Curved objects include arcs, circles, polyline arcs, donuts, ellipses, and splines.
Arcs--You can create arcs by specifying any three points.
Circles--You can create circles by specifying the center and the radius. In addition to this default method, you can specify two points to define the diameter, three points that define the circumference, or two tangent points and the radius.
Polyline Arcs--Multi-segmented polyline arcs provide editing capabilities unavailable for single arcs, as you can adjust their width and curvature. When you draw arc segments in a polyline, the first point of the arc is the endpoint of the previous segment.
Donuts--Donuts appear as filled rings or sold-filled circles; they are actually closed polylines with width.
Ellipses--The shape of an ellipse is determined by two axes that define its length and width. The longer axis is called the major axis; the shorter axis is called the minor axis.
Splines--A spline is a smooth curve that passes through or near a set of points that influence the shape of the curve. You can create or edit splines using either control vertices or fit points.
Helixes--A helix is an open 2D or 3D spiral. You can use a helix as a path along which to sweep an object to produce an image. For example, you might sweep a circle along a helix path to create a sold model of a spring.