information:extraction
Clelia curves

Another kind of spherical spiral is the Clelia curve, for which the longitude (or azimuth) φ {\displaystyle \varphi } and the colatitude (or polar angle) θ {\displaystyle \theta } are in a linear relationship, φ = c θ {\displaystyle \varphi =c\theta }. Clelia curves project to straight lines under the equirectangular projection. Viviani's curve (c = 1 {\displaystyle c=1}) is a special case. Clelia curves approximate the ground track of satellites in polar orbit.