International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
  
compute the position in a frequency of about 5 Hz. Depending 
on the geometry between the user and the set of satellites 
observed, an accuracy better than 5 cm can be achieved. For 
this study two Trimble 4800 GPS receivers have been used. The 
roving receiver outputs co-ordinates in a local co-ordinate 
system. In this case, they are transformed to Gauss-Kriiger co- 
ordinates. 
The orientation is measured by the inertial measurement unit 
(IMU) Xsens MT9 (www.xsens.com). The Xsens-IMU measures 
angular orientation of the sensor referring to an co-ordinate 
system defined by the local plum-line and magnetic north. Note 
that the IMU orientation does neither refer to the orientation of 
the GPS co-ordinate system nor the co-ordinate system of the 
camera or observer. 
The user of the ARS can choose from two ways of displaying 
the superposition of virtual and real images. One can use a 
portable computer or a retinal display (see figure 2.). The retinal 
display used here is the Microvision = Nomad 
(www.microvision.com). The Nomad is a wearable mobile see- 
through display that operates even in difficult lighting 
conditions e.g. looking against bright skies. 
The framework for holding all the components is a backpack 
rack (see figure 1). A pole for the GPS-antenna, a tripod and an 
aluminium suitcase are mounted on the backpack. The suitcase 
contains all connectors, rechargeable batteries and a portable 
computer. The portable computer is only put away to the 
suitcase if the retinal display is used for displaying. A tripod 
that is mounted on the backpack carries the camera and an IMU 
measuring the orientation of the camera. A second IMU is 
attached to the retinal display. 
3. DATA BASIS 
The availability of data is a key constraint for the tasks of 
disaster management like e.g. communication, planning or 
simulation. This section of the article outlines which data are 
usually available, meaningful and necessary in the case of SAR. 
Generally, three-dimensional data are needed to create the 
virtual scene for the ARS. A first rough classification of the 
data can be established between: (1) data collected before the 
event, (2) data collected after the event and (3) simulated data. 
3.1 Data Collected Before the Event 
To hold relevant data ready for a catastrophic event is a part of 
disaster preparedness. As part of an emergency preparedness 
program, the plan developed before the construction of a 
building, could be stored in a central database. This could be 
mandatory e.g. for larger buildings accessible for the public. 
These plans could contain the main construction elements, the 
age of the building and the used materials. Already a simple 
overlay of the original construction and the destroyed building 
helps to interpret the situation. To collect detailed 3D 
construction information of all buildings of a city is obviously 
an enormous effort. A digital surface model of the city, e.g. 
measured by an airborne laser-scanner, could substitute the 
missing three-dimensional information. 
3.2 Data Collected After the Event 
As proposed by Schweier et al. (2003), airborne laser-scanner 
reconnaissance after the event seems to be suited best to get a 
quick survey of the number of the damaged buildings. The 
910 
visual interpretation of the surface model is also useful. By 
selecting two points of the surface model the user can measure 
distances between objects that cannot be reached by a person. 
This is even more important in the case of collapsed buildings, 
because climbing the debris may be enough to unsettle the 
rubble and cause further loss of cavities. The superposition of 
laser-scanner data and reality using an ARS helps to interpret 
the surface model and to select the correct points. 
  
  
Figure 2. Left: hand-held option. Right: see-through option. 
It should be pointed out that even the ARS itself could be used 
to create three-dimensional information. The creation of 
geometry by the ARS is possible even if no prepared data are 
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