[PROJ] "Local" projection method?

[Javier Jimenez Shaw]

Using "Orthographic" instead of "Local" seems to work. At least returns
some values that make sense.
However the parameter "Azimuth" is not used. Is there any reason for that?
I was expecting just a rotation of the input before continuing with the
transformation.

Thanks
.___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
Entre dos pensamientos racionales
hay infinitos pensamientos irracionales.



On Thu, 24 Sep 2020 at 11:01, Even Rouault <even.rouault at spatialys.com>
wrote:

> On jeudi 24 septembre 2020 05:42:22 CEST Kristian Evers wrote:
>
> > Nyall,
>
> >
>
> >
>
> > >
>
> > > Based on this, would it be appropriate to directly map this projection
>
> > > method across to the "Orthographic" method? Or am I missing something
>
> > > important?…
>
> >
>
> >
>
> > Yes, it would seem so. Be aware though, the current Orthographic
> projection
>
> > implementation in PROJ is only valid in the spherical case. You would
> have
>
> > to extend that to the ellipsoidal case for the mapping described by
> Esri.
>
> > We’ve got an old issue [0] which contains some hints on how to go about
>
> > that.
>
>
>
> "Recent" EPSG guidance note 7.2
>
>
>
>
> https://drive.tiny.cloud/1/4m326iu12oa8re9cjiadxonharclteqb4mumfxj71zsttwkx/62018e48-9da4-43e7-b598-1202cd96ec9f
>
>
>
> (link got from epsg.org)
>
>
>
> has the maths for the ellipsoidal formulation of the orthographic
> projection in paragraph 3.3.5, page 89
>
>
>
> I cannot comment on the full equivalence of the "Local" projection, but
> hopefully in the Scale_Factor=1 + Azimuth=0 case, they would match.
>
>
>
> One way to check that the theory local = ortho on the sphere is valid
> would be to use ArcGIS with a sphere as the ellipsoid and compare results
> with +proj=ortho
>
>
>
> Other point:
>
> Looking at
>
> https://pro.arcgis.com/en/pro-app/help/mapping/properties/orthographic.htm
> ,
>
> there's the Auxiliary Sphere Type parameter that can be used to change how
> orthographic is computed on an ellipsoid, but I'm not sure any of the
> listed method is equivalent to the ellipsoidal formulation from EPSG, as
> the ellipsoidal formulation from EPSG doesn't seem to use authalic latitude.
>
>
>
>
>
> Even
>
>
>
> --
>
> Spatialys - Geospatial professional services
>
> http://www.spatialys.com
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