On Thu, 7 Jun 2007, Don MacQueen wrote: > I don't know enough to assess whether I have a misunderstanding or a mistake. > > spsample() with type='random' is giving an error, but succeeding with > type='stratified'. > > Maybe random sampling requires projection information and stratified doesn't? > I may have constructed my SpatialPolygonsDataFrame incorrectly?
The problem is that the hole well-nigh fills the polygon, and after iter=4 tries, it tries to finish, and fails, because the output object is NULL rather than some points. Increasing iter= doesn't help. It shouldn't do this, but it does - I'll try to fix it but not soon. A work-around is: plot(SP) r1 <- spsample(as(SP, "Spatial"), type="random", n=300) points(r1) r2 <- overlay(SP, r1) points(r1[!is.na(r2)], col="red") length(which(!is.na(r2))) >= 50 r3 <- sample(which(!is.na(r2)), 50) length(r3) points(r1[r3], pch=19, col="red") Most likely spsurvey and/or making an appropriate window in spatstat will do this better. Thanks for a clear report that was easy to reproduce. Roger > > Thanks > -Don > > Details: > > spgd consists of two rectangles, one inside the other, and the inside > one is a hole. > The outer one has vertices in counter-clockwise order; the inner one > in clockwise order. > > > class(tst) > [1] "SpatialPolygonsDataFrame" > attr(,"package") > [1] "sp" > > > summary(tst) > Object of class SpatialPolygonsDataFrame > Coordinates: > min max > r1 990396.8 990762.3 > r2 213369.4 213702.6 > Is projected: NA > proj4string : [NA] > Data attributes: > ID > zone:1 > > > > stst <- spsample(tst,type='stratified',n=50) > > plot(tst) > > points(stst) > > stst <- spsample(tst,type='random',n=50) > Error in `proj4string<-`(`*tmp*`, value = <S4 object of class "CRS">) : > proj4string only works for class(es extending) Spatial > > > ########## > > sessionInfo() > R version 2.5.0 (2007-04-23) > powerpc-apple-darwin8.9.1 > > locale: > C > > attached base packages: > [1] "stats" "graphics" "grDevices" "utils" "datasets" > "methods" "base" > > other attached packages: > maptools sp foreign rmacq > "0.6-12" "0.9-14" "0.8-20" "1.0" > > ########## > ## since tst is fairly small, here it is: > ########## > > tst > An object of class "SpatialPolygonsDataFrame" > Slot "data": > ID > zone zone > > Slot "polygons": > [[1]] > An object of class "Polygons" > Slot "Polygons": > $zn > An object of class "Polygon" > Slot "labpt": > [1] 990579.4 213536.2 > > Slot "area": > [1] 64601.13 > > Slot "hole": > [1] FALSE > > Slot "ringDir": > [1] 1 > > Slot "coords": > x y > [1,] 990499.3 213702.6 > [2,] 990762.3 213559.8 > [3,] 990658.2 213369.4 > [4,] 990396.8 213513.2 > [5,] 990499.3 213702.6 > > > $zn2 > An object of class "Polygon" > Slot "labpt": > [1] 990584.4 213537.3 > > Slot "area": > [1] 30367.20 > > Slot "hole": > [1] TRUE > > Slot "ringDir": > [1] -1 > > Slot "coords": > x y > [1,] 990492.6 213650.8 > [2,] 990441.8 213549.4 > [3,] 990673.3 213423.7 > [4,] 990728.1 213525.6 > [5,] 990492.6 213650.8 > > > > Slot "plotOrder": > [1] 1 2 > > Slot "labpt": > [1] 990579.4 213536.2 > > Slot "ID": > [1] "zone" > > Slot "area": > [1] 94968.33 > > > > Slot "plotOrder": > [1] 1 > > Slot "bbox": > min max > r1 990396.8 990762.3 > r2 213369.4 213702.6 > > Slot "proj4string": > CRS arguments: NA > > -- Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: [EMAIL PROTECTED] _______________________________________________ R-sig-Geo mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
