ERCIM News No.25 - April 1996 - CLRC

Computer Graphics Metafiles on the World Wide Web

by Roy Platon

The phenomenal growth of the World Wide Web has in part been due to its use of Graphics within pages. Up till now these have all been image formats eg JPEG, GIF, PNG. It is now generally agreed that a vector or drawing format is needed, as this is better for displaying data such as engineering drawings and graphs. After a short debate it was agreed that the ISO standard Computer Graphics Metafile (CGM) best satisfied the requirements. The Rutherford Appleton Laboratory is now commencing a project to integrate their CGM Viewer (RAL-CGM) more fully into the Web.

"Yet Another Graphics Format" was needed on the World Wide Web as a vector or graphics format offers some advantages over the current image formats: CGM was chosen as it was an established and well used International Standard, many software products could produce CGM files and the files are compact.

The first step in getting CGM accepted as a key web format was to get it registered as an Internet mime type. This was done in December 1995 and the mime type image/cgm may now be used in email or referred to in HTML documents.

The second step was to have an helper application available, which could display the metafile. There are now at least three freely available products which are able to display a CGM for Unix and Windows. These are Gplot from Pittsburgh Supercomputer Center, Figleaf from Carberry Technologies and RAL-CGM from the Rutherford Appleton Laboratory. All these products may be used as external viewers to any of the Web Browsers.

The last step is to fully integrate a viewer with existing browsers, so that CGM may be used as an inline graphics format with the possibility of adding links within the file, rather than using external maps. Inline viewing has the difficulty that different browsers require different interfaces. RAL is working on this and in particular a project is now starting within ERCIM and W3C to integrate RAL-CGM within the Arena browser, and to investigate how to use the added features of CGM within documents.

Please Contact:
Roy Platon - CLRC
Tel: +44 1235 445764

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