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Sorry for asking this basic question, but I couldn't get the solution from the previous answers.

I need to extract the Lat/long coordinates of the centroids of districts. My QGIS project SCR and the different layers have all been set on "WGS 84 / UTM zone 18N".

I've created the centroids using the usual tool. I could then extracted the coordinates using the "Vector > Geometry Tools > Export/Add Geometry Columns", or saving the layer in CSV typing "GEOMETRY=AS_XY" in the "Layers" part of the "OGR creation options".

Nevertheless, both methods output Cartesian coordinates, whereas I need Lat/long coordinates.

How can I do?

Thanks for your help.

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3 Answers 3

You have to reproject the point layer to EPSG:4326 first. Right-click on the layer name in layer list and select "Save as ...". There, you can specify the target CRS to be EPSG:4326.

Load the new reprojected point layer and then run "Export/Add Geometry Columns".

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Thanks a lot. It worked perfectly. –  Stanislas Rebaudet Mar 30 '12 at 13:59
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Note that with newer version of QGIS (accessible via OSGeo4W installer) you don't even need to Export a layer to a new CRS. You only need to change CRS of the map canvas to whatever is you choice for output units and CRS and check "Calculate using Project CRS" when doing "Export/Add Geometry Columns" and output to the same shapefile. –  Maxim Dubinin Mar 31 '12 at 14:40
    
@StanislasRebaudet Please accept the answer if your problem is solved. –  underdark Mar 31 '12 at 15:53
    
Hello! What new fields are added to the output table when using Export/Add Geometry Columns? When I follow the instructions above, my output table contains two new fields "Area" and "Perimeter". These two fields do not contain Lat/Long values. Huh? I was expecting that the new fields would be something like "Lat" and "Long", or "X" and "Y". QGIS 1.8, Windows 7. –  Stu Smith Nov 23 '12 at 21:45
    
If you get "area" and "parameter" you must have used a polygon layer, right? I thought you had a point layer ... –  underdark Nov 23 '12 at 21:58
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One option could be specifying the layer CRS as WGS 84(no projection). May be you will have to change the project CRS too. Now use "Vector > Geometry Tools > Export/Add Geometry Columns". This should give you Lat/long coordinates.

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Extract nodes. This makes it into a point layer. Then open attribute table, field calculate, Geometry-$y/$x

find polygon corner coordinates

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