Computer Graphics Metafile

Usage Standardized platform-independent format used for the interchange of bitmap and vector data. Comments CGM is a very feature-rich format which attempts to support the graphic needs of many general fields (graphic arts, technical illustration, cartography, visualization, electronic publishing, and so on). While the CGM format is rich in features (many graphical primitives and attributes), it is less complex than PostScript, produces much smaller (more compact) files, and allows the interchange of very sophisticated and artistic images. In fact, so many features are available to the software developer that a full implementation of CGM is considered by some to be quite difficult. Nevertheless, CGM use is spreading quickly. CGM (Computer Graphics Metafile) was developed by experts working on committees under the auspices of the International Standards Organization (ISO) and the American Standards National Institute (ANSI). It was specifically designed as a common format for the platform-independent interchange of bitmap and vector data, and for use in conjunction with a variety of input and output devices. Although CGM incorporates extensions designed to support bitmap (called raster in the CGM specification) data storage, files in CGM format are used primarily to store vector information. CGM files typically contain either bitmap or vector data, but rarely both. The newest revision of CGM is the CGM:1992 standard, which defines three upwardly compatible levels of increasing capability and functionality. Version 1 is the original CGM:1987 standard, a collection of simple metafile primitives. Version 2 metafiles may contain Closed Figures (a filled primitive comprised of other primitives). Version 3 is for advanced applications, and its metafiles may contain Beziers, NURBS, parabolic and hyperbolic arcs, and the Tile Array compressed tiled raster primitive. CGM uses three types of syntactical encoding formats. All CGM files contain data encoded using one of these three methods: CGM is intended for the storage of graphics data only. It is sometimes (erroneously) thought to be a data transfer standard for CAD/CAM data, like IGES, or a 3D graphic object model data storage standard. However, CGM is quite suited for the interchange of renderings from CAD/CAM systems, but not for the storage of the engineering model data itself. CGM supports and is used by the Graphical Kernel System (GKS) standard, but is something completely different. GKS, which is in fact an API graphics library specification, is often mistaken for a graphics file format. CGM has found a role on most platforms as a method for the transfer of graphics data between applications. Programs that support CGM include most business graphics and visualization packages and many word processing and CAD applications. Vector primitives supported by Version 1 CGM metafiles include lines, polylines, arcs, circles, rectangles, ellipses, polygons, and text. Each primitive may have one or more attributes, including fill style (hatch pattern), line or edge color, size, type, and orientation. CGM supports bitmaps in the form of cell arrays and tile arrays. The logical raster primitives of CGM are device-independent. A minor point, but one worth noting, is that the three flavors of encoding supported by CGM may not all be readable by all software applications that import CGM files. Despite the existence of a solid body of rules and encoding schemes, CGM files are not universally interchangeable. Many CGM file-writing applications support different subsets of standard features, often leaving some features out that may be required by other CGM readers. Also, because CGM allows vendor-specific extensions, many (such as custom fills) have been added, making full CGM support by an application difficult. The CGM:1987 standard included a "Minimum Recommended Capabilities" list to aid developers in implementing a CGM application capable of reading and writing CGM metafiles correct