links for 2010-01-07

In mathematics, a spherical coordinate system is a coordinate system for three-dimensional space where the position of a point is specified by three numbers: the radial distance of that point from a fixed origin, its elevation angle measured from a fixed plane, and the azimuth angle of its orthogonal projection on that plane, measured from a fixed reference direction on the same. The elevation angle is often replaced by the inclination angle measured from a zenith direction perpendicular to the reference plane.