
Date: Wed, 1 Nov 1995 00:13:14 +0000
From: Alan Francis <A.H.Francis@open.ac.uk>
Subject: Final version of CGM Media Type registration

To CGM MIME registration people

Here is the final version of the Media type registration proposal for CGM.
Note that version and profile are now required parameters.
Some minor changes have been made as a result of comments on the almost final version.

Alan Francis
31.10.95

      =============================================================      
      To:  IANA@isi.edu
      Subject:  Registration of new Media Type content-type/subtype

      Media Type name: image

      Media subtype name: cgm

      Required parameters: version=n
		        ProfileId=profilename

      Optional parameters: None

      Encoding considerations: Recommend Base64 MIME encoding  where transport 
      not 8 bit clean

      Security considerations: None

      Published specification: ISO 8632:1992, IS 8632:1992 Amendment 1 (1994) 
      and IS 8632:1992 Amendment 2 (1995)

      Person & email address to contact for further information: Alan Francis
      Email: A.H.Francis@open.ac.uk


      Background

      CGM, Computer Graphics Metafile, is the International Standard for the 
      storage and transfer of 2D picture description information. It is
      specified in IS 8632:1992 Parts 1-4. It can handle vector graphics and
      images. It stores pictures in a way which is independent of any
      particular software, computer or graphics device. 

      CGM offers the Internet community the first option for a vector-based 
      (i.e., line-art) image type.  Currently, the valid image types are JPEG, 
      and GIF, both raster or bitmap type image files.  Vector images allow for 
      greater detail and clarity at multiple zoom levels. Also, they are usually 
      much more compact than the equivalent bitmap.

      CGM is used by a number of other standards including the Office Document 
      Architecture (ODA) standard, ATA within the commercial aviation industry, 
      J2008 within the automotive industry and the CALS (Computer-aided 
      Acquisition and Logistics Support) specification of the US Dept of Defence. 
      The CGM can be used to exchange pictures between different types of 
      applications. CAE/CAD, graphic arts, business graphics and desk top 
      publishing packages can all use the CGM to exchange graphical information. 

      More than 300 applications can generate and/or interpret CGM files.
      There are a number of public domain CGM generators and interpreters 
      available.

      Parameters and Encoding

      The CGMs should use the binary encoding, as specified in 
      IS 8632:1992 Part 3.  

      Valid version numbers are those specified in ISO 8632:1992 and any 
      amendments. (Currently Versions 1, 2 and 3 are specified in ISO 8632:1992 
      and version 4 is specified in IS 8632:1992 Amendment 2 (1995) which adds 
      Application Structures which can be used to support hyper-links.)
      The versions are upward compatible in the sense that a valid Version 1
      metafile is a valid Version 2 metafile, Version 2 is a subset of Version
      3, and Version 3 is a subset of Version 4.
     
      The version number in this parameter must be the same as the version 
      number within the CGM file itself.  It is recommended that only Version 1 
      CGMs be used initially because most current software handles 
      Version 1 CGMs. It is expected that in the next year or two software 
      will be upgraded to handle version 3 and 4 CGMs.  Version 2 is not 
      expected to be widely used as a target implementation level.

      Profiles are used to specify limits, for example the maximum number
      of points in a polygon or the set of fonts which can be used. 
      Reliable CGM interchange can only be assured with CGMs conforming 
      to one of the principal profiles. The profile declared in this parameter
      must be the same as the profile declared within the CGM itself.

      Valid profiles are those registered with ISO as International 
      Standardized Profiles (ISP). The Model Profile, as specified in 
      IS 8632:1992 Amendment 1, and three others are being registered 
      as ISPs (DISP 12071-1 Basic Scientific and Technical, DISP 12071-2 
      Advanced Scientific and Technical, DISP 12071-3 Basic Presentation 
      and Visualisation (Model Profile), DISP 12071-4 Advanced 
      Presentation and Visualisation). 


      Acknowledgements

      The following people have contributed towards this registration proposal:
      Alan Francis (Page Description, UK)
      Brian DiAntonio (Electronic Book Technologies/Carberry, US) 
      Dr Anne Mumford (Advisory Group on Computer Graphics, UK)
      Lofton Henderson (Henderson Software Inc, US)
      Steve Carson (GSC Associates, US)


      Contact: Alan Francis
      Email: A.H.Francis@open.ac.uk
      Phone: +44 1908 316921
      Address: Page Description, 6 Spencer St, New Bradwell, Milton Keynes,
               MK13 0DW, UK.


