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• robust measurement system with stable image geometry (interior orientation has to be 
done only once, there is no time-depending deformation), 
• great automation, on-line, and real-time potential, 
• use of digital and A/D converted imagery, 
• capability of image processing for improved presentation, 
• multi-image matching option, 
• high instrument versatility (all photogrammetric and related tools in one system). 
Further decreasing costs and improving performance of hardware will result in more accurate 
and reliable, cheaper and faster processing. Consequently, researchers (GRUEN 1988, 
LOHMANN 1989, DOWMAN 1990) and companies (COGAN & HUNTER 1989, EUGET & VIGNERON 
1988, HELAVA 1989, FAUST 1989) throughout the photogrammetric world are convinced of the 
necessity of proceeding to digital photogrammetry and at several places were encouraged to 
design and develop digital systems. 
ACTIVITIES OF THE WORKING GROUP AT THE TUB 
At the ISPRS meetings 1986 in Baltimore and 1988 in Kyoto the authors reported on their ex 
perimental Digital Stereophotogrammetric System (DSS) based on standard image processing 
hardware. The DSS is capable of automatic or interactive processing of images of different sour 
ces, e.g. Scanning Electron Microscope (KOENIG et al. 1986, 1987) and CCD camera images, 
airborne and satellite scanner (ALBERTZ et al. 1990) data as well as digitized metric camera ima 
gery (KOENIG et al. 1988). 
Experiences made by using the system proved that for Digital Elevation Model (DEM) genera 
tion a combination of the Vertical-Line-Locus method with least squares matching in a stereo 
model, adding several checks for reliability, leads to satisfactory results. The accuracy can com 
pete with that of an analytical plotter. But on a VAX 11/750 the stereoscopic measurement al 
ready takes about 1-2 seconds per point and multiple image matching algorithms will even slow 
down processing speed which means that system performance is just too poor. 
Consequently, from early 1990 onward the TUB working group is engaged in the development 
of a new photogrammetric workstation, the Advanced Digital Stereophotogrammetric System 
(ADSS) based on state-of-the-art technology. 
Design of an advanced System 
A digital photogrammetric station has to fulfill several specifications and hardware requirements: 
• Handling and processing of large stereoscopic images (e.g. 600 MB for a pair of digiti 
zed colour aerial photographs at 25 pm resolution) in reasonable time, 
• three-dimensional evaluation of digital imagery of any kind, 
• automatic evaluation of DEM and digital orthophotos at acceptable processing time 
with sub-pixel accuracy,