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Title
New perspectives to save cultural heritage
Author
Altan, M. Orhan

C/PA 2003 XIX"' International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
Based on the very dense point clouds provided by laser
scanners, the DSM can be derived directly from the laser
scanner data (Wehr & Wiedemann 1999). If 3D vector data is
available from tacheometry or photogrammetry it is usually
necessary to derive a 3D boundary representation CAD-model
as an intermediate product (Wiedemann 1996). This additional
step is time consuming and may lead to additional errors. Based
on these experiences a new strategy has been developed: That is
to derive the DSM from intelligent tacheometrie measurements,
which are to be acquired in an optimized manner.
At the moment the software works with Leica total stations of
the TRCM and TCRA types of the 1100 series. The program
FAMES for the Façade Measurements uses the GEOCOM
interface to control the total stations.
Figure 3. Total station Leica TCRA 1103
2. GENERATION OF DIGITAL ORTHOIMAGES
2.1 Project Preparation
The first step is the same for all serious documentation projects:
The establishment of a site covering reference systems. For this
purpose the system Archimedes3D provides a geodetic network
adjustment. Signalized and natural control points are measured
manually.
2.2 Manual Measurements
The next step is the generation of Digital Surface Models of the
facades. For this purpose Archimedes3D controls the motorized
total station. The process starts with the manual measurements
at the facade, providing the system with the approximate extent
of the object and lines and areas of special interest. The lines of
special interest are vertical and horizontal profiles over the
whole object or parts like cornices and window borders. Areas
of special interest are reliefs or other decorative elements.
2.3 Autonomous Measurements
After this definition phase, the system starts to determine the
exact extent of the object, to measure profiles and point rasters
in different regions in a predefined density.
The extents are located by stepping outward from the initial
border points until the measured distance is significantly bigger
than the initial distance or undefined. The last surface point is
located using a suitable approximation procedure.
The profiles are measured automatically in the predefined
horizontal or vertical profile plane (Juretzko 2002). They are
automatically densified by a process to locate discontinuities in
the profiles.
Due to the limited speed of the total station the acquired point
density is much smaller than that of laser scanners but can be
adapted to the actual requirements. The data rate is rather low
with about 1-3 seconds per point. Therefore the operator must
consider this data rate during the definition of the local raster
density.
Control Network Measurements
Measurement of Inita! Parameters
Autonomous Measurements
Preliminary DSM Generation
Additional Measurements
Final DSM Generation
Image Orientation
Differential Rectification
Figure 4. Data flow in Archimedes3D
2.4 DSM Generation
Starting with the overall profiles the data is used to produce a
Digital Surface Model of the facade. Gaps and discrepancies in
the DSM are located and closed by additional measurements.
This process is automatic and requires no manual interaction.
During this process, the operator can take pictures with the
digital camera. A lot of points and features are geodetically
measured. Therefore sufficient control information is available
to do a “calibration on the job”. To achieve a better geometric
stability it is recommended to restrain the quantity of interior
orientation data by avoiding zoom and auto focus. Tools to