[PROJ] Relevant descrepancies between Sinusoidal and Homolosine

[Luí­s Moreira de Sousa]

Hi again Even, apologies for insisting. In the .ods I sent earlier you can verify that the Homolosine is preserving the northing-latitude identity, even with the ellipsoid. And also that it does not match the Sinusoidal.

My guess is that the Homolosine is already spherical-spherical as it is. Note that I am still using PROJ 5.2.

Thank you.

--
Luís

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, March 10, 2020 1:55 PM, Even Rouault <even.rouault at spatialys.com> wrote:

> On mardi 10 mars 2020 12:42:15 CET Luí­s Moreira de Sousa wrote:
>
> > Hi Even,
> > I have not yet checked the formulas from that source, but regarding the
> > current Homolosine implementation, its outputs are the expected. So perhaps
> > it is applying the spherical Sinusoidal and the ellipsoidal Mollweide?
>
> No, before my PR, that would be the reverse: it would apply the ellipsoidal
> Sinusoidal and the (spherical, but there's only spherical implemented)
> Mollweide. igh doesn't do real computations by itself: it just dispatches to
> the existing sinu or moll methods depending on the input coordinate.
>
> Maybe, a proper fix would probably be add an ellipsoidal formulation to
> Mollweide. But igh would then be much more complicated because the dispatching
> logic strongly relies on the fact that there's an identity between northing
> and latitude from what I can see.
>
> So I guess making sure igh uses spherical formulas for both sinuosidal and
> mollweide, as I intented in my PR, is probably better than the current
> situation where there's a mix ?
>
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