[Proj] EPSG-Code Definition for MGI

[Even Rouault]

Le lundi 02 novembre 2015 15:35:11, Dirk Peinelt a écrit :
> Yes, the same as spatialreference.org with 7-point-setting. (towgs84)
> But in proj.4 there is a another definition string in ./nad/epsg

The definisions are equivalent. Datum hermannskogel is hardcoded in proj.4 
source as being Bessel 1841 ellipsoid with following TOWGS84:

src/pj_datums.c:{"hermannskogel",  
"towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232",

The fact that you have either one or another one depends on how GDAL had been 
configured to produce the proj EPSG file, either requesting proj to do the datum 
expension, or keeping its name. But results should be identical.

$ gdaltransform -s_srs EPSG:4326 -t_srs "+proj=longlat +ellps=bessel 
+towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232 +no_defs"
10 50
10.0004366888121 50.0009092520235 -45.3904842091724
^C

$ gdaltransform -s_srs EPSG:4326 -t_srs "+proj=longlat +datum=hermannskogel 
+no_defs"
10 50
10.0004366888121 50.0009092520235 -45.3904842091724
^C

Even

> 
> //dirk
> 
> ----- Ursprüngliche Nachricht -----
> Von: "Markus Neteler" <neteler at osgeo.org>
> Gesendet: ‎02.‎11.‎2015 15:02
> An: "PROJ.4 and general Projections Discussions" <proj at lists.maptools.org>
> Betreff: Re: [Proj] EPSG-Code Definition for MGI
> 
> On Mon, Nov 2, 2015 at 1:09 PM, Dirk Peinelt <dirk.peinelt at t-online.de> 
wrote:
> > Hello,
> > the EPSG-code definitions for 31256 - 31258 (MGI = Austrian date) on the
> > master are different with spatialreference.org.:
> > 
> > https://github.com/OSGeo/proj.4/blob/master/nad/epsg/
> > http://spatialreference.org/ref/epsg/31256/proj4/
> > http://spatialreference.org/ref/epsg/31257/proj4/
> > http://spatialreference.org/ref/epsg/31258/proj4/
> > 
> > Could be here a bug in proj.4 EPSG database?
> 
> To my knowledge http://spatialreference.org is rather dated (on the
> respective OSGeo server I see only file timestamps older than several
> years).
> 
> Alternative:
> http://epsg.io/31256
> etc. Does this fit better?
> 
> best.
> Markus
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