Graphics Programs Reference
In-Depth Information
Figure 9-3:
To make an omelet, sometimes you have to break a few ellipses.
Splines: The sketchy, sinuous curves
Most people use CAD programs for precision drawing tasks: straight lines, carefully
defined curves, precisely specified points, and so on. AutoCAD is not the program to
free your inner artist — unless your inner artist is Mondrian. Nonetheless, even meticu-
lously created CAD drawings sometimes need freeform curves. The AutoCAD
spline ob-
ject
is just the thing for the job.
You can use AutoCAD splines in two ways:
Eyeball the location and shape of the curve and don't worry too much about get-
ting it just so. That's the freeform, sketchy, not-too-precise approach that I de-
scribe in this section.
Specify their control points and curvature characteristics precisely.
Beneath their easygoing, informal exterior, AutoCAD splines are really highly
precise, mathematically-defined entities called
NURBS curves
(NonUniform Ration-
al B-Spline curves). Mathematicians and some mechanical and industrial design-
ers care a lot about the precise characteristics of the curves they work with. For
those people, the AutoCAD SPLINE and SPLINEDIT commands include a number of
advanced options. Look up
spline curves
in the AutoCAD online help if you need
precision in your splines.
Drawing splines is straightforward, if you ignore the advanced options. The following
procedure draws a freeform curve with the SPLINE command:
