MULTI-RESOLUTION MODELLING FROM MULTIPLE RANGE VIEWS:
THE LASER SCANNER SURVEY OF PORTA PORTELLO, PADUA, ITALY
G. Salemi *, F. Liberi? , S. Mischi?, V. Achilli *, G. Artese"
* Dipartimento di Architettura, Urbanistica e Rilevamento — Facoltà di Ingegneria, Università di Padova
Via Marzolo, 9 — 35131 Padova — Italy - giuseppe.salemi@unipd.it
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Dipartimento di Pianificazione Territoriale, Università della Calabria, Cosenza - Italy — g.artese(@unical.it
Commission V - WG V/2
KEY WORDS: Laser scanning, Point cloud, Nurbs, Mesh, Resolution
ABSTRACT:
In this paper, the authors present an experiment performed in Padua, Italy to model a cultural heritage object from multiple range
views. This object is Porta Portello, an old monumental door near the University, and has been scanned using the laser scanner
Cyrax 2500 from Cyra Technologies. A multi-resolution approach was carried out: 1 cm and 2 cm grids were used to acquire laser
data for the front and the back sides; instead, 0.5 cm grid was used to acquire more detailed scenes of some artistic features. A
| typical approach is based on the closest point caching to minimize the computational resources. In order to develop an unique multi-
resolution model, two registration techniques were taken in account: the point-to-point alignment and the point-plane alignment.
First of all, the pair-wise registration has been performed using some high resolution range views. After this phase, a global
registration was produced using all the 11.000.000 of the acquired cloud points. Some patches were also used to minimize the noise
of the acquired data, when “moving” objects have been scanned together the “stable” surfaces. Furthermore, the LOD (Level Of
Detail) approach was used to simplify the 3D scenes to reach a good compromise among accuracy, topology and data decimation.
1. 1. INTRODUCTION
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The cultural heritage documentation is today well performed
using the laser scanner methodology. In Padua (Italy) there is
an old monumental door (Figure 1) near the University, which
was scanned using the Cyrax 2500 from Cyra Technologies.
The main goal was the multiresolution documentation of this
historical access door (Figure 2) using lcm, 2em and 0.5 cm
grids acquired from multiple range views for, respectively, the
front side, the back side and some artistic scenes like the Venice
lion and a castle (Figures 4 and 5).
The regular and irregular surfaces were worked at long-range,
medium-range and close-range scale.
Figure 2. A. Canal called Canaletto,
*Porta Portello e la Brenta a Padova", (1735-40),
National Gallery of Art, Washington DC.
2. MONOGRAPHY
The data collection is very large, including 6 Scanworld with a
total number of 30 scans ranging from 45000 up to 2 millions of
acquired points for each scan. The acquisition time is, of
course, related to the previous dimensions and it ranges from 4
to 38 minutes. The Cyra targets have been also acquired using a
48 x 48 matrix with 1444 points in about 1 minute from a 25 m
distance.
All this data has been organized in a special monography,
where some kinds of metadata related to each scan are
provided; of course, all the data useful for the final registration
are included.
An example of monography is reported in Figure 3, where is
included the ID of scan in the designed Scanworld, the
planimetry of the area with the field of view (yellow), the
digital image of the scene. In the same “space” a table is added
which includes the scan Id, the distance from the laser to the
object, the grid resolution, the acquisition matrix dimensions,
the number of acquired points and the required acquisition time.
Figure 1. Porta Portello, Padua.
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