statues)
hotos of
fact, it's
) model
2] size is
scanning
e with a
1at point
e digital
xd.
ie plane)
survey is
; way we
Nc and
used to
ing the
Marco in
ic entity
rpolating
Figure 1 and 2 want to expalin construction of an arch based on
n rectified points. If the distance between the points and the
interpolated arch is less than the graphic precision (0.2 mm x
scale of representation) the plotted entity becomes the
circumference.
Beading (cornices) of architraves and lintels is even more
evident, since they are parallel to the construction of the orders
(figure 3-4).
Figure 3: Errors in plotting
Figure 4: Correct orders plotting
From the photogrammetric plotting, we can see that the warping
is due to unavoidable rectification errors. We affirm that these
errors have a normal distribution and therefore, if a cornice has
been rectified with many points, it is more sensible to
interpolate the points to obtain a straight line that represents it.
Clearly this reasoning is valid in the case where there is no
breakage due to decay phenomena.
The laser can survey many points that are indifferent with
respect to the architecture: they belong to the object but are not
chosen by the operator who understands the rules of the
architectonic composition (like architectonic orders). (Figure 5)
The problem with survey done with laser technology is
obtaining an architectonic representation starting with those
points.
atas
iet
ains
Figure 5: Points cloud for the survey of the main facade of the
Stazione Centrale in Milan
Currently, many work groups are working on trimming down
the points cloud, eliminating the noise to reconstruct the
surfaces.
The work done by the authors is mainly addressed to obtaining
an immediate result: generation of orthophotos using the cloud
of laser points for creating DEM and the same laser points
appropriately chosen because of the orientation with the DLT of
the photograms taken with digital, non-metric cameras.
For the DEM, diverse algorithms have been tested which have
all shown various constraints due to the complex configuration
of the architectonic surfaces.
In fact, unless uniform brickwork is surveyed (for which the use
of lasers would be useless) architecture shows discontinuity due
to the volumetry of the structure and the presence of accessories
and ornaments.
It is therefore particularly difficult to generate mesh
automatically without preliminarily treating the clouds. These
processing include identification of the subset points that
logically belong to a compositional part of the architecture, as
one understand when thinking about a wall, a column, a vault or
a parapet.
—303—