[Proj] Normal vector to a point on an Earth ellipsoid

[Gerald I. Evenden]

On Tuesday 03 February 2009 10:54:22 am Ung wrote:
> Hi All,
>
> Is there a function within Proj4 that would return a representation of a
> normal vector to a point on an Earth ellipsoid? Perhaps something like:
>
> getNormal( projPJ my_cs, double x, double y, double z )
>
> Would be grateful for any clues!
> -ung

Sounds like an ENU coordinate but that is *not* part of a projection 
operation.  I will probably put a function like that in my geodesy library 
but it is more related to XYZ geocentric system with a translation rotation 
involved---translation of the geocentrin origin to a local point and rotation 
about this point.

But an ENU has *nothing* to do with projections as the XY (Easting-Northings)  
in projections have no relationship to the XY in EN even though the EN stands 
for Easting-Northing.

It is unfortunate that the ENU designers stole the projected space 
nomenclature.

If you are just concerned with a z value you would have to "pass it around" 
the projections operation.

-- 
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist