- 112 - 
the facades is not sufficient. Laser scanning provides a fast and 
easy way to get a detailed model of the surface for the creation 
of orthophotos. 
3.3 Cenotaph 
The cenotaph (empty tomb) of Emperor Maximilian I. is 
situated in the Hofkirche church in Innsbruck, Austria. It was 
created by various artists during the 16 th century and is known 
as the largest and most important mausoleum of the Western 
World. The sarcophagus itself (2.5 x 4.5 x 2.0 metres) is made 
of black marble and bronze. It is ornamented with 24 finely 
carved alabaster reliefs (80 x 50 cm 2 ) depicting scenes of 
Maximilian's life. A life-size bronze statue of the emperor is 
kneeling on top of the sarcophagus as well as four smaller 
bronze statues (the four cardinal virtues), which are situated 
near the comers. 
The first restoration attempt since the completion of the 
cenotaph (around 1568) started in January 2001 and is still in 
progress. During May 2002 there was a one-week break 
between two phases of restoration where the cenotaph was 
freely accessible, without any lattice or glass, for the first time 
ever. It had to be made the most of these few days by 
documenting this unique cultural heritage with state-of-the-art 
technology, before the cenotaph was hidden behind lattice and 
glass again, probably for the next 500 years. 
Figure 4. Left: Cenotaph in the Hofkirche church of Innsbruck. 
(Photo: AEIOU) Right: Uncovered sarcophagus with 
reliefs 
Measurements: In addition to traditional close range 
photogrammetry, carried out by an Austrian company 
specialised on this matter, i3mainz was engaged to record the 
cenotaph’s shape with laser scanning methods. For this purpose 
two scanners were used. The idea was to use the Mensi SOISIC 
scanner to record the plain geometry, including marble parts 
(steps, frame and lid) and bronze statues. Scanning the alabaster 
reliefs with details smaller than one millimetre by using this 
scanner is not sensible. Instead, the GOM ATOS II scanner was 
brought into action. 
A common coordinate system had to be created for the three 
measurements (photogrammetry, Mensi, GOM). Therefore, 
tacheometric measurements were carried out. Twenty special 
red spheres were placed on the cenotaph as connecting points to 
register the single point clouds from each scanner viewpoint. 
The spheres were measured by aiming at the left, right and 
upper contour and calculating the direction to the centre (the 
lower margins could not be measured due to the spheres’ bases). 
The photogrammetrists placed their adhesive reflecting targets 
on the cenotaph. Eight observation points for the total station 
were selected around the cenotaph. After measuring angles to 
all targets (observation points, spheres, photogrammetric 
targets) and using a calibrated invar rod as a scale, a common 
net adjustment was computed, which resulted in 3D coordinates 
with a standard deviation of less than 0.5 mm. 
Problems: In the planning phase of the measurements it was 
not clear, to what extent the material and colour of the object 
would influence the results of scanning. It was considered to 
spray the crucial parts with some kind of chalk or powder. The 
best conditions for both scanners, Mensi and GOM, are a dark 
environment and an object surface, which is bright and smooth. 
On site first the black parts of the cenotaph (marbled frame) and 
the bronze statues were tested with the Mensi scanner - with 
acceptable results. Some points were missed, but altogether the 
scanner worked very well as long as the sun was not shining 
directly onto the object. The GOM scanner had more problems 
with daylight and the black surface. The projected light pattern 
was completely absorbed by the marble, but the alabaster reliefs 
could be scanned properly, of course. 
Scanning with Mensi SOISIC: The whole cenotaph was 
scanned with an average point width of 2 mm. For each pair of 
reliefs one scan was applied including the neighboured parts of 
the black marbled frame and the steps below the sarcophagus. 
By using this method, the important parts of the marbled frame 
were always scanned from two directions which leads to less 
hidden areas. Moreover, the scanner was placed on a scaffold to 
scan the upper part of the cenotaph with the lid and the five 
statues. Each scan contained at least four spheres for 
registration. All in all, 20 scans were applied during four days 
and nights. One single scan took up to six hours (3-4 hours as 
an average) depending on the size of the scanned area. 
Figure 5 shows the registered point cloud of the whole ceno 
taph. Altogether, more than 10 million points were recorded, 
which is a large amount of data even for powerful PC’s. 
Figure 5. Registered point cloud of the cenotaph (shaded view) 
Scanning with GOM ATOS II: Scanning the reliefs with 
ATOS II turned out more difficult than originally expected. To 
reach a maximum of accuracy and detail, the scanning volume 
has to be very small. In order to maximise the precision of the 
model, the reliefs had to be divided into several tiles - each part 
had to be scanned separately. This was possible by sticking 
special reflecting targets to the object and using those to stitch