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Sampling axially symmetric solids, like vases, cups etc. which
should be described as volumes may be digitize by mounting
the object on turntable and using a vertical line scan (s.
Figure 3). After each line scan the turntable is moved by a
defined angular step. Turntable and 3D-LS are controlled by the
same computer. The setup turntable and laser scanner must be
well calibrated as well as the exact orientation between the
coordinate systems of the turntable and the laser scanner must
be known.
When scanning extended concave surfaces across a hemisphere
like vaults or interiors of rooms, a setup depicted in Figure 4 is
of advantage. Here the 3D-LS is mounted on a turntable and a
vertical line scan is applied. After each line scan the turntable is
Figure 5. Scanning Interior Rooms (one belt)
moved by a certain angular step in azimuth. After a turn of 360°
a belt with a vertical FOV of 30° is sampled (s. Figure 5). To
obtain a hemispherical coverage the 3D-LS must be moved in
elevation. This is carried out by an additional stepping motor
drive (s. Figure 4). For nadir an image scan is advisable. These
selected examples make clear that the optimum scanning
pattern is very dependent on the applications and commercially
available laser scanners are limited to one scanning pattern
realized by optimally designed opto-mechanically setup; e.g.
the Cyrax 2500 of the company CYRA features a two-
dimensional line scan where as the LMS-Z210 of the RIEGL
company carries out a vertical line scan. The 3D-LS of the INS
was developed for scientific studies, to derive critical design
parameters for the optimization of future laser scanners and
measurement procedures.
Figure 6. Glass Head
neighboring caves were scanned with the setup shown in Figure
5. The rooms had a quadratic plan form of 7.2 m x 7.2 m. The
maximum height was 4.35 m. The vertical laser line comprises
40 measurement points. The 360° in azimuth were subdivided
in 500 steps. Seven belts were scanned with elevation angles of
0°, 9°, 22°, 36°, 49°, 63° and 76°. At the nadir a complete
image of 200x200 points were taken. One cave was surveyed in
1.5 hours. The data sets of both caves were sampled
independently. The data sets were merged using identical points
Figure 7. 3D-Projection of Caves
in both sets and adjustment methods. This was possible,
because the two rooms were connected by a door. Figure 7
shows a look from the outside. The survey comprises 360000
points.
3.3 Using the Imaging Scanning Pattern
3. SURVEYS WITH 3D-LS
With regard to the different scanner setups typical surveys will
be presented and discussed.
3.1 Object on a Turntable
Figure 6 shows the digitization result of a glass head. As the
scanner did not sample information on the top of the head the
solid was not surveyed comprehensively. However, most of the
object can be described by a well ordered point cloud directly
after the survey. This means the data were sampled volume
oriented.
Two typical examples for using the imaging scanning pattern
will be regarded. First a copy of a relief from the famous master
builder Schinkel with the dimensions width 80 cm, height
Figure 8. Relief
3.2 Digitizing of Rooms
In the historical "Maerzenbierkeller" in Polling, Bavaria
(Germany), which was built in 1745/46 by Michael Fischer, two
40 cm and depth 9 cm was scanned at the "Bauhof' in Berlin.
Germany. The relief exhibits some undercuts. Therefore, two
views must be taken with the 3D-LS. The final result of the