Quick Reference

3.4.2 Binary CGM caveats

A Yorick binary CGM conforms to all the recommendations of the ANSI Computer Graphics Metafile standard. Unfortunately, this standard is very outdated. Unlike PostScript, the CGM standard does not specify where the ink has to go on the page, so that every program which interprets a CGM draws a somewhat different picture. Fonts and line types vary a great deal, as does the absolute scale of the picture. The Yorick distribution includes a binary CGM browser, gist (Gist is the name of Yorick's graphics package). The gist browser can convert a binary CGM generated by Yorick into exactly the same PostScript file that Yorick would have produced. No other CGM reader can do the same.

Yorick includes CGM support for historical reasons. Unless you like using the gist browser program, you should write PostScript files directly. If you want to archive lots of pictures, you may be concerned that the PostScript file is much larger than the equivalent CGM. However, standard compression software (such as gzip from project GNU) works much better on the text of a PostScript file than on the binary CGM data, which erases most of the size discrepancy.

If you are serious about archiving pictures, you should strongly consider archiving the raw data plus the Yorick program you used to create the pictures, rather than any graphics hardcopy files. Often this is even more compact than the graphics file, and it has the huge advantage that you can later recover the actual data you plotted, making it easy to plot it differently or overlay data from other sources.