CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
network, the availability of imaging cameras which can work in 
combination with the scanner, weight and ease of transpor 
tation, power supply (battery operation), availability and quality 
of software. 
Besides, the quality of the user support and the guarantee 
conditions are not the same for all producers. These should be 
checked carefully in addition to the technical specifications 
before a decision is made to favor one product or another. 
3. TESTING INSTALLATIONS AT i3mainz 
3.1 General remarks 
When the decision was made to start a research program with 
the aim to compare the accuracy and performance of different 
types of laser scanners, new testing installations had to be 
developed. In order to reduce measuring time and expenses, a 
set of targets was designed using standard materials, and all 
experiments were installed in two buildings of FH Mainz, 
University of Applied Sciences. Most experiments can be 
repeated at any other location provided the same type of targets 
and surface paints are used. 
Since single points of scans cannot be analyzed and compared, 
ball type targets (white spheres with a diameter of 76.2 mm on a 
magnetic ground plate as produced by MENSI) are used for 
most distance determinations, and plane boards for experiments 
concerning range noise and investigations concerning the be 
havior of surfaces with different reflectivities. Some additional 
special objects, described below, were constructed for further 
investigations. 
It should be noted that these arrangements do not allow to find 
the mechanical, optical or electronic sources of errors in the 
instruments; instead they show the effects of such an error on a 
certain measurement under practical measurement conditions. 
When, for example, a distance between two spheres which are 
at the same distance from the scanner, is derived after their 
center points have been modeled from the point clouds, this will 
give a general indication of the angular accuracy of the scanner 
but does not really tell everything about the accuracy of the 
angular position of a single point. This is basically the same 
approach recommended by VDI/VDE in their guideline (VDI/ 
VDE, 2002). Since the same procedures and targets were used 
for all instruments examined, this provides a reliable method to 
compare the performance of these instruments under practical 
application conditions. 
3.2 Angular accuracy 
Errors in the angles between two rays can be detected when the 
distance between two spheres located at equal distances from 
the scanner is determined. Modeling the spheres will result in a 
low pass filtering. Therefore the results will not allow detecting 
small arbitrary angular variations. 
Fig. 1; Box for positioning spheres at defined locations on steps 
A first test installation uses white spheres in a box that can be 
positioned at well defined points on a stone stairway at the end 
of a 60 m corridor. The box (fig. 1) allows repositioning the 
spheres within some tenths of millimeters with respect to the 
stone steps when the tips of six bolts protruding from the 
bottom and the sides are brought in contact with the stone faces 
of the steps. Thus, the precise position, acquired with geodetic 
methods can be re-established any time. The targets are used on 
either side of six steps at a distance of about 1 m (fig. 2). This 
allows the calculation of six independent short distances in 
horizontal and six in vertical direction. 
Fig. 3: Steel plate for positioning sphere at a wall 
In a different room, four spheres are installed at a vertical wall 
at the corners of a rectangle 3.5 m high and 5 m wide. Since 
special steel plates with two defined mechanical contacts for the 
magnetic ground plates of the spheres are used (fig. 3), the 
spheres can be re-positioned precisely to the original position 
which was determined by geodetic methods. This arrangement 
is scanned from a distance of up to 15 m from three observation 
points as indicated in figure 4. This again yields six independent 
distances in horizontal and six in vertical direction which can be 
compared to their calibrated values. 
Fig. 4: Location of spheres at a wall and observation stations 
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