How to offset a polygon?

[Anonymous]

Hey all,

I am currently learning AutoCAD as a student.  I have an assignment that is easy to grasp, but I am having a challenge in execution.  Basically, I have created the outline/permiter of a house floor plan.  It is a complex polygon with bumpouts, and insets. My challenge lies in the task of creating a 4" inside wall offset from the perimiter.  Please view my attachment for a view of what I am working on.

The drawing was created out of individual lines.  I have no problem offsetting these.  The issue lies in the fact that it is tedious and cumbersome to offset several dozen lines, and then have to tidy them up with trimming.  I thought that a far easier way would be to convert the individual lines into a polygon by grouping them, and then offset the grouped object.  I could not make this work for me.  I then experimented with an irregular object, created from a rectangle with a mitered corner.  I found that I could only offset this object if it was a polyline, and not grouped.  Here are some issues that are baffling to me:

• Does 'grouping' create a polygon?
• If I have a polygon, how do I change it to a polyline?
• Why am I able to offset a polyline object, but not an irregular object created by grouping lines?
• What is an efficient approach to my challenge, if my solution is sub-optimal?

Many thanks to all for any suggestions ...

[rkmcswain · Accepted solution]

1. No, grouping does not create a poly[line] (no such object as a polygon).

2. Again, there is no such object as a polygon. You can convert individual objects (lines and arcs) into a polyline using PEDIT or JOIN.

3. See #1.

4. Join the separate objects into a polyline, then offset. Be aware of the system variable OFFSETGAPTYPE ( http://help.autodesk.com/view/ACD/2017/ENU/?guid=GUID-EB2A74E1-E6C8-4690-9658-7F731AB7FD84 ) as this can affect the resulting offset entity.

[TheCADnoob]

Its hard to tell from the screen shot but it looks like you are going to have to clean up your drawing first. It looks like some lines are extending past others. If this is the case there may be other issues as well. All lines will need to be ended at the "vertex" of the other lines. 

Once that is done you can proceed as @rkmcswain suggested and join the lines into a poly line and then the offset can be don as one object as per the screen cast.

https://knowledge.autodesk.com/community/screencast/9d76669d-c6f1-495b-9f7c-43e3d1322044

[Anonymous]

Many thanks for the assistance - and the knowledge shared.  I used the join command as suggested, and obtained the desired results. Thanks as well for the terminology of poly -> gon vs. line.

I am curious to learn where, when, and why one would use the 'group' command?  I assume it would be especially handy when moving things around, is there any other use for it?

The screen capture was at fault for showing lines not properly intresecting.  I noticed that as well, and checked it out.  There was a dot next to the vertice. I am not at all certain why that dot is there, but I found it is occurs at random. Perhaps, and I am guessing here, it was created by an inadvertant mouse click when creating the original line?  The fact that it could be removed is significant, and tells me that I created it somehow.

Cheers all around ...

[TheCADnoob]

I frequently use group to repeatedly move lots of object simultaniously. its also handy to create a temporary block. Ive done it for quick sketches.

[sthompson1021]

rk wrote "2. Again, there is no such object as a polygon. You can convert individual objects (lines and arcs) into a polyline using PEDIT or JOIN."

Don't mean to nitpick but...

[pendean]

POLYGON is a command name, it draws closed PLINE object types

Same applies to DTEXT command for example, and a few dozen others.

[TheCADnoob]

you toatly beat me to it 🙂

[pendean]

Funny how we both opted for 6-sides and properties command 🙂

[Patchy]

Twin ?

[rkmcswain]

Come to think of it.... has anyone ever seen @pendean and @TheCADnoob at the same time? 

Maybe they are the same person.... Except they are both superheros..... not sure how that works.....

[sthompson1021]

Ah, my attempt at humor fell flat. I realize that the command POLYGON creates a closed pline. Says so right in the pic I posted. I'll try not to nitpick anymore 

[TheCADnoob]

Ha! Im just aspiring to greatness 🙂

[TheCADnoob]

the jig is up *swallows cyanide pill* tell the world my story...ackk...

[rkmcswain]

I wish there was a polygon object with properties and methods. They successfully went this route with arrays, but they failed on the revision cloud. So who knows.

[TheCADnoob]

moo moo. sometimes humor eludes me.