Mathematically this corresponds to the limit of an infinite radius of curvature.

During further analysis it should be assumed that the phasor travels times clock-wise along a semicircle of infinite radius.

Several properties hold for the plane which can be thought of as a sphere with infinite radius.

The reference point for this potential is a theoretical hollow conducting sphere, of infinite radius, centered on the conductor.

Zero curvature gives a line (circle with infinite radius).

In this sense a line is a generalised circle of infinite radius.

A straight line can be defined as a curve of infinite or very large radius.

A polytrope with index has an infinite radius.

These lines are sometimes thought of as circles through the point at infinity, or circles of infinite radius.

Only now think of it as a sphere with an infinite radius.