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 <joshmobr...@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?
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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--
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.biv...@nhh.no
http://orcid.org/0000-0003-2392-6140
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http://depsy.org/person/434412
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