Geography Reference
In-Depth Information
based laser scanner records the tridimensional points by measuring the vertical and
horizontal angles, as well as the distance to each point. Even though there are largely
different technologies, the field-use of the 3D scanner uses elements of the work
methodology of the total station. In case the morphology of the scanned object is complex,
more than one station points will be used. Thus, all its surfaces will be scanned. In case the
shadowed surfaces are not reached by the laser beam, the software captures such areas
automatically then integrates them to the scanned object. The process relies on registering
distances and angles, and the data thus produced is used to compute the points' coordinates.
The ability to register a massive amount of 3-D information in a relatively short time is the
main advantage of this instrument, in contrast with classical equipment such as the total
station [24, 10].
The methodology used for the analysis of Cucuteni Ravine is strongly influenced by its
impressive size and the local topography, which required, in the end, the use of 17 station
points. To merge the 17 positions, 6 reflective tie-points (Figure 6) were used for each of
them, except for the last one. Nevertheless, for the entire model we used 24 tie-points, since
some of the scanning positions were referenced to tie-points also used by other station
points, where the physical distance allowed. Terrestrial laser scanning (TLS) generates
several point clouds, with local coordinates and additional info (the light intensity in the
reflected beam, and the RGB values obtained from an external or internal photographic
camera). The point clouds, after having been registered from different positions, must be
merged as to obtain a complete model of the scanned target. This procedure is called
"registration" and involves merging the point clouds through the use of reflective tie-points,
specially built and delivered by the manufacturer, which are automatically recognized by
the scanner when a very fine scan is performed.
Figure 6.
The round target used as tie-point
For the current project, in all of the three scanning sessions, we employed a Leica
ScanStation HDS 3600 3D scanner. It is a time-of-flight active scanner, which works by
timing the round-trip time of a pulse of light. The operation range is 270º horizontally and
360º vertically (Figure 7), and the active distance is 300 m. With a resolution of 6 mm at a
distance of 50 m, and due to its ability to register approximately 2000 points per second, the
ScanStation HDS scanner is among the most effective equipment of its type. The average
resolution for all of the scans was of approximately 6 mm, and the registered points
numbered millions, despite the fact that the majority of positions overlapped. Although an
