[PROJ] EPSG:3034 axis ordering

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[PROJ] EPSG:3034 axis ordering

Erik Ravhed
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?

Best Regards,
Erik

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Re: EPSG:3034 axis ordering

Even Rouault-2
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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Re: EPSG:3034 axis ordering

Erik Ravhed
Thanks for the quick reply and explanation!

Erik

On 4/30/19 3:54 PM, Even Rouault wrote:

> 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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