CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
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Tacheometry necessitates special skills and therefore
specialist building surveyors.
The building survey therefore has to be delegated to
experts. These experts know their craft but may not have
sufficient knowledge concerning planning requirements or
be able to identify specific problem areas.
The survey is seldom extended with specific more detailed
information during the planning and renovation process.
Once the specialist surveyors are finished the survey is seen
as completed. In addition, planners and researchers do not
have the necessary skills to extend the existing survey in the
same way.
2.3 Laser-Scanning
Laser-scanning is a special technique associated with reflector
less tacheometry in which an object or part of a building is
scanned resulting in a high-resolution ‘cloud’ of points. The
disadvantages of the system are similar to those of reflector-less
tacheometry with some notable additions: Laser-scanning
results in a high-resolution description of a surface geometry
from which building-relevant parameters have to be deciphered
in a second-step. This post-modelling is still in the
developmental stage so that laser-scanning is not practical for
building surveying at present. In a later section we will come
back to a special application for laser-scanning in the surveying
of building detail.
2.4 Photogrammetry
Photogrammetry using stereo-image or multi-image
photogrammetry is rarely used for most building surveying
projects, primarily due to its high cost, the need for specialists
and the post-processing requirements for its assessment. In
principle stereo-image photogrammetry is suited for measuring
the geometry of irregularly structured building details.
The rectification of single-image photogrammetric results is
suited for surveying building surfaces. It is a quick means of
measuring a large amount of geometric correct information at
high-resolution. Rectification does, however, have limitations
when measuring irregularly structured surfaces. Developments
in conjunction with laser-scanning approaches are still in the
early prototypical stage.
All photogrammetric approaches require a direct visual contact
between the camera and the area to be measured. Areas which
are covered up or surfaces which fold back on themselves
cannot be measured.
As with tacheometry, the direct tactile contact to the building is
lost. Where cameras with insufficient resolution are used, object
information within the image may not be recognisable.
We can conclude that geodesic or photogrammetric approaches
are well-suited for establishing an initial survey. These can be
used to develop an overall geometric model and to provide an
geometrically-corrected basis for basic charting requirements.
Its most important contribution to the building survey is the
provision of a high-level geometric reference system to which
all further geometric measurements can be related.
3. DEFICITS
The examination of the characteristics of traditional and
conventional measuring approaches show that they have no or
only limited suitability for the supplementary measurement of
small-scale details. A whole area of surveying remains
unaddressed, which at present is covered by supplementary
sketches, direct modelling (profile measure, plasticine etc.) or
more complex measurement using string, plumb-line and
measuring stick. These traditional manual techniques also have
particular disadvantages:
Sketches only provide geometric information where the
drawing has been annotated with geometric measurements.
Supplementary sketches cannot be integrated as geometric
data in the digital building model. They can be used as a
descriptive attribute attached to a particular building
element.
The exact spatial location of the measured information
cannot be determined.
These disadvantages are most noticeable in the surveying of
details such as profiles, capitals and other complex and non
standard building elements (windows, doors etc.). A reliable on
site survey of each individual situation is fundamentally
important for the assessment of building renovation works, for
instance for the repair, extension or reproduction of building
elements and details. Ornate building elements, often made of
multiple elements are particularly common in the renovation
and conservation of historic buildings and are difficult to survey
using traditional approaches.
4. NEW TECHNIQUES FOR BUILDING SURVEYING
This gap in the coverage of geometric building surveying can
be addressed by tactile surveying methods adapted to the
requirements of existing buildings (Fig. 1).
Figure 1: Tactile building surveying
Manual building surveying methods can play a significant role
in conjunction with modern tactile surveying tools.
4.1 The integration of tactile approaches in a system for
building surveying
Before individual approaches can be examined in detail, tactile
surveying methods need to be integrated into the overall
surveying approach. The integration of tactile approaches into
