Читать книгу AutoCAD For Dummies - Ralph Grabowski - Страница 64

As you zoom and pan around the drawing, you may wonder how the image you see onscreen is related to the DWG file that AutoCAD saves on the hard drive. Well, maybe you don’t wonder about it, but I tell you in this section anyway.

When you draw and edit objects, AutoCAD stores all their geometrical properties (that is, location and size) in a highly precise form — technically, double floating-point precision. The program always maintains this precision when you save the DWG file. For reasons of computer performance, however, AutoCAD does not use that high-precision form of the data to display the drawing onscreen. Instead, AutoCAD converts the highly precise numbers in the DWG file into slightly less precise integers in order to create the view you see onscreen.

The happy consequence of this conversion is that zooming, panning, and other display changes happen a lot faster than they would otherwise. The unhappy consequence is that the conversion can make circles and arcs look like polygons. AutoCAD solves this problem by regenerating the drawing (also known as performing a REgen operation).

In most cases, AutoCAD regenerates drawings automatically whenever it needs to. You sometimes see command-line messages such as Regenerating model or Regenerating layout, indicating that AutoCAD is handling the regenerating for you.

If, on the other hand, you see the command-line message Regen queued, AutoCAD is warning you that it’s not performing a regeneration, even though one might be advisable. In addition, you might see the warning message About to regen -- proceed?. AutoCAD is saying, “What the drawing looks like onscreen now may not exactly match the real version of the drawing database that’s stored when you save the drawing. I’ll update the display version at the next regeneration.”

You can control whether regenerations happen automatically by using the REGENMODE system variable. See the online Help system for more information on this variable, and see Chapter 23 for general information on system variables.

The REgenAll command, available only from the command line, regenerates all viewports in a paper space layout. If you run the REgenAll command in model space, it has the same effect as the ordinary REgen command.

If you zoom in a long way in a large drawing that has small circles and arcs and you find them converted into hexagons, simply run the REgen command. You can also minimize this effect in the future by running the VIEWRES command and increasing the value from the default of 1,000 to as high as 20,000 although doing so can also slow down a complex drawing. This value is stored in the current drawing, so you can set up the template file (covered in Chapter 4) to cover most of your work.

Almost every new release of AutoCAD has improved graphics performance. The program has come a long way from the so-called high-resolution 640 x 480 16-color Tecmar Graphics Master adapter, which I started with in the 1980s.