4.4 Multi-Sensor and Multi-Scale
Approach
Among the various obstacles encountered in
generating the highly detailed 3D model, the difficult
survey conditions significantly impacted the
processing time. Indeed, the noise in the cloud caused
by many pedestrians in the survey area (winter
tourism peak) has been solved through a time-
consuming manual intervention on the point clouds.
The orientation of the data within the same reference
system is the basis for a correct data fusion.
Consequently, a thorough and extensive topographic
survey proved to be fundamental for data integration
and evaluation.
Regarding the partially shaded facades of tall
buildings in narrow streets, the data acquisition was
planned so that the illumination conditions were
consistent throughout the model. However, the
photogrammetric information from those areas is
sparser due to the distortions generated when very tall
(or long) elements are captured up close by an optical
sensor. The reconstruction of the texture of the
narrow streets was possible thanks to the spherical
camera (Ricoh). In this regard, in line with the
considerations of other authors, the results of this
work demonstrate the complexity of the choice of
sensors that requires knowledge about the operability
of sensors in terms of resolutions, characteristics, and
behaviour in specific operational fields. Thus, the
analyst's role in identifying the correct combination
of sensors according to the requested level of detail is
crucial. When adequately planned, integrated
approaches are successful solutions for constructing
highly detailed 3D virtual models thanks to their
customizability in terms of time, costs, and sensors.
Through a careful combination of sensors and
algorithms, final products with specific levels of
detail can be obtained.
5
CONCLUSIONS
In this work, a 3D model of part of the historical
centre of Turin was generated at a very high
resolution to be used in different domains. Indeed, it
is (i) the base for the design of a new station of the
metro line, (ii) a digital memory of the square, and
(iii) the database for a virtual reality model. The
proposed LiDAR and SfM-MVS integrated approach
to build a highly detailed 3D virtual model can be
replicated in other urban and natural environments.
However, although highly detailed 3D modelling is
becoming more and more widespread, there are still
no general standard procedures for their generation.
The geomatic community is moving to fill this gap.
This work represents a step towards the
standardization of operations. It emphasizes the
importance of integrating geomatic techniques, but
further studies on replicability in disparate urban
environments must be investigated.
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