Expert Training

Overview

In This Chapter

• Introducing blocks, external references (xrefs), and raster images

• Creating block definitions

• Inserting blocks

• Using attributes in blocks

• Attaching and managing xrefs

• Controlling xref paths

• Attaching and managing raster image files

Chapter 6 shows you how to copy objects within a drawing or even to another drawing. That’s one way to use CAD to improve drafting efficiency. You can copy a DWG file and then modify it to create a similar drawing — an even better productivity-booster, as long as you’re in the habit of making similar drawings. But all of those are baby steps compared to the techniques that I cover in this chapter: treating drawings, parts of drawings, and raster images as reusable and updateable modules. If you want to make drafting production more efficient with CAD, then you want to know how to use blocks, xrefs, and raster files.

A block is a collection of objects grouped together to form a single object. You can insert this collection more than once in the same drawing, and when you do, all instances of the block remain identical, even after you change the bock definition. Although a block lives within a specific drawing, you can transfer copies of it into other drawings. You can add fill-in-the-blank text fields called attributes to blocks.

An external reference, or xref, is like an industrial-strength block. An external reference is a pointer to a separate drawing outside the drawing you’re working on. The referenced drawing appears on-screen and on plots as part of your drawing, but it continues to live as a separate document on your hard disk. If you edit the externally referenced drawing, the appearance of the drawing changes in all drawings that reference it.

A raster file (also called a bitmap file) stores a graphical image as a series of dots. Raster files are good for storing photographs, logos, and other images, whereas CAD vector files are good for storing geometrical objects such as lines and arcs, along with text and other annotations for describing the geometry. Sometimes it’s handy to combine raster images with CAD vector files, and AutoCAD’s IMage command makes the process straightforward.

Blocks, external references, and raster images enable you to reuse your work and the work of others, giving you the potential to save tremendous amounts of time — or to cause tremendous problems if you change a file on which other peoples’ drawings depend. Use these features when you can to save time, but do so in an organized and careful way so as to avoid problems.

Tip The way in which you use blocks and especially xrefs will depend a lot on the profession and office in which you work. Some disciplines and companies use these drawing organization features heavily and in a highly organized way, while others don’t. Ask your colleagues what the local customs are and follow them.