[gdal-dev] Reprojection shapefile using ogr2ogr from EPSG:28992 to EPSG:4326

[Even Rouault]

Pierric,

> In my case shapefile are uploaded to the server by users through a web page
> (polygons represent the boundaries of a new protected natural site). So the
> only information about the projection that I get is located in the .prj
> file. I am not sure if there is a way to get the EPSG code automatically in
> this case (?)

Not yet currently. Althgouth this is a much desired feature that waits from 
contributions/funding.

> 
> How can QGIS pick up the name of the EPSG code right (actually I knew that
> the projection code was EPSG:28992 by opening the shapefile in QGIS and
> checking the properties of the layer)   ?

It has some heuristics where it tries to match the proj.4 string deduced from 
the .prj file with the ones of the EPSG database. But that's not a full proof 
mecanism. There can be be misattributions because some SRS have very close 
definitions that come to identical proj.4 strings.

> 
> In the case there is no way to get the EPSG code automatically: do you know
> if ogr2ogr could send a warning/error that I would send back to the user
> asking him to reproject the shapefile in WGS84 himself before uploading the
> file?

There's no way ogr2ogr could guess there's information missing. It can makes 
sense of the .prj as it is currently. It is just that there's a missing piece 
of information in it that must be retrieved by other means, while above 
heuristics is not implemented.

Even

> 
> Thanks in advance for your insights
> 
> 2015-01-22 19:54 GMT+01:00 Even Rouault <even.rouault at spatialys.com>:
> > Le jeudi 22 janvier 2015 19:43:50, Pierric de Laborie a écrit :
> > > Hello,
> > > 
> > > I do not understand why there seems to be a drift (about 100 meters) of
> > 
> > the
> > 
> > > polygons contained in a shapefile after reprojecting it to 4326 using
> > > the following command :
> > > 
> > > ogr2ogr -f 'ESRI Shapefile' -wrapdateline -t_srs EPSG:4326
> > > destinationfile.shp sourcefile.shp
> > > 
> > > The original prj file is the following. It is supposed to describe the
> > > projection EPSG:28992  ( http://spatialreference.org/ref/epsg/28992/  )
> > > 
> > > PROJCS["RD_New",GEOGCS["GCS_Amersfoort",DATUM["D_Amersfoort",
> > > SPHEROID["Bessel_1841",6377397.155,299.1528128]],
> > > PRIMEM["Greenwich",0.0],
> > > UNIT["Degree",0.0174532925199433]],
> > > PROJECTION["Double_Stereographic"],
> > > PARAMETER["False_Easting",155000.0],
> > > PARAMETER["False_Northing",463000.0],
> > > PARAMETER["Central_Meridian",5.38763888888889],
> > > PARAMETER["Scale_Factor",0.9999079],
> > > PARAMETER["Latitude_Of_Origin",52.15616055555555],
> > > UNIT["Meter",1.0]]
> > 
> > This definition is outdated and has not the needed datum shift :
> > 
> > $ gdalsrsinfo EPSG:28992
> > 
> > PROJ.4 : '+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889
> > +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel
> > +towgs84=565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725
> > +units=m +no_defs '
> > 
> > OGC WKT :
> > PROJCS["Amersfoort / RD New",
> > 
> >     GEOGCS["Amersfoort",
> >     
> >         DATUM["Amersfoort",
> >         
> >             SPHEROID["Bessel 1841",6377397.155,299.1528128,
> >             
> >                 AUTHORITY["EPSG","7004"]],
> > 
> > TOWGS84[565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725],
> > 
> >             AUTHORITY["EPSG","6289"]],
> >         
> >         PRIMEM["Greenwich",0,
> >         
> >             AUTHORITY["EPSG","8901"]],
> >         
> >         UNIT["degree",0.0174532925199433,
> >         
> >             AUTHORITY["EPSG","9122"]],
> >         
> >         AUTHORITY["EPSG","4289"]],
> >     
> >     PROJECTION["Oblique_Stereographic"],
> >     PARAMETER["latitude_of_origin",52.15616055555555],
> >     PARAMETER["central_meridian",5.38763888888889],
> >     PARAMETER["scale_factor",0.9999079],
> >     PARAMETER["false_easting",155000],
> >     PARAMETER["false_northing",463000],
> >     UNIT["metre",1,
> >     
> >         AUTHORITY["EPSG","9001"]],
> >     
> >     AXIS["X",EAST],
> >     AXIS["Y",NORTH],
> >     AUTHORITY["EPSG","28992"]]
> > > 
> > > Apparently QGIS could understand the projection file correctly and
> > > reproject it to WGS84 with no problem. But it seems that for some
> > 
> > specific
> > 
> > > projections, GDAL does not reproject as expected.
> > 
> > Shapefile .prj files don't include TOWGS84, so that's the likely
> > explanation.
> > Try adding -s_srs  EPSG:28992 to your ogr2ogr command line
> > 
> > >  Is it possible to force it by adding the projection specifications in
> > 
> > one
> > 
> > > of the files included in the following folder (linux debian install) :
> > >  /usr/share/gdal   and how ?
> > > 
> > > For example, I could see a file named gdal_datum.csv  containing the
> > 
> > datum
> > 
> > > "D_Amersfoort" specified in the prj file. However I could not find in
> > > any other files the projection GCS_Amersfoort or RD_New as specified
> > > in the
> > 
> > prj
> > 
> > > file.
> > > 
> > > Thanks for your help
> > 
> > --
> > Spatialys - Geospatial professional services
> > http://www.spatialys.com

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