[Proj] What about datum shift via direct projection?
Gerald I. Evenden
geraldi.evenden at gmail.com
Mon Dec 15 20:47:17 EST 2008
On Monday 15 December 2008 3:53:24 pm ndzinn at comcast.net wrote:
> Thanks for these references on direct projection. Weird, yes, in the
> sense of unusual, but clever and useful for the reasons stated by the
> Regarding the least-squares adjustment for the new CM, scale on CM and
> false coordinates, linearization of the TM algorithm by Taylor expansion
> must be exceptionally ugly, but this can be simply accomplished numerically
> to achieve the same results.
I frankly do not see what is so clever about it. You can rubber sheet any 2D
surface onto another---even Mickey Mouse's face.
I did basically the same thing with MAPGEN. MAPGEN had no idea what
projection was involve as the "projection" operation in MAPGEN was carried
out with a polynomial approximation of the projection. Works fairly well for
large scale maps and is generally faster than cranking zillions of point
though a full precision TM projection.
The only problem is that one still needs all the parts to generate the
approximating rubber sheet. And an added problem: keeping an audit trail for
others to know what you did. Also, do others have your magic rubber sheet
evaluator or inverse operation capability?
Sorry, I have reservations about all this.
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
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