This is the first time I'm using ko-kriging in gstat. My problem is that
I'm not sure how to prepare the data frame to supply to co-kriging when the
variable of interest and auxiliary variables are not measured at the same
locations.
Data frame with the variable of interest, z_ar, is voi_gs
> head(voi_gs)
x y z_ar
8974 312216.6 530439.8 49.03470
8283 312084.6 530559.8 57.15355
5057 311772.6 530883.8 49.13453
1551 311976.6 531207.8 44.73679
10116 312168.6 530163.8 50.45549
6155 312528.6 530787.8 62.70750
Data frame with the auxiliary variable, z_ptsis aux_gs
> head(aux_gs)
x y z_pts
9564 312198.6 530313.8 75.91368
6584 311766.6 530745.8 38.87462
2138 311562.6 531153.8 58.62555
9110 312534.6 530421.8 68.35654
9525 312366.6 530325.8 54.26653
7497 311442.6 530649.8 38.95024
I combined them into one data frame to supply to variogram() and
krige() functions.
Since non of the locations are same between voi_gs and aux_gs, I introduced
NA values and combined them in the following way
> aux_gs$z_ar=NA
> voi_gs$z_pts=NA
> comb_gs=rbind(aux_gs,voi_gs)
> head(comb_gs)
x y z_pts z_ar
9564 312198.6 530313.8 75.91368 NA
6584 311766.6 530745.8 38.87462 NA
2138 311562.6 531153.8 58.62555 NA
9110 312534.6 530421.8 68.35654 NA
9525 312366.6 530325.8 54.26653 NA
7497 311442.6 530649.8 38.95024 NA
> tail(comb_gs)
x y z_pts z_ar
180 312468.6 531363.8 NA 70.54528
8633 312264.6 530511.8 NA 44.34631
7694 312492.6 530631.8 NA 57.30173
1079 312108.6 531255.8 NA 46.96482
2230 311124.6 531135.8 NA 40.36449
2201 312312.6 531147.8 NA 44.85896
and then constructing cross-variogram
> coordinates(comb_gs) = ~x+y
> g = gstat(formula=z_pts~z_ar, data=comb_gs)
> vg = variogram(g)
but variogram function does not accept NA values and gives me an error. I
know I can't have NA values in the data, but I don't know how else I can
create the data frame to construct the cross-variogram. Any help is really
appreciated. Thanks.
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