From Cheap Tricks, XXX 96 Issue

Published By:
Shu Associates, Inc.
120 Trenton St., Melrose, MA 02176-3714
(617)662-0020 (FAX Same)
eshu@world.std.com

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Those of you with long experience with CAD (and with MS-DOS) know the importance of maintaining "clean" files. Others of you may have heard about the need to "scrunch" your CAD files. Both of these needs relate to a unique phenomenon of MS-DOS computer files sometimes referred to as the one way balloon effect, because the files always get bigger, never smaller.

With CAD files, as well as many other large file formats, data is stored chronologically by input. Because of this fact, the longer you work on the file, the larger it becomes in overall size -- even if you have been doing largely editing work that may have actually reduced the number of entities in your file. Picture that you are working on a long scroll on which your commands are must be listed at the end of the list. Even when deleting items, you don’t simply erase an earlier command, but your must write a delete command down at the bottom of the list. Naturally the longer you work on this scroll, the longer the list becomes.

The way around this problem is to re-compile the file. With some small files, this process is done automatically. In others, you must use the "Save As" com-mand rather than the "Save" command. In DataCAD (as well as other CAD programs) the re-compiling process is done via layering out and layering back in. A CAD file is basically a collection of layers files with an overriding drawing header that defines some of the basic parameters. The longer you work on your CAD file, the longer that scroll becomes until you save out the individual layers, which then re-constitutes the data into its most compact size. When you open a new drawing and load those layers back in, the new CAD file has been "scrunched" or re-compiled into its most efficient size. If you have never done this process before, do it with a drawing that you have worked on for some time and you will be amazed to find that your new CAD file may be hundreds of kilobytes smaller.

Another plus of layering out and then back into a new drawing file is that it keeps your files "clean". By this term, we mean that it rids the file of many potential problems waiting to corrupt your file. Picturing that long scroll, you can imagine that with numerous editing commands, a single entity might have tens of different alterations made to its basic parameters. It’s our gut feeling that this type of situation makes those stupefying internal diagnostic errors much more likely to occur.

DataCAD’s Layer Utility macro will aide you in the process of "scrunching" your drawing file by automating the process for you. Those of you who have watched with keen interest the development of the new REFeree system by ARCHSoft will note that it automatically keeps drawing files "scrunched" because it stores the basic data not by drawing files but by layer files!

So now that you know about this effect, keep your drawings clean and keep ‘em scrunched, and we bet that you will have a lot fewer problems with fatal and internal diagnostic errors.