quality control, reverse engineering and rapid prototyping for 
small objects. 
Figure 1. Scanners: Mensi S25 (top left), Cyrax 2500 (top 
right), GOM ATOS II (below) 
3. PROJECTS 
3.1 Caves 
The survey and documentation of underground cave systems is 
a big challenge for conventional measurement methods. Due to 
the irregular shape of caves, laser scanning might be a proper 
technique to record them. i3mainz had the possibility to test the 
potential of laser scanning at the volcanic caves in the Eastern 
Eifel. There, in the Middle Ages, humans started to mine the 
basalt below the lava flows of the Wingertsberg volcano which 
erupted 200,000 years ago. The result was a huge system of 
underground caves. The Cyrax scanner was used for a demo 
project. The Cyrax scanner was selected, due to its good 
accuracy at distances of 10 to 20 meters and above. A 
disadvantage was the relatively small field of view (40° x 40°). 
For smaller caves it might be sensible to use the Mensi scanner 
instead, because it is capable of scanning a larger area of the 
cave in one scan (320° x 46°). 
It should be noted that the Cyrax scanner is able to work up to 
eight hours by using two 12V batteries, while the Mensi scanner 
is dependent on permanent AC power supply. This makes the 
Cyrax scanner much more flexible, considering that the 
operation of the Mensi scanner with a power generator is not 
possible within a cave. 
Figure 2 shows a model of the scanned part of the cave. Five 
viewpoints were used in this case. To connect the single scans, 
small spheres were placed at different positions and used as 
connecting points for the registration process. A medium point 
grid of 5 cm was chosen which was by far sufficient to 
document the cave’s geometry. At the end the scan data was 
reduced to 25 % with the simplification software Qslim. 
The main difficulty during scanning was, not to miss hidden 
areas. The cave was quite full of comers and pillars, so a lot of 
viewpoints are needed to capture all the surfaces without 
missing parts. Nevertheless, laser scanning appears to be the 
only useful method to document the complex geometry of a 
cave or a cave system. It is still a lot of work, but there is no 
other measurement technique that produces such detailed data 
within a comparable amount of time. 
Additional tacheometrie measurements for the spheres have to 
be used to determine a horizontal reference plane and a common 
coordinate system. 
Figure 2. Polygonal model of the scanned cave 
3.2 Church ruin 
Another interesting application of laser scanning is the creation 
of digital surface models of architectural facades. i3mainz is 
working on a project with the intention to document the stages 
of construction of an old church which is remaining as a min. 
Close range photogrammetry was used to extract the stones’ 
contours. Additionally, orthophotos had to be created. For this 
purpose, the facades were scanned with both the Mensi and 
Cyrax scanner. Since there was little space inside the church, 
the Mensi scanner with its 320° vertical field of view was used 
for the interior facades. Outside, the Cyrax could be used to 
scan a whole facade from a larger distance in one scan and 
under daylight conditions. 
The point cloud of each facade was the basis to create first a 
regular lattice and then a DOM (digital object model) as input 
data for the creation of an orthophoto. The point cloud of the 
scanner was transformed to thè global system by using identical 
points (edges of windows, projecting stones etc.). 
Figure 3. Polygonal model as a basis for an orthophoto 
This project, too, can be seen as an ideal application for laser 
scanners. Often, a simple rectification of the photos taken from 
- 111 -