LT On-line: Lesson 121 Mar, 2001 By: Mark Middlebrook
Why Line when you can Pline?
1: A polyline primer
After all of the conceptual
"heavy lifting" in my previous sets of LT Online lessons on
blocks and xrefs, we'll take a breather this month and consider when and
how to use the Pline command. If you're one of those LT or AutoCAD users
who doesn't fully appreciate why Pline is better than the Line command
for many drawing tasks, then use this lesson to develop your polyline
The procedures described
here work with AutoCAD LT 98-2000i and AutoCAD Release 14-2000i.
By now, you're familiar with using the Line command to draw straight line
segments-either a single segment or a series of segments that lie end
to end. The Line command is fine for some drawing tasks, but the Pline
(or Polyline) command is a better, more flexible choice in many situations.
The most important differences between these two commands are:
The Pline command draws curved segments as well as straight ones (figure
1). Curved polyline segments are circular arcs, of the sort that you
can draw with the Arc command.
The Line command draws a series of single line segment objects. Even though they appear to be linked onscreen, each segment is a separate object. The Pline command, on the other hand, draws a single, connected, multi-segment object. Figure
The last difference is the most important. When you use the Line command, AutoCAD draws a type of object called, appropriately enough, a line. AutoCAD stores each segment as a separate line object. The Pline command draws a special kind of multi-segment object called a polyline (sometimes referred to as a pline because of the command name). AutoCAD stores all of the segments together as one object.
Why is this difference important? With the Pline command, you can group together segments that belong together. If you draw a series of end-to-end segments, there's a good chance that those segments are logically connected. For example, they might represent the outline of a single object or a continuous pathway. If the segments are connected logically, then it makes sense to keep them connected in AutoCAD.
The most obvious practical
benefit of grouping segments together into a polyline is that many editing
operations are more efficient when you use polylines. If you move one
line segment, other segments that you drew at the same time don't move
with it. The same is true for other common editing operations, such as
copying, erasing, rotating, and mirroring. When you select any segment
in a polyline for editing, the entire polyline is affected.
In short, you can
get the same plotted results by using the Line and Arc commands or the
Pline command, but Pline results in objects that are more logically organized
and that respond more sensibly to editing operations.
Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!