[Qgis-developer] Unexpected change in ESPG codes from shapefiles (in stable and dev)

[Leyan]

On 12/18/2014 06:35 PM, Kari Salovaara wrote:
> Hi,
>
> in Finland we have map datasets free of charge to download from The 
> National Land Survey of Finland (NLS). See 
> http://www.maanmittauslaitos.fi/en/opendata
> From Topographic Database You can download in ESRI shape format any 
> Finnish map area. In each area You'll get a number of shapefiles 
> related to category and each category has also a *.prj file.
>
> The problem arises when You make a layer from any of these shapefiles 
> in following example;
> 1. set project CRS to Finnish ESPG:3067 ( which is on the list 
> EPSG:3067 - ETRS89 / ETRS-TM35FIN)
> 2. make a layer from shapefile, as it has *.prj which starts like 
> PROJCS["ETRF89_ETRS_TM35FIN",GEOGCS["GCS_ETRS89",DATUM["D_ETRS_1989"....
> You expect the layer CRS to be 3067 but when You look to layer 
> properties it shows 3047 (in the dialog list EPSG:3047 - ETRS89 / 
> ETRS-TM35)
> (which means, I think, 
> PROJCS["ETRF89_ETRS_TM35",GEOGCS["GCS_ETRS89",DATUM["D_ETRS_1989")... 
> small but nasty difference.
>
> This problem can cause difficulties when creating scripts for 
> automation etc.
> And very odd is that when You have created an empty project with CRS 
> set to 3067 and create a shapefile its *.prj file starts 
> PROJCS["ETRS89_TM35FIN_E_N",GEOGCS["GCS_ETRS_1989",DATUM["D_ETRS_1989",
> but in this case the EPSG is 3067.
>
> For  my knowledge ETRS-TM35FIN is always and only EPSG:3067.
>
> Could someone explain is this failure in QGIS or GDAL/OGR or PROJ.4?
> This problem has been tested in 2.6.1 (latest update in OpenSuse12.3) 
> and 2.7.0 (nightly) versions and both linux and win 7 environments.
> Finnish QGIS society are waiting this Christmas Question answer with 
> interest. ;)
>
> With warm and kind regards,
> Kari
>
> PS. This has been discussed here locally without any final 
> understanding. Some guess has been that program only looks and takes 
> first some nearly suitable code and uses it.
>
It seems the proj4 string for both CRS is the same in my local 
installation. Is it the same for you ? In that case, they are exactly 
equivalent for QGis. When QGis finds a dataset without a clear CRS code, 
it will parse the proj4 string to find the coordinate system and stop at 
the first corresponding one.

Regards,

Leyan

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