working with Z values in spatial data frames

Hello Michael,

Thank you very much for providing this suggested approach.  I'm in the
process of studying the code now to understand what it is doing and to
prepare my data for use.

Is there a way to use a polygon layer represented by a shapefile and use the
SpatialPoints data set to color code the polygonal units in the former?

Steve


On 11/5/07, Michael Sumner <mdsumner at utas.edu.au> wrote:
  

Here's one simple way, using package akima:


library(sp)

data(meuse)

## assume your data is Spatial*

coordinates(meuse) <- ~x+y



## use "elev" column in akima
library(akima)

## define a grid
xx <- coordinates(meuse)[,1]
yy <- coordinates(meuse)[,2]
## modify offset of 100 to match your data, or use a proportion
grd <- expand.grid(x = seq(min(xx) - 200,  max(xx) + 200, length = 100),
         y = seq(min(yy) - 200, max(yy) + 200, length = 100))


res <- interpp(xx, yy, meuse$elev, grd$x, grd$y)
res <- as.data.frame(res) ## akima output is a list of 3 equal-length
vectors like grd passed in


## if you want to interpolate on another "Z", repeat as desired, adding
to output
res$cadmium <- interpp(xx, yy, meuse$cadmium, grd$x, grd$y)$z


coordinates(res) <- ~x+y
gridded(res) <- TRUE

## if you don't have a lot of empty cells
fullgrid(res) <- TRUE

image(res, "z")

## confirm where the high values were
points(meuse$x, meuse$y, cex = meuse$elev/5)

image(res, "cadmium")  ## etc

spplot(res)




Steve Friedman wrote:
    

Hi,

I have a spatial data set consisting of several z values and UTM
coordinates.  Can someone direct me to documentation describing how I
      

can
    

plot specific z values using the coordinates to develop a continuous
      

surface
    

map?

Thanks
Steve

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