[R-sig-Geo] rgeos::gBuffer(, byid=TRUE) fails

[Josh O'Brien]

On Tue, Feb 9, 2016 at 5:01 AM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
> On Mon, 8 Feb 2016, Roger Bivand wrote:
>
>> On Mon, 8 Feb 2016, Josh O'Brien wrote:
>>
>>>  Oops. The post's title should have read "rgeos::gBuffer( , byid=TRUE)
>>>  fails when...". (I inadvertently left out the `byid=TRUE` bit).
>>>
>>>  My apologies.
>>>
>>>  On Mon, Feb 8, 2016 at 9:59 AM, Josh O'Brien <joshmobrien at gmail.com>
>>>  wrote:
>>> >  Hello,
>>> > >  Not sure if this would be considered a bug, but it did recently bite
>>> >  me (and might bite others using gBuffer(..., byid=TRUE)
>>> >  programatically).
>>> >
>>
>>
>> Thanks for a reproducible example - for rgeos 0.3-14 this gives a
>> segfault, in 0.3-16 an error as the data.frame has only one row, but three
>> Polygons objects are returned. As you note, the issue is triggered by
>> byid=TRUE but there is only one input object; only one buffer is created,
>> around the NE island.
>>
>> I'll look into this - it'll need debugging in C, close to recent bug-fixes
>> (then concerned with pre-sp-MultiPoint object signalling - multiple objects
>> making up features).
>
>
> I have committed a fix to R-Forge (checking whether the length of spgeom ==
> 1 and byid == TRUE, if so set byid=FALSE and warn). The problem was visible
> in the C code, but there we don't have an sp-class generic "length" measure
> of the # features, so the modification is at the R level.
>
> Which OS would you like to test under?
>

I'm using it on Windows (with R-3.2.3) and Ubuntu 14.04 (with
R-3.2.2), but am afraid I don't know how to install from sources on
either. I'll test under both, but if I had to pick one, would go with
Ubuntu, since that's where I'm doing my production work.

Thanks so much,

- Josh


> Best wishes,
>
> Roger
>
>
>>
>> And yes, this is a reasonable place to report, it should give users a
>> realistic view of how many corner cases actually exist and require someone's
>> attention.
>>
>> Roger
>>
>>> > >      library(sp)
>>> >      library(rgdal)
>>> >      library(rgeos)
>>> > >      ## Example SpatialPolygonsDataFrame
>>> >      x <- readOGR(system.file("etc/shapes", package="spdep"), >
>>> > "sids")[c(89,28),]
>>> >      plot(x, col=c('dodgerblue', 'wheat'))
>>> > >      ## Works fine on object with multiple @Polygons in @polygons,
>>> > > even
>>> >      ## if one of the @Polygons is multi-part
>>> >      gBuffer(x, width=0.01, byid=TRUE)
>>> > >      ## Works with a single single-part @Polygons object in @polygons
>>> >      gBuffer(x[1,], width=0.01, byid=TRUE)
>>> > >      ## Fails with a single _multi-part_ @Polygons object in
>>> > > @polygons
>>> >      gBuffer(x[2,], width=0.01, byid=TRUE)
>>> > > >  Thanks (and please let me know an rgeos-specific note like this
>>> > > > would
>>> >  be better posted elsewhere),
>>> > >  Josh O'Brien
>>>
>>>  _______________________________________________
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>>>  R-sig-Geo at r-project.org
>>>  https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>
>>
>>
>
> --
> Roger Bivand
> Department of Economics, Norwegian School of Economics,
> Helleveien 30, N-5045 Bergen, Norway.
> voice: +47 55 95 93 55; fax +47 55 95 91 00
> e-mail: Roger.Bivand at nhh.no
> http://orcid.org/0000-0003-2392-6140
> https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
> http://depsy.org/person/434412