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Home > Draw > Ellipse: Center + Axes
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Ellipse: Center + Axes (tool)An ellipse from center, a major-axis point, and a minor-axis point.
Menu: Draw > Ellipse: Center + Axes | Node: Ellipse | In depth: Ellipses
Three clicks: the center, a point out along one axis, then a point that sets the other.
The second click does double duty. Its distance from the center is one radius, and its direction is the whole ellipse's orientation, so that click is where you decide which way the ellipse leans. Everything after it is measured against that.
The third click is a distance, not a position. Only its perpendicular distance from the first axis is read, so you do not have to find the far end of the second axis and click it exactly. Click anywhere that looks the right amount off the axis and the ellipse comes out that fat. This is the same idea as the third click on Rectangle: Directed, and it is worth knowing because aiming at a corner that does not exist is the slow way to work.
All three points stay live, and each one does a distinct job: move the center and the ellipse moves; move the second point and it rotates and changes one radius; move the third and it only changes the other radius.
The tool calls your second click the major axis and the third the minor one, and it does not check whether that is true. Click a short first axis and a long second one and you get a perfectly good ellipse whose so-called major axis is the shorter of the two.
Nothing downstream minds, but two things read those names, so it is worth knowing which is which: the Ellipse node labels its inputs the same way, and an Elliptical Arc measures its start and end around the ellipse from the major-axis direction. If an arc on an ellipse starts somewhere you did not expect, this is usually why.
An ellipse with either radius at zero is not a shape, so nothing is made. The tool simply waits for a third click it can use.
Points can ride on an ellipse like any other curve: drop one on it and it binds, sliding around the ellipse and following it when any of the three drivers moves.
< Previous: Compass: Radius | Next: Elliptical Arc >
- In the node graph: Ellipse - build the same ellipse as a node.
- Ellipses: how an ellipse is defined here and what it can carry.
- Elliptical Arc: a piece of one, and where its ends are measured from.