TABLE OF CONTENTS The nurbs-based curves introduced several releases ago were a welcome addition. No more makeshift ellipses or splines now you can have the real thing. The ellipses and splines of previous AutoCAD versions were merely approximations, comprised of polyline and polyarc segments. Manipulating the segments or grabbing key geometric points was difficult. Now AutoCAD incorporates nurbs mathematics and algorithms into its functionality to generate true ellipses and splines. These ellipses and splines also use less disk space and memory than the polylines of previous releases.
Nurbs stands for nonuniform rational basis splines (simply called B-splines). The nonuniform nature of the splines permits the uneven spacing of knots, should you need to create a sharp curve. The rational basis permits regular geometry, such as arcs and ellipses, to be combined with the irregular free-form curves. B-spline refers to the precise curve-fitting ability generated from data points (thanks to Bezier).
The following command creates an ellipsis.
<span class="fixed">Command: ELLIPSE</span><span class="fixed">Arc/Center/:</span> pick one axis endpoint<span class="fixed">Axis endpoint 2:</span> pick the second<span class="fixed"> /Rotation:</span> select the other axis distance
The new ellipse command still has the Center, Axis, and Rotation option from the old ellipse command. When creating an elliptical arc, first define an entire ellipse, then indicate the starting and ending points of the desired arc.
<span class="fixed">Command:</span> ellipse<span class="fixed">Arc/Center/: a</span><span class="fixed"> /Center:</span> pick one axis endpoint<span class="fixed">Axis endpoint 2:</span> pick the other axis endpoint<a name="408"></a><a name="IDX-136"></a><span class="fixed"> /Rotation:</span><span class="fixed">Parameter/ :</span> pick the starting point of the arc<span...
