How to Draw Ellipses in BricsCAD

Quick answer: The default way to draw an ellipse is to specify the endpoints of one axis, then a distance for half the length of the second axis. Whether BricsCAD creates a true ellipse or a polyline approximation of one depends on PELLIPSE, and editing an ellipse’s start and end angle fields can turn it into an elliptical arc, or back again.

The Geometry of an Ellipse

The endpoints of the first axis you specify determine the ellipse’s orientation. The longer axis is the major axis, the shorter one the minor axis, half of each being the major radius and minor radius respectively. It doesn’t matter which axis you define first, BricsCAD works out which is major and which is minor based on their actual lengths.

One term worth flagging: the source defines eccentricity here as the minor radius divided by the major radius, and states that a circle has an eccentricity of 1 under that definition. This is the opposite of the standard mathematical definition of eccentricity, where a circle is 0 and eccentricity approaches 1 as an ellipse gets more elongated. Whichever convention you’re used to, this is how Octave’s own documentation defines the term for this specific context.

Real Ellipses vs Polyline Representations

PELLIPSE controls whether BricsCAD creates a true ellipse or a polyline approximation instead. A real ellipse has five handles: its centre point, plus the endpoints of both axes. A polyline representation is a closed polyline built from arc segments instead, visibly different once you select it.

Finding the Ellipse Tool

The Draw menu, the Draw toolbar, the Draw ribbon panel, or the Draw tab of the No Selection Quad. Alternate methods live specifically in the Ellipse submenu of the Draw menu and the Ellipses toolbar.

Drawing an Ellipse: General Procedure

Launch ELLIPSE. You’re prompted for the first end of an axis, or to choose Arc or Center.
Specify a point. You’re prompted for the second end of that axis.
Specify a point. You’re prompted to set the other axis, or choose Rotation.
Specify a point. The ellipse is created.

Drawing an Elliptical Arc: General Procedure

An elliptical arc is just a portion of an ellipse.

Launch ELLIPSE. You’re prompted for the first end of an axis, or to choose Arc or Center.
Choose the Arc option. You’re prompted for the first end of an axis, or to choose Center.
Specify a point. You’re prompted for the second end of that axis.
Specify a point. You’re prompted to set the other axis, or choose Rotation.
Specify a point. You’re prompted for a start angle, or to choose Parameter.
Either type a value in the dynamic field, or click to specify the arc graphically. You’re prompted for an end angle, or to choose Parameter or Included angle.
Click a point. The elliptical arc is created.

Editing an Ellipse or Elliptical Arc

Select it; its properties appear in the Properties panel.
Type a new value into the Center, Major radius, Minor radius, Radius ratio, Start angle, or End angle field and press Enter.
Press Esc to stop editing.

Editing the Start angle or End angle field turns a full ellipse into an elliptical arc. Set both back to 0 to turn an elliptical arc back into a complete ellipse.

Frequently Asked Questions

Does a circle count as a special case of an ellipse in BricsCAD? Yes, under the source’s own definition of eccentricity here (minor radius divided by major radius), a circle has an eccentricity of 1, since both radii are equal.

What’s the visible difference between a real ellipse and a polyline representation? A real ellipse has five handles: its centre and the four axis endpoints. A polyline representation is a closed polyline made of arc segments instead, which you can see once you select it.

Can I turn an existing ellipse into an elliptical arc without redrawing it? Yes, edit its Start angle or End angle field in the Properties panel. Setting both back to 0 restores it to a full ellipse.

Does the order I specify the two axes in matter? No, BricsCAD automatically determines which axis is major and which is minor based on their actual lengths, regardless of which one you define first.