19 PROGRAMS THAT BUILD ON AUTOCAD

By David Cohn

For many who use it, AutoCAD is more than just a computer program: It's a way of life. Offices once filled with drafting tables and T squares are now occupied by rows of personal computer design stations. And Autodesk's AutoCAD is the program running on more than 70 percent of those stations.

While not the first CAD package available for the PC, AutoCAD stood out from the beginning, because it offered users the ability to customize many of its features. That prompted many early customers to experiment, first altering the program's menu structure, and later writing scripts and custom macros to speed up repetitive tasks. In 1986, Autodesk added a complete programming language, AutoLlSP, which further enhanced AutoCAD's customization capabilities. With AutoLlSP, users could add new commands to the program to delete all drawing entities of a particular type or automatically save a drawing after a specified interval, for example_thus tailoring the package to fit their individual needs.

In Release 11, Autodesk has gone further, adding a new programming interface, the AutoCAD Development System (ADS), that lets developers write more complex applications in high-level programming languages such as C; the applications can then be loaded and called using AutoLlSP functions. An example is Autodesk's own solids-modeling software, Advanced Modeling Extension (AME), which is available as an option for Release 11.

AutoCAD as Graphics Engine

Beyond its use in such fields as architecture and engineering, you can find AutoCAD in the offices of cartographers, boat builders, technical illustrators, land managers, and medical engineers. The specific drawing needs of these various professions are, of course, quite different; add-ons adapt AutoCAD to facilitate what is needed. For example, parallel lines may represent a wall to an architect; to a cartographer, they may represent a roadway. Once the lines are on paper, the observer can determine their meaning, but while the drawing is being created, the draftsman should not have to think about what those lines mean. Indeed, he should no longer need to draw two individual lines. With the right add-on program, the architect need only draw walls; the cartographer, roads.

Yet these vertical markets represent just a portion of the available offerings. A very different category of add-ons provides important generalized features missing from AutoCAD, as opposed to those aimed at specific disciplines. These horizontaL utilities include such items as text editors, fonts, hatch patterns, links to external databases, and file managers that let you view and manipulate AutoCAD drawing files without having to load AutoCAD. While vertical-market applications appeal only to users within the targeted markets, these general utilities are useful to virtually anyone who uses AutoCAD, and they may even be valuable to those who don't use the program but work closely with others who do.

Horizontal AutoCAD utilities are nearly as numerous as specialized vertical-market applications. PC Magazine counted no fewer than 300 general-purpose utilities among more than 1,000 third-party programs listed in Autodesk's AutoCAD Resource Guide. These included seven packages of fonts or hatch patterns; five plot spoolers; ten programs for editing and managing shapes, fonts, and menus; and ten graphics display drivers that vastly increase the speed of VGA graphics boards when used with AutoCAD (see the sidebar "Display-List Drivers: Moving Around AutoCAD in Real Time"). The guide also includes examples of two especially popular kinds of AutoCAD utilities: the ten file-viewer/drawing-management programs and the nine text editors reviewed on the following pages. Because these products differ so greatly in their intended purpose, we chose not to award an Editors' Choice in either category.

Visual file Management

The casual glance over the drafter's shoulder was replaced by a puzzled stare at a CRT. It is difficult to view an entire 24-by-36-inch drawing within the confines of a monitor. And if you've forgotten the exact filename of the drawing you are looking for, you may need to load drawing after drawing, typing each filename at AutoCAD's main menu until you find the right one.

A number of developers rose to the occasion, creating programs that let you display AutoCAD drawing files much more quickly by simply highlighting filenames, without the need to load AutoCAD first. This was no easy feat. Autodesk has never published specifications for its .DWG file format, and in fact, the company has changed that format with each release of the program as new features were added. Thus, developers have had to reverse-engineer their viewing utilities-and keep up with constant change.

Getting Around

Instead of an entire drawing, though, you may often need to locate a single block-a collection of entities saved as a unit-that you would reuse if only you could find it. Most drawing viewers, therefore, give you the ability to display individual blocks within a drawing and to turn individual layers on and off.

As competition among these programs has heated up, developers have added other features. For example, most let you copy, rename, or delete files simply by clicking on their filenames with a mouse. Others can quickly produce a print or plot of any drawing. Still other programs let you dispense with the need for check prints entirely by adding nondestructive "redline" notes that the draftsman will see the next time the drawing is loaded.

Total Drawing Management

Not all drawing viewers are created equal, however. Indeed, some developers have deciphered the .DWG file format more adequately than others, and Autodesk continues to complicate their jobs. AutoCAD, Release 11-the latest version of the program-adds several new features that confound many of the viewing programs. The most troublesome, called paper space, enables AutoCAD to display multiple views of a drawing on-screen at once, exactly as it will later be plotted. Another, reference files, lets you include several external files in a master drawing without actually loading the referenced drawings' entities; this is similar to dynamic data exchange (DDE) under Windows.

Add to this mix the desirability of being able to display formats besides .DWG, plus the need for each developer to invent its own graphical user interface (one viewer runs under Windows, and none look much like AutoCAD), and you have a very broad feature set. Yet if you use AutoCAD or work with AutoCAD-related files, you do need a drawing viewer--and one of these ten programs will probably meet your needs, though none of them are right for everybody.

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