[gdal-dev] myshape.prj versus -s_srs

[Frank Warmerdam]

Stefan Keller wrote:
> I'm trying to a shapefile to KML. The Shapefile driver indicates that 
> "If a .prj files (...) is present, it will be read and used to associate 
> a projection with features.". In addition, the OGR KML driver 
> documentation says "All OGR KML output will be presented in EPSG:4326.".
>  
> Let's say the input files are myshape.shp, myshape.shx, myshape.dbf and 
> myshape.prj and I try "ogr2ogr -f kml out.kml myshape.shp".
> then the resulting coordinates are still in the source coordinate 
> system: Why? I espected that theya re transformed to WGS84 according to 
> the documentation mentioned.
>  
> This is what finally worked: "ogr2ogr -f kml del_prairie.kml 
> del_prairie.shp -s_srs EPSG:21781 -t_srs EPSG:4326". But indicating 
> "-s_srs EPSG:21781" seems to me redundant to the existing file 
> myshape.prj . Any explanations?

Stefan,

ogr2ogr does not reproject coordinates by default, even when writing
to formats like KML that only really support one output coordinate system
properly.  The -t_srs is the correct way to request reprojection.

The -s_srs EPSG:21781 option should be unnecessary if the source shapefile
already has a readable .prj file.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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