Geography Reference
In-Depth Information
external photographic camera can be attached to the scanner, we thought it to be no better
suited for the task than the internal camera [86].
Figure 7.
The visual field of the scanner
A particularly important phase of the fieldwork facet of the project was the geo-referencing
of the point clouds. Using a reference station positioned on fixed known spot and a Leica
1200 GPS receiver, we referenced the point cloud established as the basis for the 3D model
to the national coordinates system (Stereographic 1970). In fact, our methodology was
based, for all of the three sessions, on computing the differences between the obtained geo-
referenced models using CAD and GIS. In respect to the raw data processing, it was carried
out by filtering the data using the Cyclone dedicated software program, registering the data
(see above), reducing the point cloud, creating a mesh by triangulation, and texturing the
model. The final results of the analysis were produced by exporting sections, transverse and
longitudinal, of the three tridimensional models obtained in each session.
As a case study, the selection of the Cucuteni-Baiceni Ravine for the present paper was
based on its high level of activity and its lack of arboreal vegetation, which could have
partially impeded the measuring of the volumetric parameters. The undergrowth vegetation
had then to be erased using the technical methods allowed by the software. Furthermore, for
increased accuracy, the edge of the gully was outlined during each session by using the two
"traditional" instruments mentioned above (the reference station and the 1200 GPS receiver,
both produced by Leica). The operation was somewhat cumbersome, because in such cases
the data must be collected from extremely numerous positions, as to take into account all of
the inflexions [44, 10]. All of the positions were geo-referenced and corroborated with older
measurements. In this way, we were able to estimate the rate of soil erosion in the gully, for
each of the measurements taken. The conjoint use of these two types of measurements (GPS
and 3D scanner) means that the risk of error was much diminished.
Another stage worth mentioning is, in the lab phase of the project, the filtering and
modeling of data, to the aim of producing results compatible with the complementary
software we used (CAD, GIS). Data filtering is a compulsory stage of the analysis, as the
vegetation present at the scanning site, together with the very large amount of data, could
result in errors in the Digital Terrain Model export-for-GIS process, as well as during the
