Many thanks Roger. I thought proj4string(spAll) <- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84") took care of projection, but obviously not. How do I project?
Ross On 29 Mar 2013, at 12:54, Roger Bivand <roger.biv...@nhh.no> wrote: > On Fri, 29 Mar 2013, Ross Ahmed wrote: > >> Hi all, >> >> I have this list of polygons: >> >> library(sp) >> p1 <- Polygon(cbind(c(-1.672487,-1.663689,-1.663185,-1.672258,-1.672487), >> c(55.58951,55.58948,55.58249,55.58260,55.58951))) >> p2 <- Polygon(cbind(c(-1.663689, -1.655508, -1.65514, -1.6633, -1.663689), >> c(55.589485, 55.589554, 55.582396, 55.582428, >> 55.589485))) >> p3 <- Polygon(cbind(c(-1.672224, -1.663046, -1.662525, -1.672137, >> -1.672224), >> c(55.582142, 55.582044, 55.575139, 55.575348, >> 55.582142))) >> >> sp1 <- Polygons(list(Polygon(p1)),"p1") >> sp2 <- Polygons(list(Polygon(p2)),"p2") >> sp3 <- Polygons(list(Polygon(p3)),"p3") >> spAll <- SpatialPolygons(list(sp1, sp2, sp3)) >> proj4string(spAll) <- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84") >> >> >> ?.and also this single polygon: >> >> poly1 <- Polygon(cbind(c(-1.666566, -1.659071, -1.658532, -1.666459, >> -1.666566), >> c(55.586296, 55.586357, 55.580414, 55.580505, >> 55.586296))) >> spoly1 <- Polygons(list(Polygon(poly1)),"poly1") >> spoly1 <- SpatialPolygons(list(spoly1)) >> proj4string(spoly1) <- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84") >> >> >> I need to find the proportion of ?spoly1? that is overlapped by ?sp1?, >> ?sp2?, ?sp3? and no polygon. The output should be something like: >> >> 0.40, 0.30, 0.20, 0.10 > > library(rgeos) > gArea(spoly1) > gArea(gIntersection(spAll, spoly1, byid=TRUE), byid=TRUE)/gArea(spoly1) > > but note the warnings. You'll need to project both objects to get a proper > measure. > > Roger > >> >> Thanks >> Ross >> >> >> >> [[alternative HTML version deleted]] > > -- > Roger Bivand > Department of Economics, NHH Norwegian School of Economics, > Helleveien 30, N-5045 Bergen, Norway. > voice: +47 55 95 93 55; fax +47 55 95 95 43 > e-mail: roger.biv...@nhh.no > _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo