11.15 ellipse

Ellipses may be drawn on multiplot canvases using the ellipse command. The shape of the ellipse may be specified in many different ways, by specifying

beginenumerate the position of two corners of the smallest rectangle which can enclose the ellipse when its major axis is horizontal, together with an optional counter-clockwise rotation angle, applied about the center of the ellipse. For example:

ellipse from 0,0 to 4,1 rot 70

the position of both the center and one of the foci of the ellipse, together with any one of the following additional pieces of information: the ellipse’s major axis length, its semi-major axis length, its minor axis length, its semi-minor axis length, its eccentricity, its latus rectum, or its semi-latus rectum. For example:

ellipse focus 0,0 center 2,2 majoraxis 4
ellipse focus 0,0 center 2,2 minoraxis 4
ellipse focus 0,0 center 2,2 ecc 0.5
ellipse focus 0,0 center 2,2 LatusRectum 6
ellipse focus 0,0 center 2,2 slr 3

the position of either the center or one of the foci of the ellipse, together with any two of the following additional pieces of information: the ellipse’s major axis length, its semi-major axis length, its minor axis length, its semi-minor axis length, its eccentricity, its latus rectum, or its semi-latus rectum. An optional counter-clockwise rotation angle may also be specified, applied about either the center or one of the foci of the ellipse, whichever is specified. If no rotation angle is given, then the major axis of the ellipse is horizontal. For example:

ellipse center 0,0 majoraxis 4 minoraxis 4

Optionally, an arc of an ellipse may be drawn by adding the following modified:

arc from <angle> to <angle>

The line type, line width, and color of line with which the outlines of ellipses are drawn may be specified after the keyword with, as in the box and circle commands above. Likewise, ellipses may be filled in the same manner.

All vector graphics objects placed on multiplot canvases receive unique identification numbers which count sequentially from one, and which may be listed using the list command. By reference to these numbers, they can be deleted and subsequently restored with the delete and undelete commands respectively.