International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004
I )episodes in the lives of Joachim and Anna (1-6)
2)episodes in the Virgin Mary's life (7-13)
3)episodes recounting Christ's life and death
The lower parts of the walls contain a series of frescoes
illustrating Vices and Virtues in allegory.
Major restoration work was undertaken in the late 19th century
and again in the 1960s. More recently, damages due to
atmospheric pollution, caused the painted surfaces to crumble
away. Urgent restoration was carried out immediately and, on
May 31 2000, a special technical installation was set up, a sort
of "artificial lung". This special air-conditioned environment
now both purifies the air inside the Chapel and monitors its
atmosphere continuously, in order to protect these unique
frescoes, some of the most important of all time.
3. LASER SENSORS
Recalling that the initial idea was to generate and compare 3D
models of the church from different range data sets, four
ground-based laser scanners were employed for this work:
Riegl LMS-Z210, Mensi GS 100, Optech ILRIS 3D and Cyrax
2500. Each of this sensor features different performance in
terms of acquisition speed, depth accuracy, maximum distance,
point cloud resolution, noise, etc. A summary of their
characteristics is reported in tables 1 and 2.
All the scans were acquired at night after visiting hours to be
able to place the sensors in the more appropriate positions
inside the church. Surveys were performed in different times,
according with the availability of the laser scanner from the
dealers and with the different data acquisition speeds provided
by the laser scanners: altogether, all the data were collected in
one week.
As previously mentioned, the whole church could not be
completely surveyed using only one laser sensor, therefore we
generated a unique 3D model composed of patches of the
collected scans, namely: about 70% of range data arc from
Mensi, 15% from Cyrax, 10% from Ricgl and 5% from
Optech.
A more detailed description about the distribution and the
quality of these range data will be the topic of the next section.
Table 1. Mensi and Riegl laser scanner specifications
MANUFACTURER MENSI Riegl USA
PRODUCT MENSI GS100 LAS 22108
PERFORMANCE
Laser Wavelength (in nm) 532 904
Laser Power (in W, mW) | mW imu
FDA Laser Classification (Class) 2 (18 sanded 3 SRE) i
Beam Diameter at Specified Distance : eL
f imm at 50m 50 rm at Sí m
(0.Y ft at X ft/Ymm at X m)
Measurement Technique Time-ob flight UDAR
Average Data Acquisition Rate (pps) 5,000 8.000
Maximum Data Acquisition Rate (pps) 5,000 12,000
Distance Accuracy at Specified Distance | 2.2 mm at 50m/
(OY ftat X ft;Ymm at X m)
Position Accuracy at Specified Distance | 3.2 mm at 50 m/
(0.Y ft at X f/Ymm at X m)
AD
15 mm at 400m
5 mum at HOO m
7
6 mm at 1600 m
5 mon at LOO m
Angular Accuracy 6.5 seconds 7.2 secands
Minimum Range (feet/m) im 4m
Maximum Range (feet/m) Up ta 150 m [1] 500m
Field of View {vertical angle) 50° 80
Field of View (horizontal angle) 260° 360
GENERAL
Scanner Dimensions (LXWxH) 34527 £42 cm 44 x 21
Scanner Weight (pounds/kg) 156 kg 13
Internationa
feral
Table 2.
['MANUFACTL
PRODUCT
| PERFORMAN
Laser Power
FDA Laser CI:
Beam Diame
(0.Y ft at X
Measuremen
Average Date
‚Maximum De
Distance Accı
(0.Y ft at X
Position Acct
(o.Y ft at X
Angular Accu
Minimum Ra
Maximum Ra
Field of View
Field of View
GENERAL
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