[Gvsig_english] Fwd: Projections for Portugal

[Antonio Falciano]

Il 28/06/2017 12:19, Associação de Municípios TERRAS DO INFANTE ha scritto:
>
> ---------- Forwarded message ----------
> From: *Associação de Municípios TERRAS DO INFANTE* <gtf.lagos at gmail.com
> <mailto:gtf.lagos at gmail.com>>
> Date: 2017-06-27 16:42 GMT+01:00
> Subject: Projections for Portugal
> To: cordinyana at gvsig.com <mailto:cordinyana at gvsig.com>
>
>
> HI,

Hi,

> I just downloaded your testing version, build 2827, and found that ESRI
> projection 102164 is being interpreted by gvSIG as EPSG:5018, which is
> an error.

I'm agree, it's a wrong assumption based on SRS name similarity.

> In fact, ESRI:102164 shall be interpreted by gvSIG as EPSG:20790.

Geodesically speaking, ESRI:102164 and EPSG:20790 are two different
SRSs, even if they looks very similar, for two reasons: firstly they
adopt different prime meridians (respectively Greenwich and Lisboa),
secondly ESRI:102164 doesn't consider the transformation parameters
towards WGS84 (like all ESRI SRSs and it was in the past for all prj).
So gvSIG doesn't relate them correctly, because they're not equivalent
in Geodesy.
Operationally speaking, instead, because their projected coordinates are
the same, the user could set EPSG:20790 manually at the moment, as
Mario has well explained in the previous email.
It's clear that projection file recognition in gvSIG could be further
improved including also ESRI codes, but the transformation parameters
would be missing in that case. So I think that ESRI codes should be
remapped as EPSG ones in order to take full advantage of transformation
parameters and avoid unwanted data shifts.

Cheers,
Antonio

-- 
Antonio Falciano
http://www.linkedin.com/in/antoniofalciano