Delimit a polygon for the region which is>, 1000 m from my raster altitude

You can try fiddling a bit with:

pol2 <- rasterToPolygons(r, fun=function(x){x>6}, dissolve = TRUE)

pol3 <- gBuffer(pol2,width=1e-5, byid=FALSE)

Where the width is sufficiently small as to not affect the general shape. However, it yields very jagged polygons, which I do not know if it is what you intend.

Best wishes,

Jos? M. Blanco

El 02/05/2015 a las 12:00, r-sig-geo-request at r-project.org<mailto:r-sig-geo-request at r-project.org> escribi?:

Subject: Re: [R-sig-Geo] Delimit a polygon for the region which is>
        1000 m from my raster altitude
Message-ID: <1430485336885-7588149.post at n2.nabble.com><mailto:1430485336885-7588149.post at n2.nabble.com>
Content-Type: text/plain; charset=us-ascii

Thank you very much "MacQueen, Don"  for your answer.

I have followed your instructions from this script :

library(raster)
library(sp)

f <- system.file("external/test.grd", package="raster")
r <- raster(f)

# add contour

x <- rasterToContour(r,levels=500)
class(x)
plot(r)
plot(x, add=TRUE)

#export contour to shapefile

library(rgdal)

writeOGR(x, ".", "contour", driver="ESRI Shapefile")

but when I open the shapefile, is a  lines not a polygons? My goal is to
have the polygon areas for altitude> 500m.

I thought to "rasterToPolygons"

library(raster)
library(sp)
f <- system.file("external/test.grd", package="raster")
r <- raster(f)

# add polygon

library(rgeos)

pol <- rasterToPolygons(r, fun=function(x){x>500})

plot(pol, add=T, col='red')

#export polygon to shapefile

library(rgdal)

writeOGR(pol, ".", "polygon", driver="ESRI Shapefile")

but the result, it displays a shapefile with polygons for each pixel

I just want  a polygons to areas where are> 500m, not for each pixel.

Thank you again

--
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Jos? M. Blanco-Moreno
Dept. de Biologia Vegetal (Bot?nica)
Facultat de Biologia
Universitat de Barcelona
Av. Diagonal 643
08028 Barcelona
SPAIN
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