2011 - Geoinformatics

A r t i c l e
Point Clouds and Multi-image Panoramas
Surveying Buildings
The development of building knowledge systems is nowadays a meaningful step when planning
architectural maintenance and managing emergencies during a building’s life cycle. A 3D photo-textured
model, which can describe both spatial connections and material properties, is a measurable
virtual object that is achieved via terrestrial survey techniques, such as laser scanning and imaging.
This article presents the current status of techniques and technologies for the construction of a textured
model, through the support of experiences regarding an ancient historical building in the Lombardy
region of Northern Italy.
By Luigi Colombo and Barbara Marana
Fig. 1- The Monte Oliveto Sanctuary, suggestively placed inside a small valley
Knowledge technologies
Survey and representation techniques can provide, without contact,
spatial numeric plots and drawings with an assigned precision, to
produce a geo-database of architectural information.
The survey process can be enhanced using image measurement (close
range photogrammetry) or scanning laser sensors, which record a
sequence of spatial points describing the selected object. Usually, the
combination of both methodologies will overcome accessibility and
visibility problems, which often affect the employment of optical instruments
during a terrestrial survey.
Photogrammetry is based on the use of an imaging camera (film or
digital), in which the acquisition of many overlapping images produces
spatial and orthographic representations, thanks to the application
of projective geometry algorithms. Photo gram metric solutions,
despite offering interesting and complete application fields, do not
permit simultaneous processing with acquisition. This said, it is now
in competition with the emerging laser scanning technology, which
provides real-time, fast, and increased automatic metric output.
A sophisticated digital sensor, placed over a standard support, is
used to emit a thin laser beam towards the object to be measured.
The beam, while rotating in the horizontal and vertical planes,
describes pre-selected areas, directly recording a cloud of spatial
points (coordinates x, y, z). The reflected energy and, under certain
circumstances, the photographic information, produces an object
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Fig. 2 – The church interiors, with Z+F scanner at work and mobile targets
point model of given density with materials and natural colours.
As with photogrammetric methodology, the laser device is located at different
spatial positions providing overlapping cloud sequences in order to
guarantee software connection in a global model.
It is interesting to note that this motorized sensor can record up to
1,000,000 object points per second, with an accuracy of a few millimetres,
and within a range of more than one hundred metres.
October/November 2011