how do I convert a polygon to a polyline?

[atari2600]

Maybe I am missing something, but there's got to be a way to quickly convert a polygon into a polyline. I know the answer is probably obvious, and quite simple and yet I have simply overlooked it for the past several years.

Any suggestions? Help is greatly appreciated.

Thanks,

[CipesDesign]

Interesting question Matt. As far as I know, unless you can code it with vectorscript there isn't any way to do it. The only way I can seem to figure is to trace over it with the polyline tool. Pretty easy, unless it's got a bizillion vertices.

I'm curious: why do want to convert it? Is there something you need to do to it that you can't do to a polygon?

Also intetesting is the fact that you *can* convert a polyline to a polygon....

Also interesting that every so often, when performing ADD/CLIP SURFACE commands with polygons, the resulting shape ends up as a polyline (which I almost always convert back to a polygon)...

[Guest]

If you have a polygon and want a polyline AND you can afford to have one edge invisible, use the 2D reshape tool to hide one of the edges. The polyGON is then a polyLINE.

(Don't ask how I discovered this ... )

[jan15]

Polylines can have curved edges and hidden edges, while polygons can't. Is that why you want to convert? But you can hide an edge of a polygon, using the 2D Reshape tool, or add a curve to a polygon, using the 2D Reshape tool or the Add or Clip Surface tools. In either case it automatically becomes a polyline.

If you're concerned about exporting, I think they both export as polylines, because Autocad doesn't have a Polygon entity type.

[eas]

Katie, how does one hide the edge of a polygon with the 2D reshape? I did a little investigating and can't figure it out.

thanks

[Guest]

The 5th mode in the mode bar allows you to hide an edge of the polygon.

Click on the center (or midpoint) of the segment you want to hide and it then becomes hidden.

[atari2600]

On my 2d elevations, I use a polyline as the grade line. I like it because I can put the grade "in front" of my house. I usually have two to three edges hidden. I find this faster than clipping my house to the slope of the grade line. I usually do a polyline from scratch, but I inherited this particular elevation with a rather large polygon and was looking for a quick way to convert it without having to re-draw it. I find polylines to be extremely versatile.

[atari2600]

thanks Katie,

I just figured it out.

[P Retondo]

Polylines can contain arcs and other mathematically-defined curves, polygons can consist only of line segments. That appears to be the most essential difference between the two, and, like a broken glass, polylines can be converted to polygons with a bunch of little line segments approximating the curve, but not vice-versa.

Either can suppress the display of an edge using the 2d reshape tool. Select the rightmost mode on the tool options bar at the top of the screen (icon looks like a horizontal stick person, headless and with an arrow for a torso). When you get the hollow triangle cursor, click to make the edge disappear.

[Guest]

Pete - that's a great explanation of the icon.

[nicolas d]

katie,

if the entity in question is a polygon and looks like it has curves, making it a polyline by hiding one of its edges will not change the fact that the curves were made of hundreds (or thousands) of little lines.

like pete says, polylines can have arcs, polygons can't. an arc can be broken into lines (something generally not very good for a drawing) but those lines which form a faceted arc cannot be recombined into an arc.

if i need to separate a polyline in parts i'll use 'convert to lines' or 'decompse' indistinctly if it doesn't have any arcs, or 'decompose' exclusively if it does. i'm not sure i remember exactly in which cases (that's how it is with these things) but sometimes i find it useful to decompose a polyline in order to do something with its parts and then recompose it.

another thing that's nice is that clipping a polyline with curves doesn't make it a polygon. i seem to remember that in previous versions of VW it did.

[Jonathan Pickup]

nicolas, how did you get this polygon in the first place?