[Proj] Re: What proj library version is best?

[Thierry Laronde]

Hello,

On Thu, Jul 08, 2004 at 12:03:28AM +0200, Michel Wurtz wrote:
[..]
> the correct way to tranform UTM/WGS84 to NTF/Lambert coordinate is :
> 
> (E,N) UTM -> lat/long WGS84 -> X,Y,Z (tridimentional) -> Datum shift, rotation
> and scale from WGS84 to NTF -> lat/long NTF -> (E,N) Lambert.
> 

As already explained by Gerald Evenden and Paul Kelly, your
"transformation formula" is a typical pipe i.e. a combination of
different tools. Since the beginning and end
are reverse functions, they belong to the very same library: Gerald
Evenden's PROJ.4 or libproj4 (the new version).

The datum handling deserves its proper tools (library). The discussion
was not about user visible result, but how the code shall be organized.

GPL GRASS is already providing such tools (minus some problems in some
cases linked precisely to the fact that proj and datum are merged in a
library).
Since KerGIS is new I have the possibility (and the duty) to choose what
I think is the best way to implement features. This best is for me to
separate clearly pieces that are logically distinct, allowing to rectify
the curve of needs (approaching almost exactly a "spline" via the
smallest segments (programs)) and to insulate problems.
-- 
Thierry Laronde (Alceste)  <tlaronde at polynum.com>
http://www.kergis.org/  |  http://www.kergis.com/
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