[R-sig-Geo] gBuffer solution to invalid objects problem fails

[Roger Bivand]

There is an example in the message, but Kenny is ignoring the message from 
gBuffer:

Warning message:
In gBuffer(new_poly, width = 0) :
   Spatial object is not projected; GEOS expects planar coordinates

and the differences in geographical coordinates are small. The warning is 
given for a reason. Intersection is projection-agnostic, but buffer is 
not. I don't know whether this is the reason.

Roger


On Thu, 19 May 2016, Roman Luštrik wrote:

> Hi Kenny,
>
> can you provide a small, reproducible example which replicates this
> behavior?
>
> Cheers,
> Roman
>
> On Wed, May 18, 2016 at 7:08 PM, Kenny Bell <kmb56 at berkeley.edu> wrote:
>
>> Hi all,
>>
>> I have been getting the below error a few times. I have seen in several
>> places that a zero-width gBuffer call will fix the topology problem.
>> However, in this case, I find that the call to gBuffer generates a 4 point
>> horizontal line, not solving the problem. Is there another solution? Thanks
>> for any help!
>>
>> My code:
>>
>> library(sp)
>> library(rgeos)
>> load("r-sig-geo.RData")
>>
>> gIntersection(grid_poly, new_poly,
>>               byid = c(TRUE, FALSE),
>>               id = as.character(grid_poly at data[,1]),
>>               # if there are coinciding lines, gIntersection
>>               # returns a cross.
>>               drop_lower_td = TRUE,
>>               checkValidity = TRUE)
>> # new_poly is invalid
>> # Error in rgeos::gIntersection(grid_poly, new_poly, byid = c(TRUE, FALSE),
>>  :
>> #                                 Invalid objects found
>> #                               In addition: Warning message:
>> #                                 In RGEOSUnaryPredFunc(spgeom, byid,
>> "rgeos_isvalid") :
>> #                                 Self-intersection at or near point
>> 172.23206269997971 -42.13157792003453
>>
>> # Try using gBuffer as suggested here:
>> #
>>
>> http://gis.stackexchange.com/questions/163445/r-solution-for-topologyexception-input-geom-1-is-invalid-self-intersection-er
>>
>> new_poly1 <- gBuffer(new_poly, width = 0)
>> plot(new_poly1)
>> # Generates a line (i.e. kills the polygon)​
>> ​
>>   r-sig-geo.RData
>> <https://www.dropbox.com/s/9ivpcmboodpu6zd/r-sig-geo.RData?dl=0>
>> ​
>>
>>         [[alternative HTML version deleted]]
>>
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo at r-project.org
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
>
>
>
> -- 
> In God we trust, all others bring data.
>
> 	[[alternative HTML version deleted]]
>
> _______________________________________________
> 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