[Proj] WGS84 definition

[Frank Warmerdam]

On 12/5/05, Martin Vermeer <martin.vermeer at hut.fi> wrote:
> I suppose you are right -- where the current user base of PROJ4 is
> concerned. But I have been thinking if it would be possible to extend it
> by simple means to also serve geodetic uses, as that is what interests
> me. And the package has been moving from mere projections to geodetic
> datums and transformations anyway.

Martin,

As Cliff suggests, I think it is wrong to think there is some deep
attachment to geodetic concepts of what the different datums are.
PROJ.4 basically knows about ellipsoids, projections, and
"transformation methods" between datums.   When you say +datum=WGS84
in PROJ.4 it translates this into an ellipsoid definition and recognises that
to transform to WGS84 datum it can apply a 0,0,0 offset.  It doesn't really
know anything about geoid, or anything else.

We can try and other kinds of datum transformations but ultimately
a rigerous definition of datum does not existing in PROJ.4.  Only the
implicit definition of what it takes to convert to WGS84 (whatever
that is).

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent