[R-sig-Geo] Setting FID values when saving GML files with writeOGR

[Roger Bivand]

On Thu, 25 Aug 2011, Karl Ove Hufthammer wrote:

> Dear list members,
>
> Is it possible to define which FID values should be used when 
> saving a SpatialPointsDataFrame to a GML files using writeOGR 
> (rgdal package)?
>
> The FID values are stored as <ogr:layername fid="F0"> (and F1, 
> F2, …). If I insert a new row in the SPDF, most features change 
> their FID, which creates much unneccessary noise in our VCS,
> so I would like to use an already existing ID as the FID.
>
> I have tried change both the row.names and adding columns named
> ‘fid’ and ‘gml_id’, the writeOGR still only uses F0, F1, … as 
> the FIDs.

No FID is set in writeOGR() in the underlying C++ function writeOGR(). One 
could be set, but only as unique integers >= 0, not as the row.names() 
which are strings. The result is that default FID are written. It would be 
possible to modify the function to add integer FID, I think, but they 
would have to be valid unique integers. I think that what gets 
written from there depends on the driver internals, which the 
function does not reach. Would this help? Patches welcome!

Best wishes,

Roger

>
> -- 
> Karl Ove Hufthammer
>
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-- 
Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no