Conical surface

In geometry, a conical surface is an unbounded three-dimensional surface formed from the union of infinite lines that pass through a fixed point and a space curve.

A (general) conical surface is the unbounded surface formed by the union of all the straight lines that pass through a fixed point — the apex or vertex — and any point of some fixed space curve — the directrix — that does not contain the apex.

[1] In general, a conical surface consists of two congruent unbounded halves joined by the apex.

Each half is called a nappe, and is the union of all the rays that start at the apex and pass through a point of some fixed space curve.

, and the apex is located on the circle's axis (the line that contains the center of

and is perpendicular to its plane), one obtains the right circular conical surface or double cone.

is an ellipse, or any conic section, and the apex is an arbitrary point not on the plane of