The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
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Figure 3. Example of a coloured point cloud of building 
facades at the Historic Peninsula 
80ha of the project area (of in total 1500ha) could be scanned 
within the first six months using the existing production 
capacity, which clearly indicated, that the scanning would need 
more than eight years for the entire area of the project, if this 
current scan rate of approximately 0.7ha per day could not be 
increased. It was obvious that the project deadline could not be 
met; therefore it was decided to increase the production rate by 
the integration of a mobile system. 
Figure 4. Sensor configuration on the mobile mapping van of 
VISIMIND AB 
4.2 Mobile terrestrial laser scanning 
As a consequence the scan progress was significantly increased 
by the introduction of a mobile mapping van from the Swedish 
company VISIMIND AB (Figure 4) in June 2007 using a 
hybrid sensor system on the vehicle consisting of a terrestrial 
laser scanning system HDS4500, supported by GPS/IMU and 
digital cameras. The sensor integration and the calibration of 
the system in the streets of Istanbul took some weeks, but the 
data acquisition in the field was working by the end of June 
2007. The laser scanner’s orientation was fixed in the horizontal 
direction, scanning only in the profile perpendicular to the 
direction of movement of the vehicle. It has been operated with 
25 scan profiles/second, later improved to a speed of up to 40 
profiles/second (possible maximum by instrument specification: 
50 profiles/second). The distance between neighbouring profiles 
was 2-3cm in the beginning, corresponding to a van speed 
during scanning of 0.5m/sec up to 0.75m/sec or 1.8 km/h up to 
2.7km/h. 
Figure 5. Distribution of control points in the streets for mobile 
terrestrial laser scanning (left), and destroyed target (right) 
Due to problems with the reception of the GPS signal in the 
narrow streets of the Historic Peninsula control points were 
marked on the buildings every five meters along each side of 
the street (Figure 5). Some targets were removed or destroyed 
before scanning (Figure 5 right) and were replaced by natural 
points such as window comers. Some targets have been 
destroyed after scanning, but before the geodetic determination 
of the object coordinates, they also had to be replaced by 
natural points. The sticking on of the targets was carried out by 
BIMTAS staff (4-5 people), while the determination of the 
target coordinates was performed by BIMTAS staff and 
additional subcontractors. BIMTAS staff measured additional 
natural ground control points, well distributed on the facades, in 
order to stabilise the in-house data processing of the mobile 
mapping system, while the subcontractors only measured the 
targets. Not all control points have been identified correctly in 
the point clouds causing geometrical problems for the direct 
geo-referencing and some geometric deformation of the point 
clouds (Figure 6: misfit at block comers, swinging building 
façade, etc.). Nevertheless, the technical parameters of the 
hybrid systems were optimised on the job due to these problems 
with the quality of the pre-processed point clouds. 
Figure 6. Geometric problems from direct geo-referencing of 
point clouds (from left to right: swinging façade, misfit at block 
comer, and deformation of a façade) 
For problematic facades where control points were missing, 
VISIMIND recently developed with the so called ‘image 
tracking tool’ an automatic photogrammetric bundle adjustment 
enabling a bridging of longer distances without control points 
Figure 7). 
Figure 7. Image tracking tool for “problematic” facades 
without control points