Going Dynamic and External - AutoCAD 2012 - page 408

But blocks don't have to be static creations. Instead of having a half-dozen regular
blocks for a half-dozen different door sizes, you can create a single dynamic block that
includes all those sizes. Unlike a regular block, in which every instance of a particular
block is geometrically identical, each instance of a dynamic block can display geometric
variations. For example, you can insert one furniture block three times and have one in-
stance display as a sofa, one as a loveseat, and one as an armchair. I introduce block au-
thoring — the process for creating and editing dynamic blocks — in this chapter.
There's no question that creating practical, efficient, easily useable dynamic
blocks is a complex process. A simpler way of achieving similar results (and
without the hassle of creating dynamic blocks) is AutoCAD 2012's new associative
array feature. Associative arrays are also dynamic — you can edit them by chan-
ging the number of items or by adjusting various other parameters. Associative
arrays are in no way a substitute for dynamic blocks, but they bridge the gap
between the simple arrays I explain in Chapter 11, and full-blown dynamic blocks
as described in this chapter.
An external reference drawing, or xref, is like an industrial-strength block. An xref is a
pointer to a separate drawing outside the drawing you're working on. When you attach a
reference drawing, it appears on-screen and on plots as part of your drawing, but it con-
tinues to live as a separate document on your hard drive or network. If you edit the ex-
ternally referenced drawing, the appearance of the drawing changes in all drawings that
reference it.
A raster image file stores a graphical image as a series of dots. Raster files are good for
storing photographs, logos, and other images, whereas AutoCAD 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
AutoCAD vector files by attaching them to your drawing files, and the External Referen-
ces palette makes the process straightforward.
Before AutoCAD 2007, external references meant AutoCAD drawing files (and
only AutoCAD drawing files) that you attached to your current drawing. Images
were (and still are) raster graphics files that you attached in a similar way but
with a different command. In AutoCAD 2007 and later, External References is the
name of the palette with which you attach and manage not only externally referen-
ced AutoCAD drawings (xrefs) and 2D MicroStation DGN drawing files, but also im-
age files and DWF or PDF underlays. ( DWF stands for Design Web Format; a DWF is