities occurred for photography in
digital technique. Of course, already existing terrestrial
photography techniques are still useful, providing that high
quality scanning is included. Non-metric (amateur) and semi-
metric cameras can be used also because after scanning
procedure all systematic errors could be corrected by applying
digital resampling. Imaging became far flexible and faster
cause, beside normal stereo pairs, images can be taken by the
hand, from completely arbitrary position.
4.2 Archiving
Archiving of source material is based on using digital media
only. In that way, the loss of photo documentation quality
during the time is excluded. Of course, even digital photo
documentation cannot be absolutely protected, but with proper
archiving methods this problem can be brought down to
theoretical level.
43 Orhophoto production
Digital form has opened new possibilities for digital orthophoto
production as very fast and inexpensive part of technical
documentation (Baratin et al. 2000). This procedure is based on
similar process as in aerial photogrammetry. Important savings
can be done by simplifying digital elevation model (DEM)
requirements. This means that for some simple facades DEM
can be replaced with vertical planes.
4.4 3D object model
Completely 3D object model can be produced, providing that
reasonable financial resources are available, or when user
requests are higher (Kólbl et al. 2000; Dorffner et al. 2000). The
process of 3D object model creation can be done by digital
stereorestitution, automatic measurement of 3D model based on
image correlation or by combination of both. Nevertheless, it
should be noted. that every object has its own specifics, so it is
very difficult to formulate the standard procedure. That is why
this product is not compulsory part of technical documentation.
If the final goal of technical documentation is 3D object model,
then it should be estimated whether digital photogrammetry is
more economical then 3D laser scanning (Boccardo, Comoglio
2000).
5. PROCEDURE FOR MASS PRODUCTION OF
DIGITAL TECHNICAL DOCUMENTATION
Procedure that is to be proposed in this paper is the result of our
own experiences in application of photogrammetry for cultural
heritage in Serbia by using already mentioned advantages of
digital photogrammetry. Intention is to establish initial technical
documentation for a number of cultural monuments and objects
with high architectural value.
5.1 Assumptions
The basic assumption for formulating procedure is that it has to
serve in campaign-type and systematic way of working, with
intention to enable a lot of savings. Therefore, important role in
procedure formulation was financial aspect of photogrammetric
application. That is why the procedure is based on the following
hardware and software assumptions:
e For image capturing Rolleiflex 6006 is used (colour
film); :
e EPSON Expression 1600 desktop scanner is used for
scanning;
e Total station Leica TCR705 is used for determination
of control points (reflectorless);
e Geometric rectification of scanned images is
performed by DigiScan 2000 (www.mapsoft.co.yu)
e Any available software can be used for digital
triangulation;
e Some low cost software can be used for
orthorectification.
5.2 Basic idea
Procedure of technical documentation production is divided
into two logical phases. The first consist of image capturing,
necessary field measurements and production of archive
documentation. Archive documentation is completely digital
and consists of three units:
e digitised and geometrically rectified photogrammetric
images,
e digital orthophoto as preliminary documentation, and
e technical report in digital form with all the
information on object and technical data necessary for
further photogrammetric works in the second phase.