[R-sig-Geo] Possible rgdal enhancement request related to null attributes

[- -]

Roger,

It appears you preserved the pre 2.2 behavior which is what I think most people would expect, keep the attribute and set it as Null. 

That is not the case with other OGR related tools. I just hadn't had a chance to verify it in R, and had the issue come up in QGIS, so I appreciate you pointing out where in the code you addressed it (I did try to read through that file and didn't find that on my own).

The only reason I could see people wanting to drop nulls, is that certain formats would be more efficient. In the case of GeoJson it could result in a significantly smaller file. Though personally I think that a separate minification tool would be a better place to make that change. Which would mean a user would only need an override option if you had gone with UnsetField as the default.

So at this time I don't see any additional changes needed.

Thanks,
Alex
> On July 10, 2017 at 9:04 AM Roger Bivand <Roger.Bivand at nhh.no> wrote:
> 
> 
> Hi Alex,
> 
> GDAL 2.2 is supported in rgdal and in sf - has been for some time. If GDAL 
> >= 2.2:
> 
> https://r-forge.r-project.org/scm/viewvc.php/pkg/src/OGR_write.cpp?root=rgdal&r1=650&r2=660
> 
> and
> 
> https://r-forge.r-project.org/scm/viewvc.php/pkg/src/ogrsource.cpp?root=rgdal&r1=650&r2=660
> 
> This is general, not just GeoJSON, see
> 
> https://trac.osgeo.org/gdal/wiki/rfc67_nullfieldvalues
> 
> I don't see a good reason for making the user have to choose - could you 
> suggest one with a use case reprex?
> 
> See also the sf code, which is relevant here.
> 
> Roger
> 
> On Fri, 7 Jul 2017, Alex M wrote:
> 
> > Roger et al,
> >
> > I couldn't find a ticket system for rgdal so this seemed the best place
> > to post.
> >
> > We just hit a bug (in QGIS [1]) of sorts due to a change in behavior in
> > GDAL from 2.1.x to 2.2.x in the way null fields are handled. [2]
> >
> > Short story if you have a column of null values and you save a geojson
> > those fields are not saved. So the next time you open up the file, you
> > have less columns than before. It's great for minifying geojson but
> > terrible for many other use cases.
> >
> > I'm not 100% sure this will show up in rgdal (2.2 hasn't been pushed to
> > my Ubuntu yet so I haven't tested), but there's a good chance it will
> > depending on how R deals with unset vs null. If someone would like to
> > test, you can get a sample file from [3], readOGR and then writeOGR (to
> > geojson) and see if the null columns vanish.
> >
> > The enhancement requested to deal with this, is to provide the user an
> > option that allows them to decide when a field is unset vs null. Or
> > maybe just a clarification on how R represents that data and how a user
> > could set a field as null instead of unset and vice versa.
> >
> > Even R. pointed out that this can be controlled with the
> > OGR_F_IsFieldNull() part of the ogr api.
> >
> > [1] https://issues.qgis.org/issues/16812
> > [2] https://trac.osgeo.org/gdal/wiki/rfc67_nullfieldvalues
> > [3] https://github.com/UCDavisLibrary/ava/issues/270
> >
> > Thanks,
> > Alex
> >
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> >
> 
> -- 
> Roger Bivand
> Department of Economics, Norwegian School of Economics,
> Helleveien 30, N-5045 Bergen, Norway.
> voice: +47 55 95 93 55; e-mail: Roger.Bivand at nhh.no
> Editor-in-Chief of The R Journal, https://journal.r-project.org/index.html
> http://orcid.org/0000-0003-2392-6140
> https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
> 
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