[R-sig-Geo] Polygon edge smoothing

[Pierre Roudier]

Hi Sébastien,

Maybe you should have a look to the rgeos package. It offers bindings
for the GEOS C++ lib. Note that unlike the gpclib, it is really
open-source (beware of the gpclib licence terms - they are very
restricted). However, it is not (AFAIK) on CRAN yet. You have to
install it from r-forge:

install.packages("rgeos", repos="http://R-Forge.R-project.org")

The function you want is probably gSimplify(). I never used that
functionality so I unfortunately can't help you more on that!

HTH,

Pierre

2010/12/6 Sébastien Durand <v8extra at gmail.com>:
> Here is what I found as a temporary solution:
>
> Here is my example:
>
>
> library(akima)
> library(maptools)
> library(zoo)
> gpclibPermit()
> library(raster)
> data(akima)
>
> # define de dimension of grid
> dimgrid <- 50
>
> # Interpolate to regular grid
> ak.li <- interp(akima$x, akima$y, akima$z, xo=seq(min(akima$x),
> max(akima$x), length = dimgrid),yo=seq(min(akima$y), max(akima$y),
> length = dimgrid),linear = TRUE, extrap=FALSE, duplicate = "mean")
>
> # Show interpolation
> image(ak.li)
> points(akima)
> with(akima, text(x, y, formatC(z,dig=2), adj = -0.1))
>
> r <- raster(ak.li)
> plot(r)
>
> pol <- rasterToPolygons(r, fun=function(x){x>20 & x<25})
>
> # Show the polygons
> plot(pol, add=T, col='red')
>
> ### new code
> digits <- 6
> for (i in 1:length(pol at polygons)) {
>        for (j in 1:length(pol at polygons[[i]]@Polygons)) {
>                        pol at polygons[[i]]@Polygons[[j]]@coords <-
>                        round(pol at polygons[[i]]@Polygons[[j]]@coords, digits)
>        }
> }
>
>
> # Attempt to merge similar adjacent into one polygon
> union = unionSpatialPolygons(pol, ID=rep(1, times=length(pol at polygons)))
>
> # Show
> plot(union, add=TRUE, col="white")
>
> # Nombre de vertices
> crds=union at polygons[[1]]@Polygons[[1]]@coords
> tmp=length(crds[,1])
>
> nexCoordX= rollmean(c(crds[tmp,1], crds[,1], crds[1,1]), k=2)
> nexCoordY= rollmean(c(crds[tmp,2], crds[,2], crds[1,2]), k=2)
> lines(nexCoordX, nexCoordY, col="yellow", lwd=2)
>
>
> If you have any knowledge of a function that would do something similar, I would be happy to ear about it!
>
> Thanks a lot!
>
> Sébastien
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