[GRASS-stats] universal kriging with spgrass6

[Edzer Pebesma]

Mathieu, that could very well be the case. Note that x+y do not
"generally" refer to x- and y-coordinates, but are the actual names of
the coordinates (or something else). From your example I cannot find out
whether the coordinates are named x and y. In addition, they should have
identical names in sitesR and mask_SG.

Best regards,
--
Edzer

mathieu grelier wrote:

Dear all,
I am trying to achieve universal kriging with GRASS and R through spgrass6
package.
Maybe you could help me to find the right R syntax.
As in the gstat doc, the polynomial I try to use for now is "x+y"

> Dear all,
> I am trying to achieve universal kriging with GRASS and R through spgrass6
> package.
> Maybe you could help me to find the right R syntax.
> As in the gstat doc, the polynomial I try to use for now is "x+y"
>
> In R, with automap package, this works :
>   
>> data(meuse)
>> coordinates(meuse) = ~x+y
>> data(meuse.grid)
>> gridded(meuse.grid) = ~x+y
>> column = "zinc"
>>     
> ##Ordinary kriging :
>   
>> predictors = "1"
>> autoKrige(as.formula(paste(column,"~", predictors)), meuse, meuse.grid)
>>     
> ##Universal kriging :
>   
>> predictors = "x+y"
>> autoKrige(as.formula(paste(column,"~", predictors)), meuse, meuse.grid)
>>     
>
> But using spgrass6, it becomes (some steps have been skipped):
>   
>> sitesR <- readVECT6("grass_sites")
>>     
> ...
>   
>> mask_SG <- SpatialGridDataFrame(grd, data=data, CRS(G$proj4))
>>     
> ...
>
> ##Ordinary kriging => WORKS:
>   
>> predictors = "1"
>> kriging_result = autoKrige(as.formula(paste(column,"~",predictors)),
>>     
> sitesR, mask_SG)
>
> ##Universal kriging => ERROR:
>   
>> predictors = "x+y"
>> kriging_result = autoKrige(as.formula(paste(column,"~",predictors)),
>>     
> sitesR, mask_SG)
>   
>> Error in eval(expr, envir, enclos) : "x" object not found
>>     
>
> Why can't we use the x an y columns here?
> Maybe it is because the meuse and sites R data.frames don't have the same
> structure ?
>   
>> class(meuse)
>>     
> [1] "data.frame"
>   
>> attributes(meuse)
>>     
> $names
>  [1] "x"       "y"       "cadmium" "copper"  "lead"    "zinc"    "elev"
>   
>> class(sitesR)
>>     
> [1] "SpatialPointsDataFrame"
>   
>> attributes(sitesR)
>>     
> $bbox
> ...
> $proj4string
> ...
> $coords
> ...
> $data
>            site value cat        x       y
> 1Ai      81.80   1 825094.9 6796083
> 2     Al      38.50   2 758780.4 6851508
> 3     Ar     103.50   3 818973.3 6796125
> 4           Av      52.50   4 775136.0 6877271
> ...
>
>   
> ------------------------------------------------------------------------
>
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>   

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de/
http://www.springer.com/978-0-387-78170-9 e.pebesma at wwu.de