[R-sig-Geo] Delimit a polygon for the region which is>, 1000 m from my raster altitude

[sadaoui]

Thank you very much  "José M. Blanco Moreno" 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 polygon

library(rgeos)
pol2 <- rasterToPolygons(r, fun=function(x){x>500}, dissolve = TRUE) 
pol3 <- gBuffer(pol2,width=0, byid=FALSE) 
plot(r)

plot(pol3,add=TRUE,border='blue',lwd=2,col="red",axes=TRUE) 
title("area > 500m")


I have had the result as I want a polygon for the area> 500m.

But, 
I found a problem to export this polygon (pol3)

#export polygon to shapefile

library(rgdal)
writeOGR(pol3, ".", "polygon3", driver="ESRI Shapefile")

Error in writeOGR(pol3, ".", "polygon3", driver = "ESRI Shapefile") : 
  obj must be a SpatialPointsDataFrame, SpatialLinesDataFrame or
    SpatialPolygonsDataFrame

it has not recognized as a polygon!!! I don't know why?

thank you for helping me to the last key






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