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To implement the universal operations into the VGIS prototype, it was necessary to reorganize and combine 
the necessary analytic and administrative functions (e g. building topology) of the underlying GIS and find the 
best way to connect the VGIS operators directly to each of the underlying GIS. 
For future work, there will still be the problem of combining datasets and operations of different GIS, possibly 
partly depending on the data contents as well as on their precision. That implies a decision on which format to 
use when different datasets and datamodels are involved. Hopefully that phase will fall in a period of a 
uniquely defined OGIS Data Model and OGIS Service Interfaces which will alleviate this problem. 
4 THE VGIS PROTOTYPE 
4.1 Hard-and Software 
VGIS has been developed on a personal computer connected to a workstation via an X server. Limited 
resources made it necessary to rely as much as possible on standard software under the UNIX operating 
system. The initial implementation uses the public domain package GRASS as GIS. A commercial program 
called WiT originally developed for image processing, was used as a tool for processing plan generation. 
Additional functions are implemented in C and C++, while the necessary Motif-based windows were developed 
with the graphical user interface builder X-Designer. Currently the VGIS prototype is extended to Arc/Info as 
a vector based GIS whose abilities to create and design windows will be used to submit parameters to the 
VGIS operations in an interactive mode. 
4.2 Design and Functionality of the Prototype 
VGIS opens with a shell script that first starts an Arc/Info server in the background and calls a C++ program 
which allows the user to define - within a Motif window - the environment variables required to run GRASS. 
Once they are set correctly, a VGIS-adapted WiT session is started. WiT controls the actual functionality of 
VGIS. Only after WiT is terminated, this control is returned to the initial shell script which then removes the 
Arc/Info server and calls again a C++ program that deletes all temporary files and ends VGIS.