Frequent tipster Danny Korem shares a procedure that will help in the creation of complex closed polylines in AutoCAD.
"Turning lines and arcs into polylines can be sometimes a tedious job. This especially applies to outer contours. The following steps will make it easier to create one:
- Get rid of zero-length geometry with the Purge command.
- Use the Overkill command to eliminate multiple identical vector segments.
- Select the geometry and verify (in the Properties window) that all the geometry resides in the same elevation ([Lines, Start Z, End Z both=0] [Arcs, Center Z=0] etc.).
- Create a bounding rectangle outside the existing geometry; use the BPoly command, and click on a point between the new rectangle and the existing geometry.
- It's most likely that two new polylines are created. Get rid of the two outer rectangles and enjoy."
Notes from Cadalyst Tip Patrol: Wow, that worked! Polylines are 2D objects — unless, of course, they are 3D polylines; there is a difference. We want to make a closed, 2D polyline. Even though lines, arcs, etc. look like they line up correctly, they often don’t. There are many reasons for this. You can start off using the PEdit (Polyline Edit) command and the Join option therein, but circumstances have to be just right in order for this to work. You can also use the BPoly (Boundary) command. This command creates a closed polyline in the way a hatch object is created. You choose a point, and it fills the area looking for edges. It will create a closed polyline around the selected perimeter.
Of course, everything must be just right for this to work, as well. I tested this tip on a project I was working on. I had followed steps one through three, but didn’t think of step four. I was still having trouble getting my linework to close. As instructed, I drew a rectangle around my linework, used the BPoly command, and bam — it made everything into two polylines. It made two because their ends were overlapping just enough to prevent it from closing. A quick fillet and we were done.