Another alternative might follow an example in Venables and Ripley (2002, p. 76-77) Modern Applied Statistics with S (Springer):

topo.loess <- loess(z~x*y, topo, degree=2, span=0.25)
topo.mar <- list(x=seq(0, 6.5, .2), y=seq(0, 6.5, .2))
topo.lo <- predict(topo.loess, expand.grid(topo.mar))
par(pty="s")
contour(topo.mar$x, topo.mar$y, topo.lo,
 xlab="", ylab="", levels=seq(700, 1000, 25), cex=0.7)
points(topo$x, topo$y)
par(pty="m")

They also provide a solution using contourplot. However, in R 1.9.1 alpha, I got an error on that, 'couldn't find function "mat2tr"'; it should be fairly easy to work around that error if it has not already been fixed in R 1.9.1, which I have not yet installed.

     hope this helps.  spencer graves

Barry Rowlingson wrote:

temiz wrote:

hello

is there any way creating slope angle surface from
interpolated topography surface ?


The GRASS GIS can do calculations of slope, and aspect, and so on from spot heights. Suggest you install GRASS and then maybe do data transfer from R using the GRASS package from CRAN.

Baz

Grass: http://grass.itc.it/index.html

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