where ax and ay are the transverse, equatorial radii (along the x and y axes) and b is the conjugate, polar radius (along the z-axis), all of which are fixed positive real numbers determining the shape of the ellipsoid (traditionally, ax and ay are denoted as a and b, respectively——thereby defining the equator as an ellipse——and b as c; however, in most cases——such as Earth——the equator is considered spherical, with the equatorial radius being defined simply as a and the polar as b——like an ellipse——thus a,b,c notation can be needlessly confusing).