A line or direction from the center (principal point, isocenter, nadir point, or substitute center) to any point on a photograph.

For a plane curve C, the locus of end points of lines, drawn from a fixed point, that are equal and parallel to the radius of curvature of C.

One of a number of radial lines of position defined by an azimuthal radio navigation facility and identified in terms of the bearing (usually magnetic) of all points on that line from the facility.

Directed or diverging from a center.