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I had occasion to want to convert a Circle to a circular Polyline [so I could give it width, but I can imagine other reasons to want to do that]. Since Pedit won't do that conversion with a Circle as it will with a Line or an Arc, I looked for a routine here [assuming I would need to do this again from time to time], that would do the conversion by a simple selection of the Circle, so I didn't have to go through all the steps needed to construct an equivalent Polyline over the Circle and then erase the Circle. I found some things that were prior to the existence of Lightweight Polylines, and/or that didn't take into account different Coordinate Systems, or a locked Layer, or non-default overrides of color, linetype, etc.
So I made one, and while I was at it, made one to go the other way -- convert a circular Polyline (Donut) into a Circle. [I also found something here to do that, but along with the shortcomings above, it also didn't quite determine whether the selected Polyline is actually circular in Donut-like fashion.] The Polyline-to-Circle converter works with either heavy or lightweight circular Polylines, and if the selected one has a global non-zero width, the User gets the choice of whether to draw the Circle along the Polyline's center-line or along its inside or outside edge. It even saves that choice to offer as a default on further use.
CirclePolylineSwap.lsp contains two commands: C2P [= Circle To Polyline] and P2C [= Polyline To Circle]. I hope others will find them useful.
Kent Cooper, AIA 
Upgraded version.
The original didn't undo as you'd expect, which I've fixed. There's nothing different about the operation of the commands.
Kent Cooper, AIA
Hi Kent,
Nice work 
A suggestion: you can use the following ssget mode to prompt for single selection (with behaviour akin to entsel), whilst excluding objects on locked layers:
(ssget "_+.:E:S:L")
Lee
@Anonymous wrote:....Dual monitor system, is there a setting to control which monitor it "sits" in upon opening each time. ....
I can't help you there -- I only have a single monitor.
Kent Cooper, AIA
@Lee_Mac wrote:....
A suggestion: you can use the following ssget mode to prompt for single selection (with behaviour akin to entsel), whilst excluding objects on locked layers:
(ssget "_+.:E:S:L")....
That looks potentially very useful. But I can't find any documentation about use of the underscore or plus sign or period or :L parts of it in the AutoLISP Reference or AutoLISP Developer's Guide. Can you explain what those parts do, whether the order of them matters, etc., or point me to something that does?
Kent Cooper, AIA
@Kent1Cooper wrote:That looks potentially very useful. But I can't find any documentation about use of the underscore or plus sign or period or :L parts of it in the AutoLISP Reference or AutoLISP Developer's Guide. Can you explain what those parts do, whether the order of them matters, etc., or point me to something that does?
The Help files don't document everything 
Attached is my personal reference for ssget, using information collected from various places. Note that some modes do not work with all versions and some are temperamental - but I'll let you experiment for yourself.
Lee
BTW, what's with the smiley's appearing in code blocks? I thought that was exactly what the code blocks were meant to prevent happening?
@Lee_Mac wrote:BTW, what's with the smiley's appearing in code blocks? I thought that was exactly what the code blocks were meant to prevent happening?
Even there you're not safe.... But if you're signed in and have your Settings right, you won't see the ones that are caused by colon-letter combinations anywhere, inside or outside code blocks. See
Kent Cooper, AIA
@Lee_Mac wrote:....The Help files don't document everything
Attached is my personal reference for ssget, using information collected from various places. Note that some modes do not work with all versions and some are temperamental - but I'll let you experiment for yourself.
....
Thanks for that great resource!
Kent Cooper, AIA
@Kent1Cooper wrote:Even there you're not safe.... But if you're signed in and have your Settings right, you won't see the ones that are caused by colon-letter combinations anywhere, inside or outside code blocks. See
That's disappointing - most other forums have this sorted 
But thanks for the link Kent
@Kent1Cooper wrote:
@Lee_Mac wrote:....The Help files don't document everything
Attached is my personal reference for ssget, using information collected from various places. Note that some modes do not work with all versions and some are temperamental - but I'll let you experiment for yourself.
....
Thanks for that great resource!
You're very welcome Kent
@lai wrote:....when i load my autocad with the lisp, i get this below error msg....
Regenerating model.
AutoCAD menu utilities loaded.
Type C2P to convert a Circle to its Polyline equivalent.
Type P2C to convert a circular Polyline to its Circle equivalent.; error: extra right paren on input
....
It doesn't do that for me. If you have it as a separate file loaded by something like acaddoc.lsp or an xxx.mnl file, or if you have included the two command definitions within some larger .lsp file, maybe there's something extra in the surrounding code.
The fact that it gives the prompts with the command names suggests that the appropriate code is loading -- do the commands work, despite the error message?
One test: load it separately from acaddoc.lsp or xxx.mnl or other means. Either type APPLOAD and navigate to CirclePolylineSwap.lsp to load it, or type
(load "CirclePolylineSwap")
If it doesn't give you the error message, then the error is somewhere in the surrounding code that's loading it.
Kent Cooper, AIA
@shashankabehera wrote:....I’m looking for some lisp which can convert Polygon to circle, Please find attached DWG file.
....
Those are octagons, made up of line segments. The P2C command is designed to convert actually circular Polylines, with two half-circle arc segments [such as Donut makes] to Circles.
Here's a really simple routine, which does not check whether the selected Polyline is a regular octagon, but leaves it to you to use it only on such objects:
(defun C:82C (/ oct); = Octagon-to-Circle
(vl-load-com)
(setq oct (car (entsel "\nSelect regular octagon to convert to Circle: ")))
(command
"_.circle"
"2P"
(vlax-curve-getStartPoint oct)
(vlax-curve-getPointAtParam oct 4)
); command
(entdel oct)
); defun
If you use it on other kinds of things, you may get a Circle out of it, depending on what it is and how it's configured, but it may not relate as you expect to the selected object. If you want it to be able to do polygons of other numbers of sides, or to check whether the selected Polygon is in fact regular, those can be done, but it would be a lot more complicated.
Kent Cooper, AIA
@shashankabehera wrote:Hi Kent,
Thanks for your prompt response. This routine is working fine.
I’ll appreciate if you can help me with the routine which can convert polygon of any no of sides to circle.
Well, it took a little trial and error to get it working as I wanted, but here's a routine. It could have been done sooner if it would merely handle a situation like your sample drawing, but I tried to make it as universal as possible.
The Pg2C command in the attached PolygonToCircle.lsp file converts any Polyline(s) [lightweight or heavy, 2D or 3D] that is closed, planar, has all straight segments of equal length, and all of whose vertices are the same distance from the center, including in different coordinate systems and with overrides of such things as linetype, color, etc.
As uploaded, it's set up to draw the CIRCUMscribing Circle(s) and to delete the polygon(s) that it converts, but it has instructions in it on what to do if you'd rather have it draw the INscribing Circle(s), and/or retain the polygon(s). [Maybe later I'll make those choices into options within the command, so you can have them either way without multiple files.]
Kent Cooper, AIA
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