2 Map or navigation tool. Queries for image coverage usually 
require the definition of a point (POI) or a region of interest 
(ROI) A map-like representation of the area covered by a 
dataset, can ease this task considerably. With the possibility to 
move around and zoom in and out this map regions or points 
can be defined by point and click operations. To visualize the 
content of a database or the results of a query, one may also 
overlay the geographical information with outlines and 
information about any feature with a position or some spatial 
extent. This can be data like images, data gaps, topographical 
features and names, orbit data and many others. 
3 Preview of data. To offer the user the possibility of 
inspecting the data before actually placing an order, one may 
have quicklooks or reduced versions of images available for 
downloading. This feature can also save network bandwidth 
since it avoids the download of unneeded data. Also for 
copyright reasons it is often not possible to provide full 
resolution images before payment is guaranteed. 
4 Ordering data is the most important action which data 
providers want users to do. Therefore it is always easy to use 
this function, whereas distribution of data in most cases is done 
the slow and traditional way by mailing a tape or CD-ROM. 
2 EXISTING SYSTEMS 
2.1 Stand alone software 
As a marketing instrument and for user service data providers 
have developed interface software to their archives and 
catalogues. Early examples for this software were terminal 
based with a commandline or menu interface. Some of these 
products are still in use, even though newer versions with 
graphical user interfaces or WWW-based counterparts are 
available today. An example for this live cycle is the ISIS tool 
from DLR. The graphical version of this tool is GISIS 
(Graphical Intelligent Satellite Information System, Lotz-Iwen, 
1995). It features all four components of such a system as well 
as some additional highlights, like a thesaurus for geographical 
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names. The navigation tool, which is based on a software 
product form Xerox, provides a zoomable vector based map at 
different levels of detail. GISIS is also a multi-catalogue system 
and offers interfaces to different data sets and directories. Even 
though this is one of today's most advanced systems, the 
number of accesses has been almost stable over the past 15 
months. 
This example shows, that a user often avoids to install and 
maintain dedicated software products for different data 
catalogues, especially if one does not plan to use them 
frequently. Compared to the previously described access 
numbers of the IDN interface at GCMD, this clearly indicates, 
that for the user acceptance of a catalogue, the ease of access 
can be more important than the number of available functions. 
Some other examples for special purpose systems are VISTA 
(Visual Interface for Space and Terrestrial Analysis, Snyder, 
1994) and the Arno project (Nativi, 1995). VISTA is very 
special, since it supports a 3D vector representation of data like 
spacecraft ephemeris, sensor positions and the surface of the 
Earth. 
2.2. WWW -based catalogue systems 
Because of the reasons described above WWW-based image 
information systems are playing an important role today. The 
basic idea of the WWW was to present hypertext information 
containing text and images stored in HTML files to user. Build 
in hyperlinks allow easy navigation to other HTML documents 
and access to other Internet tools like ftp and e-mail. This very 
restricted set of functions is designed to present information to 
a rather passive user. To implement interaction with the user all 
user inputs have to be transmitted to the location of the WWW 
server, where a new HTML file has to be generated according 
to the user inputs and transmitted back to the user’s site. 
The example of drawing a mark at the location of a mouse click 
over an image displayed in an HTML document, shows the 
resulting intensive network traffic. First the coordinates of the 
mouse click have to be transmitted to the WWW server. The 
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Fig. la: A few lines from the dump of a database table containing image names and positions. It is somehow easy to see that the 
images are forming a row. Its much harder to see the overlap between successive images. 
  
  
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Fig. 1b: Enlarged portion of a screenshot showing the positions of the images listed in Fig. 1a. The small overlaps are clearly visible. 
198 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1.-Vienna 1996 
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