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

[Roman Luštrik]

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>
> ​
>
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>
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-- 
In God we trust, all others bring data.

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