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CGM is an
ANSI/ISO 8632 standard format since 1987 for representing
2-D technical illustrations. Developed by experts working
under the auspices of ISO and ANSI, and was designed
specifically as a common format for the platform-independent
interchange and storage of raster (bitmap), vector and
text data. CGM files typically contain vector, raster and
text data.
CGM offers the advantage of small file size and resolution
independence, while not being tied to a specific software
package or hardware platform. CGM was adapted by the US
Department of Defense as one of the
CALS initiative standards.
CGM is defined in ISO
8632:1992 together with Amendments 1 and 2, and specifies a
two-dimensional data interchange standard which allows graphical
data to be stored and exchanged among graphics devices,
applications, and computer systems in a device-independent
manner.
CGM format has a structure that can represent vector graphics
(e.g., polylines, ellipses, NURBS), raster graphics, and text.
Although initially a vector graphics format, it has been
extended in three upwardly compatible extensions to include
raster capabilities and provides a very useful format for
combined raster and vector images.
A metafile is a collection of elements. These elements may be
the geometric components of the picture, such as polyline or
polygon. They may be details of the appearance of these
components, such as line colour. They may be information to the
interpreter about how to interpret a particular metafile or a
particular picture. The CGM standard specifies which elements
are allowed to occur in which positions in a metafile
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