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
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 picture is scalable so detail can be expanded and inspected
- the metafile can be smaller than an image file
- it is possible to associate links with graphics primitives in the
- primitives are drawn on the screen (not scanned).
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
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.
Roy Platon - CLRC
Tel: +44 1235 445764
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