We begin our discussion of graphics primitives by discussing the drawing commands that make two-dimensional primitives appear on your computer screen. A new line will begin at the most recent to-point. Geometrically, this has the effect of closing the line figure to produce a polygon. If a LINE segment has been drawn erroneously and you want to erase it, enter LINE, then UNDO in the command window. The most recent segment drawn will be erased.
More complicated shapes are available, including circles and arcs, as follows.
A circle is formed in AutoCAD as a sequence of straight lines. Enough lines are used so that the viewer is tricked into believing that the smooth contour of a circle is present. Hence, the detail that is present as small straight lines in a many-sided polygon is not visible under most conditions. One's visual system therefore infers that such high-resolution polygons are circles. The pointing device cursor and the center point delimit the circle's radius.