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⟶ CISD and DCI ⟶ Literature ⟶ W3C UK News (1998-2006)
⟶ CISD and DCI ⟶ Literature ⟶ W3C UK News (1998-2006)
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1998
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Issue 14: February 1999

CGM Web Profile

On 21st January, 1999, the WebCGM Profile was released as a W3C Recommendation. Now, for the first time, it is possible to generate drawings like the one below, rather than images, in a standard way on the Web.

CGM

CGM
Full image ⇗
© UKRI Science and Technology Facilities Council

The drawing above takes 15 kbytes to represent it at any level of detail as a CGM, while a 72dpi GIF image would take 32 kbytes.

The Computer Graphics Metafile (CGM) is an ISO standard of long standing (ISO 8632 originally published in 1987) for storing and transferring 2D vector graphics drawings. It is widely used in commercial engineering applications.

CGM has been available on the Web as a plug-in for some time. However, plug-ins from different companies included different subsets of the standard and introduced different ways of handling hyperlinks (often used to move from an overview schematic diagram to a more detailed view).

As CGM is quite a rich standard defining a range of primitives, attributes and grouping facilities, ISO recognises the need for subsets appropriate to specific industry sectors. These are called profiles and there is a standard format for representing these.

W3C has been working with the CGM Open Consortium to define a CGM Profile appropriate for the Web. Members of the CGM Open Consortium who are also members of W3C include companies like Boeing, Inso, Xerox and CCLRC. For detailed information concerning WebCGM, a visit to the CGM Open Web site is recommended:

http://www.cgmopen.org/

Some of the reasons why a vector graphics format is preferable to a GIF image are:

Zoomed in

Zoomed in
Full image ⇗
© UKRI Science and Technology Facilities Council

One of the widely used existing CGM Profiles is that of the Air Transport Association (ATA). This was used as the basis for defining the restrictions to be placed on the Web Profile. To a large extent the subset of graphical facilities defined in the ATA Profile correspond to those in the Web Profile. One major change is that it is possible to define the background as transparent or translucent so that the CGM can be placed on an existing image (for example contours added to a GIF image).

The graphics primitives include symbols, polylines, Bezier curves, areas, rectangles, circles, ellipses, arcs, text, and raster images (PNG and JPEG).

A large part of the work has been in defining the organisation of hyperlinks. It is possible to group a set of graphical primitives in CGM and associate a name with them. Web CGM has defined four group types:

The extent of grobjects, paras and subparas can be specified as the hotlink area or be the target of a link. Viewers are then expected to make sure the complete group is displayed, possibly scaling it to fit into the area available.

Hyperlinking in the CGM Web profile allows a CGM drawing to link to another Web page in the usual way or to another CGM drawing. Multiple links are allowed in which case the browser gives the user the choice of where to go.

When a link points to another CGM picture, there are a number of possibilities as to how the browser should react. Some examples are:

  1. Load the new picture in a new window.
  2. Load the picture into the current frame.
  3. Load the picture over the parent of the current frame.
  4. Replace the current picture by the new one in exactly the same area.

The WebCGM Profile is specified at: http://www.w3.org/TR/REC-WebCGM/

New Members

The number of new Members in January was quite small compared with the rush of the previous month. The total number of members is 317 with a breakdown:

Full Affiliate
Americas 44 145
Europe 28 60
Asia-Oceania 17 23

The new Members since December are:

XML: SGML UK User Group Meeting

On Wednesday, 24th February 1999, RivCom is running an Introduction to XML course under the auspices of the SGML UK Users Group. This course is designed to provide a broad introduction to XML from both a technical and a business perspective.

This full-day event costs only £35.00 for SGML UK members, and £75.00 for non-members, including lunch and refreshments. Admission will be by advance registration only. Tutorial presenters include: Tony Stewart, Director of Consulting, RivCom and Adrian Rivers, Sales Director, RivCom.

On Thursday, 25th February, RivCom will also be contributing to a SGML UK session on SGML, XML and Electronic Commerce.

For additional information (including a detailed course overview) and registration for both events go to: http://www.sgml.org.uk/meetings.htm or http://www.sgml.org.uk/meetings.htm#xmlintro.

The W3C-LA Project Completing

The Esprit Leveraging Action, W3C-LA, that brings you this Newsletter is completing. The official closure was to have been 4th February 1999 but there has been an extension until April to finish off some of the technical work.

The plan is to continue producing the Newsletter monthly as part of the European Offices activities. Each issue will no longer be distributed on paper but will be made available via the local Offices' Web sites. In the UK, we plan to e-mail existing recipients of the Newsletter a notification when each issue is available on the Web. If you would like to take advantage of this service, we would appreciate you filling in the enclosed form or emailing us at: w3c-ral@inf.rl.ac.uk.

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