Tip 2244: Polyline Subtract
Polyline Subtract came in from Peter Kitter -- with a little help from some online friends. The purpose of this routine is to automate the editing of a closed polyline border by subtracting regions defined by other closed polylines -- extremely useful for mapping and layout work. The result is a new polyline border comprised of the original border with modifications. The modifications are the intersecting closed borders broken apart and attached toward the inside of the original border. Thus, one polyline area is subtracted from another to create a new polyline. To use this tip, load the LISP code into AutoCAD and type Pls. First select the outside border polyline. You can select multiple polylines as outside borders. Next select the inside border polylines. The rest is automatic, although the process can take a few seconds depending on the complexity of the geometry. This problem isn't easy to define, yet the code is very straightforward. Nice job.