[GRASS-stats] universal kriging with spgrass6

[Edzer Pebesma]

Roger Bivand wrote:
> On Thu, 25 Jun 2009, Edzer Pebesma wrote:
>
>> 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.
>
> Yes, it is beginning to look like the names in mask_SG, isn't it? Do
> you have a view on whether degree= should be mandatory, or does the
> infrastructure recognise coordinate RHS variables and rescale them
> automatically (I doubt the latter)? Why do users use trend variables
> in this way - the range of values in the (X'X) matrix becomes enormous
> with the usual metre metric for coordinates?
Another question we could ask (ourselves) is why in R we allow users to
give their coordinates the names they like. I remember that for that
sole reason (need to rename) I added the function

coordnames(x) = c("u", "v")

to sp. In case they're called "lon" and "lat", they also don't change
name after projection. But maybe I talk too much with people worrying
about semantics, these days. ;-)
--
Edzer
>
> Roger
>
>>
>> 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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>>> grass-stats mailing list
>>> grass-stats at lists.osgeo.org
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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