What functions are available to support working in spherical coordinates, e.g., transforming (x, y, z) on a unit sphere to (longitude, latitude) and vice versa? More generally, is anything available on quadratic regression, i.e., obtaining a least squares solution to a system of n equations quadratic in 3 unknowns? The sum of squares of residuals (SSE) can have either one or two local minima. With polar coordinates, I can tell if a solution is unique and find the other solution if it is not. I can write my own, but I'd rather use more standard utilities if they exist. Thanks, Spencer Graves