[R-sig-Geo] Interpolation / smoothing of points (without raster grids)

[Paul Hiemstra]

mike.elliott at openreach.co.uk wrote:
> Hello - can anyone suggest functions/packages that allow interpolation /
> smoothing of point data (without using raster grids)? i.e. which give
> the results at the original point locations.
>
> Many thanks, Mike Elliott.
>
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>   
If you could tell us more in detail what you want to do, we could offer 
you more guidance. To add to the promotion of packages that we wrote 
ourselves (edzer :)), you can also use automap, a package for automatic 
interpolation based on gstat and sp (two other packages). For 
cross-validation (if this is what you need) the following script will do 
the trick:

library(automap)
# Load the data
data(meuse)
coordinates(meuse) = ~x+y
data(meuse.grid)
gridded(meuse.grid) = ~x+y

# Perform cross-validation
kr.cv = autoKrige.cv(log(zinc)~1, meuse, model = c("Exp"))
kr_dist.cv = autoKrige.cv(log(zinc)~sqrt(dist), meuse,
            model = c("Exp"))
kr_dist_ffreq.cv = autoKrige.cv(log(zinc)~sqrt(dist)+ffreq,
           meuse, model = c("Exp"))
# Compare the results
compare.cv(kr.cv, kr_dist.cv, kr_dist_ffreq.cv)
compare.cv(kr.cv, kr_dist.cv, kr_dist_ffreq.cv,
           bubbleplots = TRUE)
compare.cv(kr.cv, kr_dist.cv, kr_dist_ffreq.cv,
           bubbleplots = TRUE, col.names = c("OK","UK1","UK2"))
compare.cv(kr.cv, kr_dist.cv, kr_dist_ffreq.cv,
           bubbleplots = TRUE, col.names = c("OK","UK1","UK2"),
           plot.diff = TRUE)

automap is available from CRAN.

cheers and good luck,
Paul

-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone:  +3130 274 3113 Mon-Tue
Phone:  +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul