CIPA 2003 XIX th International Symposium, 30 September-04 October, 2003, Antalya, Turkey 
the system is important as all tactile tools have the following 
common characteristics: 
high precision, 
low reach, 
often realised under laboratory conditions. 
All tactile approaches when used in isolation are unable to 
measure overall high-level geometric information, and are 
therefore unable to position building elements with the 
necessary precision within the overall geometric survey. Instead 
they refer to their own system of reference provided by 
transmitters and receivers located close to the object to be 
surveyed. 
The absolute positioning of measurements from the tactile 
system in the overall geometric system can be achieved by 
transforming the local relational co-ordinate system to the 
overall system as provided by the initial survey. Key points can 
be measured which already exist in the overall geometric 
building model. These are typically the corners of rooms, 
window or door jambs, all points which the tactile measuring 
systems can also measure. Fig. 2 describes the process of 
integration within the overall system. 
The process corresponds to classic free stationing in geodesic 
applications. The transformation of the local system to the 
overall system should be realised so that the high-precision of 
the detail measurements from the tactile sensors are not 
distorted by the less accurate positioning of key-coordinates 
from the overall reference system (corners of rooms). 
Appropriate algorithms already exist in geodesic practice (see 
Niemeier, 2002) and can be applied equally to our 
requirements. With the help of appropriate software, the 
initialisation process of the measuring equipment in the overall 
coordinate system is fairly straightforward for the user. 
Figure 2: Free positioning of tactile sensors within the overall 
geometric reference system. 
4.2 Tactile Systems 
Tactile measurement systems can be adapted primarily from 
two other independent fields: Geometric controlling in 
mechanical engineering and positioning systems for VR/AR 
applications. We shall take a closer look at one system from 
each application area. 
Similar systems are also used to track persons within buildings 
(Schiele, 1999; 1GD, 2003). A variety of different principles are 
used but all of these are insufficiently accurate to be able to be 
used for surveying building detail. An independent 
development using a so-called Indoor GPS system using sound 
waves has been developed (Ziegler, 1995) but has never 
achieved practical use. 
There are three primary positioning systems which offer 
potential for surveying building detail: 
a) Optical systems 
Optical systems necessitate a direct visual contact between 
the tactile element and the local reference system. Some 
systems fulfil very high precision requirements (e.g. 
laserinterferometric approaches (Leica, 2003)) and all 
systems are sufficiently precise for surveying building 
detail. The next section describes two robust systems 
developed for mechanical engineering purposes (ProCam, 
2003) and for positioning VR-applications (HiBall-3100, 
2003 ). 
b) Electromagnetic systems 
Electromagnetic systems are often used for VR-applications 
(e.g. Polhemus, 2003) but are generally not suited for 
surveying building detail as they can be affected by metal in 
the building substance. 
c) Inertial systems 
Inertial systems (movement sensors) are very flexible as 
they do not depend upon external reference points. The 
sensor-drift which can occur means that it has to be used in 
conjunction with other sensors. Its application for building 
surveying needs to be examined in more detail. Some 
existing approaches include (Intersense, 2003). 
4.2.1 Optical System: HiBaIl-3100 
The HiBall-3100 tracking system (HiBall-3100, 2003) was 
developed for AR and VR applications. It has the following 
characteristics: 
Simple handling and setting up 
Low weight 
High precision achievable through high-frequency 
positioning 
Figure 3: HiBall-3100 optical Figure 4: HiBall-3100 Stylus 
sensor 
The system consists of an optical sensor with six lenses set up 
so that a 360° view is possible (Fig. 3). Infrared LEDs serve as 
reference markers in the working area. The use of a stylus with 
the HiBall-sensor means the system can be used as a tactile 
device for locating coordinates (Fig. 4). The HiBall-3100