Drawing Curves - Mastering AutoCAD for Mac - page 469

TURNING OBJECTS INTO POLYLINES AND POLYLINES INTO SPLINES
At times, you'll want to convert regular lines, arcs, or even circles into polylines. You might want to
change the width of lines or join lines to form a single object such as a boundary. Here are the steps
to convert lines, arcs, and circles into polylines:
1 . Choose Modify  Object  Polyline, or type PE ↵ at the Command prompt.
2 . At the Select polyline or [Multiple]: prompt, pick the object you want to convert.
3 . At the prompt
Object selected is not a polyline. Do you want to turn it into one? <Y>:
press ↵. The object is converted into a polyline.
If you want to convert several objects to polylines, type M ↵ at the Select polyline or
[Multiple]: prompt, then select the objects you want to convert. You will see the Convert
Lines, Arcs and Splines to polylines [Yes/No]? <Y>: prompt. Type Y ↵, and all the
selected objects are converted to polylines. You can then go on to use other Pedit options on the
selected objects. If you want to convert a circle to a polyline, first break the circle (using the Break
tool on the Tool Sets palette) so it becomes an arc of approximately 359°.
To turn a polyline into a true spline curve, do the following:
1 . Choose Modify  Object  Polyline, or type PE ↵. Select the polyline you want to convert.
2 . Ty p e S ↵ to turn it into a polyline spline, and then press ↵ to exit the Pedit command.
3 . Click the Spline tool on the Tool Sets palette or type SPL ↵.
4 . At the Specify first point or [Method/Knots/Object]: prompt, t ype O ↵ for the Object
option.
5 . At the Select spline-fit polyline: prompt, click the polyline spline. Although it may
not be apparent at first, the polyline is converted into a true spline.
You can also choose Modify  Object  Spline (or enter SPE ↵) to edit a polyline spline. If you do,
the polyline spline is automatically converted into a true spline.
If you know you'll always want to convert an object into a polyline when using Pedit, you can turn on
the Peditaccept system variable. Enter PEDITACCEPT ↵ at the Command prompt, and then enter 1 ↵.
Using True Spline Curves
So far, you've been working with polylines to generate spline curves. The advantage of using
polylines for curves is that they can be enhanced in many ways. You can modify their width, for
instance, or join several curves. But at times, you'll need a more exact representation of a curve.
The spline object, created by choosing the Spline tool on the Tool Sets palette, produces a
more accurate model of a spline curve in addition to giving you more control over its shape.
The spline objects are true Non-Uniform Rational B-Spline (NURBS) curves . A full description
of NURBS is beyond the scope of this topic, but basically, NURBS are standard mathematical
forms used to represent shapes.