WebCGM and SVG: A Comparison

Addressing the Need

• CGM Open

• SVG Working Group of W3C

The Requirements

• Scalable

• Efficient

• Revisable

• Object-addressable

• Integratable w/ other Web content

WebCGM

• Cooperation of CGM Open and W3C (World Wide Web Consortium)

• Technical work was conducted by CGM specialists

• Based on ATA profile GREXCHANGE 2.4

• Changes and extensions for web usage

• Additional definition of meta data

WebCGM Overview

• Rich format for raster and vector elements

• Fully developed and structured format

• Compact binary encoding for complex technical graphics

• Increasing support by software developers and end users

• Supported by CGM Open

• Conformance and test procedures

Status of WebCGM

• W3C recommendation since January 1999

• First interoperability demo at the XML show in Granada in April 1999

• First products have been released

SVG

• Scalable Vector Graphics

• Work group of W3C

SVG Overview

• XML tagset, stylable (by style sheets), integrated in and dependent on various other XML standards

• Creative graphics and design

• Integrated, dynamic and animated web sites

• SVG Test Suite available

Status SVG

• Candidate Recommendation

• Final version in January 2001

• Support by various software vendors already announced

• First products released

WebCGM and SVG - Common Geometry

• Lines, polylines, polygons

• Rectangles, circles, ellipses, arcs

• Graphical text

• Closed figures and compound lines

• Polysymbols/Markers

• Smooth curves -- Piece-wise Bezier

• Raster images -- PNG, jpeg

• Clipping

WebCGM and SVG: Simple geometry

SVG:

	<svg width="400" height="400">
	  <g style="fill:none; stroke:green">
	    <line x1="100" y1="300" x2="300" y2="100" 
	          style="stroke-width:5" />
	  </g> 
	</svg>

CGM (text encoded):

	BEGMF 'sample.cgm                       ';
	...
	 BEGPIC 'Picture 1';
	VDCEXT 0,400 400,0;
	 ...
	 BEGPICBODY;
	 ...
	  LINECOLR 5;LINEWIDTH 0.5;LINETYPE 1;
	  LINE 100,300 300,100;
	 ENDPIC;
	ENDMF;

WebCGM and SVG: Text

• All text is Unicode

• graphical text

• non-graphical text, e.g. screentips

• font descriptors

  • CGM: basic 13 PostScript fonts

  • other fonts with font properties allowed

  • SVG: no predefined font, can define own fonts

WebCGM and SVG: Hyperlinking

• Simple hyperlinks

BEGAPS 'myID1' 'grobject' STLIST;
 APSATTR 'name' "14 1 'myObj1'";
 APSATTR 'linkuri' "14 3 'sample.cgm#id(myObj)' 'Click to display obj1' ''";
BEGAPSBODY;
 POLYGON 30,50 70,50 70,15 30,15 30,50;
ENDAPS;
<g>
 <desc>'Click to display obj1'</desc>
 <a id='s12-1myObj1' xlink:href='sample.svg#xpointer(id(myObj))'>
  <polygon points='30,50 70,50 70,15 30,15 30,50'/>
 </a>
</g>

• Link to view context

WebCGM and SVG: Other Links

• Link to symbols

• Link to gradients, filters, fonts, animation in SVG

WebCGM & SVG compared

• WebCGM:

  • Profile of an established ISO standard

  • Communication and exchange in existing customer networks

  • Binary encoding, completely defined, "self contained"

  • No proprietary data

• SVG:

  • Complete new concept, from "scratch"

  • Creative graphics and design

  • Integrated, dynamic, animated web pages

  • xml-coded, stylable, dependent on other files,

    e.g. style sheets

  • Inclusion of any proprietary extensions possible in a different namespace

Comparison: WebCGM & SVG

• Overlap in functionality

  • WebCGM => SVG, conversion without losses

  • SVG => WebCGM, potentially very lossy

Do SVG and WebCGM compete?

No.

Why not?

• SVG is suitable for high quality, creative graphics

  • color requirements

  • text / font requirements

  • animation

  • filter effects

• WebCGM is suitable for technical graphics with long life cycle

  • complexity / size requirements

  • re-authoring capabilities

  • interoperability requirements (lots of data exchange)

  • Compliance with industry standards (ATA, CALS)

So what?

• For a lot of files, SVG will be the better solution.

• For a lot of files, WebCGM will be the better solution

• Expectations:

  • Both formats will coexist and complement each other

Things to watch out for

• Before you convert all of your files to SVG and/or WebCGM:

  • wait for final implementations

  • watch out for restrictions when using files in current web browsers

Design and Development by deepX Ltd.