[Qgis-user] What's wrong with PRJ file for CRS 3857?

[Goyo]

To replicate this:

Load the attached shapefile in QGIS. It is displayed as EPSG:3857.
Delete or rename test.cpg and load the layer again. This time it is
displayed as EPSG:54004. The displayed positions are shifted.

According to my understanding the difference between 3857 and 54004 is
that the former projects elipsoidal coordinates as if they were
spherical coordinates (so the whole earth is projected into a perfect
square). But the corresponding .prj files do not reflect this. Perhaps
this is be due to limitations in the format required for .prj files?

Regards

Goyo


2015-09-16 15:43 GMT+02:00 Redoute <redoute at tortenboxer.de>:
> Am 16.09.2015 um 12:15 schrieb Bernhard Ströbl:
>
>> hope this helps
>
> It seems my question was not very clear, so in other words (all "as far
> as I understand"):
>
> When I create a shapefile with CRS 3857 (Pseudo Mercator), and upload it
> to the cartodb web service, the features are shifted. I tried to inspect
> this and could reproduce the same behaviour in QGIS itself:
>
> QGIS creates two files for projection with two forms of WKT, which
> should express the same projection:
>
> .prj:
> PROJCS["WGS_84_Pseudo_Mercator",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Mercator"],PARAMETER["central_meridian",0],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1],PARAMETER["standard_parallel_1",0.0]]
>
> .qpj:
> PROJCS["WGS 84 / Pseudo-Mercator",GEOGCS["WGS
> 84",DATUM["WGS_1984",SPHEROID["WGS
> 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]],PROJECTION["Mercator_1SP"],PARAMETER["central_meridian",0],PARAMETER["scale_factor",1],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["X",EAST],AXIS["Y",NORTH],EXTENSION["PROJ4","+proj=merc
> +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0
> +units=m +nadgrids=@null +wktext +no_defs"],AUTHORITY["EPSG","3857"]]
>
> To reproduce the problem with cartodb, I deleted the qpj file (as other
> applications are expected to ignore this suffix) and loaded the
> shapefile into QGIS. The layer properties then show EPSG 54004 World
> Mercator and I see the same shift as in cartodb. The coordinate
> 774575/6610921, which marks Cologne Cathedral in 3857, is projected into
> a lake near Duesseldorf.
>
> So I think there is something wrong either with the shorter WKT, or how
> it is interpreted by QGIS or GDAL/OGR. Once you know this, a workaround
> is obvious. I hope with your help we can describe the error more
> precisely to make an informed bug report.
>
> Am 16.09.2015 um 12:15 schrieb Bernhard Ströbl:
>> Hi,
>>
>> general: read the documentation on projections, be sure to know what
>> projections are and what they are used for.
>>
>> specific: both your project and your data have a projection (spatial
>> reference system). Cases:
>> 1) both match => you're ok
>> 2) both differ => QGIS can reproject the data on-the-fly => you're ok
>> 3) the projection assigned to the data is wrong (I assume this is your
>> case but without more info on what you do nobody can tell). Tell QGIS in
>> layer properties which projection your data is in (the prj and qpj files
>> do just that), then goto either case 1 or case 2
>>
>> hope this helps
>>
>> Bernhard
>>
>> Am 16.09.2015 um 11:46 schrieb Redoute:
>>> This question is arising from
>>> http://gis.stackexchange.com/questions/162779/why-is-the-city-of-san-francsico-floating-over-point-richmond
>>>
>>> I create a shapefile in QGIS in CRS 3857. I delete the .qpj file and
>>> load the shapefile again. The features then are placed wrong, the
>>> Cologne Cathedral shows up in a lake near Duesseldorf :-((. So I reason
>>> there is something wrong with the .prj file.
>>>
>>> What is it? Is it a bug in GDAL/OGR?
>>> Tested with QGIS 2.10.1.
>
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