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

[Roger Bivand]

On Tue, 9 Feb 2016, Josh O'Brien wrote:

> 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.

After some exchanges off-list, rgeos 0.3-17 has now reached CRAN with 
modifications handling the problem. Once again, the key was the simple, 
reproducible example.

Thanks to Josh for his help,

Roger

>
> 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
>>>>
>>>>  _______________________________________________
>>>>  R-sig-Geo mailing list
>>>>  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
>

-- 
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