[gdal-dev] EPSG:2065 / South-oriented Krovak support (Czech friends thoughts wanted !)

[Even Rouault]

Le vendredi 29 janvier 2016 16:24:00, Daniel Fenton a écrit :
> Even,
> 
> I'm not sure if this helps, 

Me neither ;-), but thanks for jumping into this.

> but in dealing with an issue with WKID 5514,

EPSG:5514 is east-north oriented (like EPSG:5221, the GIS friendly equivalent 
of EPSG:2065), so it is naturally dealt with by proj.4.

> this WKT workers to properly convert data from WGS84. This was confirmed
> against a customer's source data.

Hum seing stuff like
PARAMETER["X_Scale",-1],PARAMETER["Y_Scale",1],PARAMETER["XY_Plane_Rotation",90] 
I'm not sure which projection engine is used behind. Such parameters aren't 
needed with proj.4 since AFAIU it naturally expects easting,northing 
coordinates to be provided as input for the +proj=krovak method (this must be 
the implementation of the "Krovak (North Oriented)" / EPSG:1041 method rather 
than original Krovak south/west oriented)

(funnly looking at the source of a PJ_krovak.c, I see there's a "+czech" 
parameter that can be provided to reverse the signs of x/y . hum....)

> '
> PROJCS["S-JTSK_Krovak_East_North",GEOGCS["GCS_S_JTSK",DATUM["Jednotne_Trigo
> nometricke_Site_Katastralni",SPHEROID["Bessel_1841",6377397.155,299.1528128
> ]],TOWGS84[589,76,480,0,0,0,0],PRIMEM["Greenwich",0],UNIT["Degree",0.017453
> 292519943295]],PROJECTION["Krovak"],PARAMETER["False_Easting",0],PARAMETER[
> "False_Northing",0],PARAMETER["Pseudo_Standard_Parallel_1",78.5],PARAMETER[
> "Scale_Factor",0.9999],PARAMETER["Azimuth",30.28813975277778],PARAMETER["Lo
> ngitude_Of_Center",24.83333333333333],PARAMETER["Latitude_Of_Center",49.5],
> PARAMETER["X_Scale",-1],PARAMETER["Y_Scale",1],PARAMETER["XY_Plane_Rotation
> ",90],UNIT["Meter",1],AUTHORITY["EPSG","102067"]] '
> 
> Daniel
> 
> *Daniel Fenton*
> *Software Engineer | Esri R&D*
> *https://koopjs.github.io <https://koopjs.github.io>*
> On Thu, Jan 28, 2016 at 12:05 PM Even Rouault <even.rouault at spatialys.com>
> 
> wrote:
> > Hi,
> > 
> > I'm having a look at the following all related issues :
> > https://trac.osgeo.org/postgis/ticket/1940
> > https://trac.osgeo.org/proj/ticket/185
> > https://trac.osgeo.org/gdal/ticket/4762
> > 
> > related to EPSG:2065 support, ie "S-JTSK (Ferro) / Krovak". There's an
> > issue
> > about the datum shift used, but that's an easy one compared to a more
> > serious
> > one regarding axis order.
> > 
> > The proj.4 krovak method expects the first value of a coordinate pair to
> > be a
> > easting, and the second value a northing. Whereas original Krovak
> > (EPSG:2065)
> > is supposed to be southing first, westing second.
> > 
> > https://trac.osgeo.org/gdal/ticket/4762 suggests to add a "+to_meter=-1"
> > parameter. Which means that the coordinates supplied are first westing,
> > second
> > southing (instead of "+to_meter=-1", a cleaner equivalent way is to use
> > "+axis=wsu", meaning westing,southing,up )
> > But EPSG would mandate southing,westing.
> > 
> > But admitedly, for less exotic coordinate systems with official EPSG axis
> > order
> > latitude,longitude (EPSG:4326...) or northing,easting (some Finland
> > projected
> > CRS for example) we have never introduced in GDAL WKT or proj.4 strings
> > the +axis option, and the application/user does the coordinate switch
> > itself before passing that to GDAL/proj.
> > 
> > So, does that sound OK that a user providing coordinates advertized to be
> > in
> > EPSG:2065 does that in westing, southing order ? Or was this something
> > particular to this user ? (I'd note that the dataset mentionned in the
> > ticket
> > is a GML resulting from a WFS server, and we all know the axis ordering
> > issues
> > related to WFS)
> > 
> > What a mess...
> > (Using EPSG:5221 which is the easting, northing variant avoids those
> > headaches)
> > 
> > Even
> > 
> > --
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