[PROJ] EPSG:3034 axis ordering

[Even Rouault]

On mardi 30 avril 2019 15:17:30 CEST Erik Ravhed wrote:
> Hi all,
> 
> I have a question regarding EPSG:3034 and its axis ordering. According
> to https://www.epsg-registry.org the order of the axes should be ordered
> as northing easting. Looking at the proj4 definition it is defined as
> the following:
> 
> +proj=lcc +lat_1=35 +lat_2=65 +lat_0=52 +lon_0=10 +x_0=4000000 +y_0=2800000
> +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
> 
> Looking at this definition I don't see how I can determine that
> EPSG:3034 should be treated as a northing easting. Shouldn't |+axis=neu|
> be a part of the proj4 definition?
> 

Presumably, but proj strings will remain like that forever at that point of 
history, since axis order of projectedCRS was never a concern in PROJ < 6 era, 
and a lot of users of those code still wanted easting, northing order whatever 
EPSG said.

PROJ 6 is now fully axis aware, so when doing a transformation from ETRS89 
lat/long to EPSG:3034, you get:

$ src/projinfo -s EPSG:4258 -t EPSG:3034 -o PROJ

PROJ string:
+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert 
+xy_in=deg +xy_out=rad +step +proj=lcc +lat_0=52 +lon_0=10 +lat_1=35 +lat_2=65 
+x_0=4000000 +y_0=2800000 +ellps=GRS80 +step +proj=axisswap +order=2,1

So you have a first axisswap operation to go from input lat,long to internal 
long,lat, then the map projection, and then another axisswap operation to go 
from te internal easting,northing to final northing,easting

Even


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