set object <index> circle {at|center} <position> size <radius> {arc [<begin>:<end>]} {<other-object-properties>}
The position of the circle is specified by giving the position of the center
center followed by the radius. The keywords at and center are synonyms.
The position and radius may be given in x-axis, graph, or canvas
coordinates. See coordinates (p. ). In all cases the radius is calculated
relative to the horizontal scale of the axis, graph, or canvas. Any
disparity between the horizontal and vertical scaling will be corrected for
so that the result is always a circle. If you want to draw a circle in plot
coordinates (such that it will appear as an ellipse if the horizontal and
vertical scales are different), use set object ellipse instead.
By default a full circle is drawn. The optional qualifier arc specifies a starting angle and ending angle, in degrees, for one arc of the circle. The arc is always drawn counterclockwise.
See also set object ellipse (p. ).