The use of FTAM to access graphical pictures across WANs

The demonstration is of the use of file ACCESS in FTAM (as opposed to simple file TRANSFER) to access graphical information. It uses a newly-developed FTAM Document Type which allows remote access to individual graphical pictures stored within a complete sequence of pictures in the ISO standard Computer Graphics Metafile (CGM -- ISO 8632). This allows a remote application to retrieve the exact information it requires, thus minimising the amount of data that is transferred over the network. The demonstration shows that this means that useful distribution of graphics over even a low-bandwidth network (such as between European national X.25 PDNs) is possible.

The demonstration takes the form of an application which provides up-to-date road-traffic information in a graphical form. The user of the application is shown a European road map, upon which he or she can plot a route between a number of cities. The application then uses FTAM to consult a number of sites, each of which stores and maintains a set of "traffic difficulties" pertaining to its local geographical environment. These difficulties are stored at each site in graphical form ie as individual pictures in one or more CGMs Each picture represents the current traffic difficulties pertaining to a small part of the area for which the site is responsible. The application selects only those pictures that are relevant to the user's planned route, retrieves these, and displays them graphically as an overlay on the road map, along the route chosen. The user can then zoom and pan over the route to inspect the difficulties, or if necessary can consult further to try to find a more trouble-free route.

The new FTAM Document Type which allows structured access to the CGM has been developed by the Esprit II project ARGOSI. This has as its aims:

• an advancement of the state of the art in the transfer of graphical information across international networks;
• an improvement to the quality and applicability of standards in this area.

The Document Type has been submitted for international standardisation through EWOS. The project also modified three implementations of FTAM to handle the new Document Type: commercial implementations from Marben and Tecsiel, and the ISODE public-domain implementation. In the latter case the modification also included the addition of two-level hierarchical access with FTAM. This feature was lacking in the standard release of ISODE FTAM, which can support the transfer only of complete files. It is intended that the resulting code will be put into the public domain.