R version 2.6.0 (2007-10-03)
Copyright (C) 2007 The R Foundation for Statistical Computing
ISBN 3-900051-07-0

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> library(gstat)
Loading required package: sp
> data(meuse.grid)
> gridded(meuse.grid) = ~x+y
> data(meuse)
> coordinates(meuse) = ~x+y
> 
> # choose arbitrary line over the grid:
> image(meuse.grid["dist"],axes=T)
> pp = rbind(c(180000,331000),c(180000,332000),c(181000,333500))
> Sl = SpatialLines(list(Lines(list(Line(pp)), "a")))
> plot(Sl,add=T,col='green')
> 
> # use the default spsample arguments of predict.gstat:
> pts=spsample(Sl,n=500,'regular',offset=c(.5,.5))
> plot(pts, pch=3, cex=.2, add=T)
> 
> v = vgm(.6, "Sph", 900, .06)
> out1 = krige(log(zinc)~1, meuse, Sl, v)
[using ordinary kriging]
> out1
An object of class “SpatialLinesDataFrame”
Slot "data":
         x        y var1.pred    var1.var
a 180333.3 332166.7  6.161791 0.008025042

Slot "lines":
[[1]]
An object of class “Lines”
Slot "Lines":
[[1]]
An object of class “Line”
Slot "coords":
       [,1]   [,2]
[1,] 180000 331000
[2,] 180000 332000
[3,] 181000 333500



Slot "ID":
[1] "a"



Slot "bbox":
      min    max
r1 180000 181000
r2 331000 333500

Slot "proj4string":
CRS arguments: NA 

> 
> points(180333,332167,pch=3,cex=2)
> 
> # use the same line as block discretization, and predict for (0,0)
> # (because the block discretizing points are not centered)
> out2 = krige(log(zinc)~1, meuse, SpatialPoints(matrix(0,1,2)), v, block=coordinates(pts))
[using ordinary kriging]
> out2
  coordinates var1.pred    var1.var
1      (0, 0)  6.161791 0.008025042
> 
> compare.krigingLines = function(formula, data, newdata, model) {
+ 	out1 = krige(formula, data, newdata, model)
+ 	pts = spsample(newdata, n=500, 'regular', offset=.5)
+ 	out2 = krige(formula, data, SpatialPoints(matrix(0,1,2)), model, block = coordinates(pts))
+ 	print("difference:")
+ 	as.data.frame(out1)[3:4]- as.data.frame(out2)[3:4]
+ }
> 
> compare.krigingLines(log(zinc)~1, meuse, Sl, v)
[using ordinary kriging]
[using ordinary kriging]
[1] "difference:"
  var1.pred var1.var
a         0        0
> 
> # one line, consisting of two line segments:
> pp2 = rbind(c(181000,333500),c(181000,332500))
> Sl2 = SpatialLines(list(Lines(list(Line(pp),Line(pp2)), "a")))
> krige(log(zinc)~1, meuse, Sl2, v)
[using ordinary kriging]
An object of class “SpatialLinesDataFrame”
Slot "data":
         x        y var1.pred    var1.var
a 180666.7 332583.3  6.042376 0.005319134

Slot "lines":
[[1]]
An object of class “Lines”
Slot "Lines":
[[1]]
An object of class “Line”
Slot "coords":
       [,1]   [,2]
[1,] 180000 331000
[2,] 180000 332000
[3,] 181000 333500


[[2]]
An object of class “Line”
Slot "coords":
       [,1]   [,2]
[1,] 181000 333500
[2,] 181000 332500



Slot "ID":
[1] "a"



Slot "bbox":
      min    max
r1 180000 181000
r2 331000 333500

Slot "proj4string":
CRS arguments: NA 

> compare.krigingLines(log(zinc)~1, meuse, Sl2, v)
[using ordinary kriging]
[using ordinary kriging]
[1] "difference:"
  var1.pred var1.var
a         0        0
> 
> # two seperate line segments:
> Sl3 = SpatialLines(list(Lines(list(Line(pp)), "a"),Lines(list(Line(pp2)),"b")))
> krige(log(zinc)~1, meuse, Sl3, v)
[using ordinary kriging]
An object of class “SpatialLinesDataFrame”
Slot "data":
         x        y var1.pred    var1.var
a 180333.3 332166.7  6.161791 0.008025042
b 181000.0 333000.0  5.706034 0.011042867

Slot "lines":
[[1]]
An object of class “Lines”
Slot "Lines":
[[1]]
An object of class “Line”
Slot "coords":
       [,1]   [,2]
[1,] 180000 331000
[2,] 180000 332000
[3,] 181000 333500



Slot "ID":
[1] "a"


[[2]]
An object of class “Lines”
Slot "Lines":
[[1]]
An object of class “Line”
Slot "coords":
       [,1]   [,2]
[1,] 181000 333500
[2,] 181000 332500



Slot "ID":
[1] "b"



Slot "bbox":
      min    max
r1 180000 181000
r2 331000 333500

Slot "proj4string":
CRS arguments: NA 

>