fields (version 16.2)

fields.grid: Using MKrig for predicting on a grid.

Description

This is an extended example for using the sparse/fast interpolation methods in mKrig to evaluate a Kriging estimate on a large grid.

Details

mKrig is a flexible function for surface fitting using a spatial process model. It can also exploit sparse matrix methods forlarge data sets by using a compactly supported covariance. The example below shows how ot evaluate a solution on a big grid. (Thanks to Jan Klennin for this example.)

Examples

x<- RMprecip$x
y<- RMprecip$y

Tps( x,y)-> obj

# make up an 80X80 grid that has ranges of observations
# use same coordinate names as the x matrix

glist<- fields.x.to.grid(x, nx=80, ny=80) # this is a cute way to get a default grid that covers x

# convert grid list to actual x and y values ( try plot( Bigx, pch="."))
    make.surface.grid(glist)-> Bigx 

# include actual x locations along with grid. 
    Bigx<- rbind( x, Bigx)

# evaluate the surface on this set of points (exactly)

    predict(obj, x= Bigx)-> Bigy

# set the range for the compact covariance function 
# this will involve  less than 20 nearest neighbors that have
# nonzero covariance
# 

     V<- diag(c( 2.5*(glist$lon[2]-glist$lon[1]), 
                 2.5*(glist$lat[2]-glist$lat[1])))
if (FALSE) {
# this is an interplotation of the values using a compact 
# but thin plate spline like covariance. 
    mKrig( Bigx,Bigy, cov.function="wendland.cov",k=4, V=V, 
                 lambda=0)->out2 
# the big evaluation this takes about 45 seconds on a Mac G4 latop
    predictSurface( out2, nx=400, ny=400)-> look
}

# the nice surface
if (FALSE) {    
    surface( look)
    US( add=TRUE, col="white")
}