Oups!!!!!!!! I was totally wrong in one of my statement in my previous email.
Matthias spotted my error and my correction is below (after the 2nd quoted
text).
Matthias Basler a écrit :
> An interesting approach and certainly a good idea. I have two questions here.
>
> 1. Will this result in an API change or will the combinations of the affine
> transformations be done "behind the changes" from my point of view as an
> developer using GeoAPI interfaces to getting conversions done?
For those using GeoAPI interfaces, there is absolutly no API change. Same for
GeoTools API outside the org.geotools.referencing.operation.projection package.
For those who created their own MapProjection implementations, those one will
need to change their implementation. But I think that there is few of them.
> You are surely deeper in that matter than me, but somehow the idea that that
> a conversion of coordinates between two UTM stripes is a matter of a affine
> transform contradicts my picture and understanding of those projections:
Yes you are right and this part of my email was wrong.
What I said is true for the Mercator projection (and I tested it with different
standard parallels). I said the same for TransverseMercator without testing it,
and forgot that between the two UTM projections there is an affine transform
performing the change of central meridian. What I told was true for the case
where the affine transform between two projection collapse to the identity
transform, which is not the case between UTM because of that translation term.
The geotidy implementation is correct and inserts that translation affine
transform as expected between the two UTM. Only my own unchecked extrapolation
in my email was wrong. My distraction to blame here.
Best regards,
Martin
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