rho
Distance from the origin to the point. It is always zero or positive.

Learning Mission
Move a point in 3D space and see how distance, turn-around angle, and down-from-the-top angle describe its position.
Distance from the origin to the point. It is always zero or positive.
The rotation angle around the xy-plane, measured from the positive x-axis.
The angle from the positive z-axis down toward the point.
Enter x, y, and z to convert back to spherical coordinates.