|
|
| A |
The
Computer Graphics Metafile (CGM) is the
international standard for storage and exchange of two-dimensional
graphical data. Initially developed as a vector format it has been
extended to include raster capabilities and provides a useful format
for combined raster and vector images.
|
| Q |
What
does "metafile" mean? |
| A |
A
metafile is a list of commands that can be
executed to draw geometric components, such as polylines, polygons or
text elements. The metafile may also include commands to control the
style of these objects such as line color. The CGM standard specifies
which elements are allowed to occur in which positions in a metafile.
|
| Q |
What
is the difference between a Vector and
a Raster image? |
| A |
A
vector graphic
is a graphic drawn using mathematically defined objects such as
polygons, lines and text. A Raster graphic is drawn using an array of
dots.
|
| Q |
Is
CGM a Raster or a Vector format? |
| A |
CGM
is a robust Vector graphics format that
can also be used to describe Raster images. A more accurate description
would be to say it is a geometric description language. CGM describes
pictures and graphical elements in high level geometric terms such as
lines, circles, arcs, ellipses, polygons, text strings, and cell
arrays.
|
| Q |
What
sort of standard is CGM? |
| A |
CGM
provides a file format suitable for the
storage and retrieval of image information. The file format consists of
an ordered set of elements that may be used to describe images in a
neutral way that can be understood by different systems, applications
and devices irrespective of architecture.
CGM
became an international standard
in 1987 as ISO/IEC 8632 and was adopted as a national standard in many
countries. Following a number of published amendments to give it
increased functionality a revised standard was published in 1992 as ISO
8632:1992 and again in 1999 as ISO 8632:1999
|
| Q |
Why
are there different versions of CGM? |
| A |
Different
CGM files can conform to different
versions of the Standard as it was being developed. There are three
main versions of CGM in common usage.
Version 1 refers to CGM
files that conform to the original, 1987, version of the published
standard.
Version 3 refers to CGM
files that conform to the 1992 version of the standard which includes
advanced graphical elements such as splines and polybezier curves. It
also enriched the graphical attributes to allow for greater definition
of engineering drawings and technical illustrations. Version 3 is
mainly used in Technical Illustration systems.
Version 4 refers to CGM
files that conform to the 1999 version of the standard that added
Application Structuring. This allows the CGM to contain non-graphical
information in addition to graphical content. This allows CGM to be
used for a wide range of application interactive graphics, hotspots and
hyperlinking.
|
| A |
Profiles
are a subset of the standard
developed independently by standards groups within specific industries.
The purpose of a profile is to improve the interoperability of CGM
within a specific technical community. The most popular profiles are
those developed by the aerospace, defense, petroleum, automotive, and
rail industries. The World Wide Web Consortium (W3C) has also
developed a specific profile for the use of CGM on the Web.
|
| A |
Web
CGM is a profile of the CGM standard
(ISO 8632:1999) that describes how CGM vector, raster, and hybrid
graphics are to be used on the web. It was developed between the W3C
and the CGM Open Consortium and represents a consensus of users and
vendors of CGM on a way to exchange dynamic hyperlinked CGM files over
the Web.
WebCGM provides a vendor-neutral standard for 2D graphics that enables
creators and consumers to exchange, view, and browse intelligent,
vector, raster, or hybrid graphics reliably. Users are able to create
graphics in one tool and view / browse them in another without loss or
distortion of information.
|
| Q |
What
are the Industry Specific CGM Profiles? |
| A |
The main industry defined CGM
profiles are
as follows:
CALS CGM profile is a
Department of Defense standard (MIL_PRF-28003 Rev B) entitled "Digital
Representation for Communication of Illustration Data: CGM Application
Profile." It is part of the CALS (Continuous Acquisition and Life-Cycle
Support) family of standards.
ATA CGM profile is part of
the Air Transport Association (ATA) specification 2100 that governs
technical documentation for the manufacture and operation of commercial
airplanes. The exchange profile GREXCHANGE is based on CGM Version 3
and is suitable for the exchange of technical manuals, publishing
applications, and visualization. A second profile IGEXCHANGE provides
for the transfer of intelligence associated with graphical data and is
based on application structuring as defined in CGM Version 4.
CGM PIP is the Petroleum
Industry Profile for CGM. It was developed for graphical interchange
between applications in the petroleum exploration and production
community. This standard is based on CGM Version 3 and CGM+, a format
for graphical representation of geophysical data.
J2008 is the automotive
industry standard for the exchange of technical documentation and
states that all graphics should be in CGM format. It references the ATA
2100 CGM profiles.
RIF / EPECS is the
Electronic Parts Catalog Exchange Standard of the Rail Industry Forum.
It also references the ATA 2100 specification for the use of CGM as
graphics exchange standard.
|
|
|
|
