and resolution of digital images. Application of very
precise scanners is sometimes difficult and costly. Thus
research into the accuracy of popular scanners
improvement by introducing suitable geometrical corre-
ctions is developing wider and wider. The readability of
details is decided by the resolution of digital images.
Resolution of the order of 2400 dpi or even 1200 dpi can
be practically satisfactory. However plotting is often
performed on images with a resolution of 600 dpi
because of the still existing difficulties in storing and
making accessible large files of digital images (a 230 x
230 mm photograph scanned with a resolution of 600 dpi
forms a file of 30 MB or of 120 MB in the case of a
resolution of 1200 dpi). However it can be expected that
the fast development of exchangeable magnetic and
optical-magnetic hard discs will soon lead to an easy
operation of even large files containing digital images.
All the existing historic monuments, such as: urbanistic
complexes and single buildings, architectural details,
furnishes, wall paintings and sculptures, as well as
archeological excavations - all of them should be
documented, also with proper surveying records. The
surveying documentation scale depends on the object
size and use, and can range from topographic scales to
very large ones. The documentation must comprise
drawings or numerical models which enable production
of variety of projections, including developments,
crossections, axonometric views and others.
Various techniques are used to survey historic
monuments. For many cases photogrammetry could be
very useful, but till present times it was recognized as
very efficient but rather expensive method.
Very fast development of digital photogrammetry makes
it potentially possible to apply analytical methods even
without approaching a specialized photogrammetric
laboratories. Well, but off shelf, equipped computer room
makes the photogrammetric restitution possible. The use
of highly specialized software and ordinary analogue
and/or digital cameras make restitution feasible.
In such situation - when most difficult technological
problems can be solved by computer software -
photogrammetry becomes not only less expensive, but
also much easier. It does not require high specialization
and long training any more, and can be practiced even by
non-photogrammetrist. It would be true, under condition,
however, that the technology as well as equipment are
properly adapted to be operated by non-professionalists.
The system named Video Stereo Digitizer was developed
during recent years at the Dept. of Photogrammetry and
Remote Sensing Informatics of our University. It can be
implemented on the DOS operating personal computers
of 386, 486 and better series, equipped with SVGA
graphic monitor and mirror stereoscope to observe split
screen stereopare presentation. VSD is fast and efficient
enough for the purpose it was designed for. Experimental
works have shown good restitution accuracy of aerial 23
X 23 cm stereopares, and even when utilizing aerial
pictures taken with 6 x 6 cm photographic camera. Also
plans of facades of historic church or vectorial
documentation of sculptures were plotted with good
result.
That type of a stereo restitution system, when equipped
with properly designed specialized functions can suit
also the non-topographic applications, namely the
historic monuments documentation requirements. Being
260
inexpensive, applicable on off-shelf hardware, easy and
efficient in use such small specialized digital
stereoplotter can find room in many laboratories as a
typical tool for historic monuments and sites
photogrammetric recording by non-photogrammetrists,
eg: conservationists and archeologists.
2. GENERAL OUTLINE OF FUNCTIONS OF A SMALL
DIGITAL STEREOPLOTTER DESIGNED FOR
HISTORICAL MONUMENTS AND SITES RECORDING
AND SOME HINTS FOR THE SYSTEM
CONSTRUCTION
The recording of a historic sites is usually requested by a
restoration team as a material for their studies and
restoration design. Entire ,as found” record comprises
maps (1 : 500 to 1 : 200), vertical and horizontal cross-
sections, facades, developments of vaults and walls,
projections of domes (all that in the scale of 1 : 50 or
even 1 : 20), and records of details (1 : 10 to 1 : 1).
Archeological excavations need systematic periodical
recording, to assure a proper documentation of
successive layers which disappear one after another.
This makes photogrammetry indispensable in recording
of historic monuments of architecture and art, and in
recording of archeological sites.
The modern methods allow for evaluation of pictures
taken with any metric or nonmetric camera what makes
much easier and broadens the range of applications. The
demands for photogrammetric recording of historic
monuments and sites is great and does not decrease
[Waldhausl, 1992].
Necessary field works require from the recording team
some knowledge of photogrammetry, as the hand-
survey, stereopairs, and various large scale shots which
supplement the survey should meet not only the historic
structure requirements but also the feasibilities of plotting
techniques. Thus, beginning a new project, one foresees
various kinds of drawings, their scales, and contents.
Also the appropriate pattern of final presentation should
be chosen at that early stage of each project..
One or more of the following patterns of presentation can
be used for the final presentation of historic structure
[Jachimski 1976]:
- linear drawing (vectorial presentation)
- linear drawing supplemented by photomosaic
- photomosaic supplemented by linear drawing
- photomosaic
Nowadays, the linear drawing is still a predominating
pattern for the presentation of architectural record.
Photomosaics are used rather rarely (due to the fact that
the majority of architects is yet not used to it), but with a
good result [Hokey, 1973, Wanot 1968] Interesting
experimental works on orthophotography proved the
purposefulness of this technology for a certain type of
historic objects.
The compiled patterns however, are most likely to
become a future standard for monument presentation
when utilizing the photogrammetric survey. This very
useful combination of the linear drawing and
photomosaic (rectified photography or orthophotography
in various projections) can satisfy the accuracy demands
and the minuteness of detail. The often expressed need
for selective exposure of the most essential details of a
structure is also assured. The editor of a record has a
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
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