[R-sig-Geo] Setting FID values when saving GML files with writeOGR
Roger.Bivand at nhh.no
Fri Aug 26 19:45:34 CEST 2011
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!
> Karl Ove Hufthammer
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
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e-mail: Roger.Bivand at nhh.no
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