What use are Polylines?
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URL: https://www.cadforum.cz/forum_en/forum_posts.asp?TID=9438
Printed Date: 19.May.2026 at 14:51
Topic: What use are Polylines?
Posted By: rickduley
Subject: What use are Polylines?
Date Posted: 31.Jul.2013 at 01:25
Heretical question? My technical drawing background is drafting board and pencil based. In that work environment polylines do not exist. The simple fact is that I haven't figured out what I would use them for.  It is a mystery to me why AutoCAD provides a button for polylines on the toolbar but does not for splines. Splines are useful! Splines are handy! Yet to get to splines you have to go burrowing down the menus! What is so important about polylines?  ------------- Outside of a dog a book is a man's best friend. Inside of a dog it's too dark to read! Graucho Marx |
Replies:
Posted By: John Connor
Date Posted: 31.Jul.2013 at 11:47
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A simple example. A four sided box drawn with the line command consists of four separate entities. A four sided box drawn with a continuous polyline is a single entity. If you have to move, copy, or rotate the box it would be simpler if it were drawn with a polyline. Polylines can also be given a "width" which is something that cannot be done with a line. While splines may be useful to use many people can go their entire lives without ever having need to use them. ------------- "Humans have a strength that cannot be measured. This is John Connor. If you are reading this, you are the resistance." <<AutoCAD 2015>> |
Posted By: rickduley
Date Posted: 01.Aug.2013 at 04:21
I guess the same can be said about Polylines. One day there will be some problem and I'll say to myself, "Here is a job for Polylines!" Then I'll know what they are for!  ------------- Outside of a dog a book is a man's best friend. Inside of a dog it's too dark to read! Graucho Marx |
John Connor wrote:Posted By: heinsite
Date Posted: 01.Aug.2013 at 08:29
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What use are polylines? Do you ever hatch irregular shapes? How do you do it? Do you select an empty area somewhere in the middle? Will that always work if it contains additional geometry? Do you select all of the individual line segments? That must take a lot of time. Think polyline. Hatch. Select object. Done. It doesn't all have to be on the screen. Do you ever need to determine the area of something? How do you do it? Polyline again. Just select it and look at Properties. Do you ever want to draw an object with real width? How do you do it? Two lines maybe separated by the width? Then filled in? Too much work. Polyline again. The list goes on. Personally (in 2014 at least) I like the ability of adding or removing vertexes. You can't do that with a simple line object. Dave ------------- Dave Hein, P.E. Hawaii District Engineer Kona International Airport AutoCAD Certified Professional Autodesk Expert Elite |
Posted By: jaredlloyd
Date Posted: 01.Aug.2013 at 20:32
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Depending on what you are drafting polylines make the most sense. When I am drawing a foundation plan that isn't a perfect rectangle you just draw one edge as a polyline and then offset the width of the wall. and that's only the first example that came to mind. |
Posted By: Kent Cooper
Date Posted: 05.Aug.2013 at 17:28
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In addition to things already mentioned....
Another reason for creating the Polyline entity type back when they first came into the picture was to save memory. (Memory was expensive in those days, but it doesn't matter so much today.) A Polyline holds information about its Layer, linetype, linetype scale, color, thickness, lineweight, and so on, once for the whole Polyline, no matter how many segments it contains. The same construction, using independent Lines and Arcs, would need to keep track of all that information separately for every entity, and would thereby consume more memory.
Polylines with non-continuous linetypes can (optionally) have the generation of the linetype pattern flow around the corners / across the vertices, so that the linetype will be apparent even on something made up (entirely or in part) of segments that are too short for the linetype to show if they were independent Lines and Arcs.
Suppose you have an outline of some kind made up of Lines, and you want all the corners rounded. You would need to Fillet each corner separately, picking on two Lines for each corner. With a Polyline, you can use the Polyline option in the Fillet command, and it will round all the corners (details of geometry permitting) with just one pick anywhere on the Polyline.
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