[Qgis-user] Re: Export to ETRS-35TM-FIN (EPSG 3067) fails

[Jukka Rahkonen]

Giuseppe Sucameli <sucameli at ...> writes:

> 
> Hi Timo,
> 
> On Tue, Aug 30, 2011 at 1:13 PM, Timo Metsänen
> <timo.metsanen at ...> wrote:
> > export coordinates (have tried from KKJ / Finland Uniform Coordinate
> System EPSG:2393 and WGS 84 EPSG:4326) to ETRS-35TM-FIN (EPSG
> > 3067), shapefile gets value "EPSG:3047 - ETRS89 / ETRS-TM35".
> > Does anyone have explanation to this or even better, solution?
> 
> Looking at those CRSs, both them have the same proj4 string definition:
> +proj=utm +zone=35 +ellps=GRS80 +units=m +no_defs
> 
> For this reason you get EPSG:3067 instead of EPSG:3047.

This is a very bad thing actually because axis order in EPSG:3067 is
Easting-Northing but EPSG:3067 is using Northing easting. This difference will
make you mad with WMS 1.3.0, WFS 1.1.0, GML 3 and so on. Compare 
http://epsg-registry.org/report.htm?type=selection&entity=urn:ogc:def:crs:EPSG::3047&reportDetail=short&style=urn:uuid:report-style:default-with-urn&style_name=OGP%20Default%20With%20Urn&title=EPSG:3047
with 
http://epsg-registry.org/report.htm?type=selection&entity=urn:ogc:def:crs:EPSG::3067&reportDetail=short&style=urn:uuid:report-style:default-with-urn&style_name=OGP%20Default%20With%20Urn&title=EPSG:3067

There is probably another issue which will give you 100-200 meter transformation
errot because Proj4 tends to lack the +towgs84 parametert for the Finnish KKJ
zones (EPSG:2391-EPSG:2394). All programs using Proj4 make this same error (GDAL
when using the EPSG codes for giving the projection, Mapserver, PostGIS,
Spatialite etc.) It may be that the very latest Proj4 comes with correct
+towgs84 parameters but it does not help with old program versions.

The only really reliable way for doing the conversion is to use ogr2ogr from
command line. Read the instructions from
http://latuviitta.org/documents/YKJ-TM35FIN_muunnos_ogr2ogr_cs2cs.txt (in
Finnish). You can use other tools as well but compare always the result with
something you know to be correct. And if some program works now, after program
update the transformation can be wrong again. Do not ever trust that conversion
between KKJ and other systems goes right. Best thing to do is to make conversion
right once and after that stop using KKJ at all.



-Jukka Rahkonen-