[Proj] The world of ECEF aka geocentric coordinates

[Duncan Agnew]

Bomford 4th edition, Appendix C gives the iterative formula, along with 
Bowring's approximation (adequate
on the Earth's surface). Pace Cliff, he uses "spheroid" for the generic 
surface, but restricted to flattened
ellipsoids rather than elongated ones (definition in Appendix A).

ECEF has meaning as a reference frame--Earth Centered Earth Fixed--but 
has no bearing on the types of coordinates used to denote a particular 
position--they might be spherical, ellipsoidal, or Cartesian. Strictly 
speaking, "geocentric" would be a subset of ECEF, since the reference 
frame used for satellite
orbits is also geocentric, but (partly) tied to inertial space rather 
than to the (average) Earth for its
orientation.

All the conversions being discussed are between coordinate triplets 
(Cartesion and ellipsoidal), and
have nothing to do with the reference frame, save that its origin is at 
the center of mass of a uniform
ellipsoid, and polar axis along its axis of symmetry. Maybe the 
conversion should just be labeled by
coordinate type?

Duncan Agnew