[PROJ] Coordinates in Lat/Lon or Lon/Lat

[Javier Jimenez Shaw]

Hi Alain

EPSG:4326 is expecting lat-long. So the proper way is
echo "70 10 0" | cs2cs EPSG:4326 EPSG:5041

The axis swap is because internally all the projections are expecting
easing-northing coordinates, so they should be swapped from the
northing-easing that is the input.

An easy way to see the axis order is looking at the WKT2 representation of
a CRS.

On Fri, 14 Apr 2023 at 08:29, Alain Orsoni <Alain.Orsoni at ign.fr> wrote:

> Hello,
>
> Basic question but necessary for me :
>
> We use PROJ Version 8.2.1
> Exemple : I convert from Longitude=10 Latitude=70 from 4326 to UPS stereo
> North Pole (5041)
>
> projinfo -s EPSG:4326 -t EPSG:5041 -o PROJ
> Gives output :
>
> +proj=pipeline
>   +step +proj=axisswap +order=2,1
>   +step +proj=unitconvert +xy_in=deg +xy_out=rad
>   +step +proj=stere +lat_0=90 +lon_0=0 +k=0.994 +x_0=2000000 +y_0=2000000
>         +ellps=WGS84
>
> But
> echo "10 70 0" | cs2cs EPSG:4326 EPSG:5041
>
> Gives output : 11976062.58 -1630989.83 0.00
> The good result given by EPSG.IO is  : 2389386.90 -208322.83 0.00
> I get the good result with : echo « 70 10 0" | cs2cs EPSG:4326 EPSG:5041
>
> So it seems that the syntax. cs2cs EPSG:4326 EPSG:5041  doesn’t apply the
> step axisswap
>
> Can someone confirm this behavior ?
>
> Second question :
> In C++ API the proj_create_crs_to_crs() associated to
>  proj_normalize_for_visualization() allows to avoid this problem.
> But we use also PROJ in shell scripts. It seems to me that some
> geodetic_crs expect lat-lon entry and some other Lon-lat.
> Is there a way in the SQL database (proj.db) to find this information?
>
> Thanks for any answer.
>
> Alain
>
>
>
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