[R-sig-Geo] Setting FID values when saving GML files with writeOGR
Roger.Bivand at nhh.no
Fri Aug 26 20:36:03 CEST 2011
On Fri, 26 Aug 2011, Roger Bivand wrote:
> 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!
Indeed, the driver internals are a possible solution, see:
which suggests that some reading is possible in OGR >= 1.8.0, but that
writing will first come with OGR >= 1.9.0, that is the development
version, I believe. If this really matters for you, please look carefully
at commits on the GDAL trunk in the GML driver. I think that there have
been recent developments, with increased speed claimed. Consequently,
there isn't much that can be done from the R side, you'll need an rgdal
built against a future version of GDAL/OGR.
> Best wishes,
>> Karl Ove Hufthammer
>> R-sig-Geo mailing list
>> R-sig-Geo at r-project.org
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
More information about the R-sig-Geo