[R-sig-Geo] RE : Inverse Distance Weighting and Treating kriged data before cross validation

[Edzer Pebesma]

mykrige.cv = gstat:::krige.cv.spatial
mykrige.cv = edit(mykrige.cv)

then, you will find out that you will have to do the same with gstat.cv, 
and that gstat.cv is rather cryptic as it deals with cokriging of which 
ordinary kriging is a special case.

Maybe it wasn't such a good idea after all if you're new to R, sorry.

Tobin Cara wrote:
> Hello Prof. Pebesma,
>
> I would like to use leave-one-out cross validation to have a fair comparison with my other methods. 
>
> Could you explain further how to copy krige.cv to my own function and modify? Can I open up the krige.cv code somewhere? I am still new to R.
>
> Thank you in advance,
>
> Cara
> ________________________________________
> De : Edzer Pebesma [edzer.pebesma at uni-muenster.de]
> Date d'envoi : vendredi, 15. janvier 2010 12:14
> À : Tobin Cara
> Cc : r-sig-geo at stat.math.ethz.ch
> Objet : Re: [R-sig-Geo] Inverse Distance Weighting and Treating kriged data before cross validation
>
> Dear Cara,
>
> one way would be to copy krige.cv to your own function and modify this;
> I would recommend this if you want leave-one-out cross validation.
>
> If n-fold cross validation is good enough for a few folds, e.g. because
> you have plenty of data, then I would do the whole procedure "manually",
> using predict, krige or idw on the points of a particular fold using the
> data from the remaining folds.
> --
> Edzer
>
>
> Tobin Cara wrote:
>   
>> Hello,
>>
>> I am using inverse distance weighting with gstat for temperature just to compare it with other kriging methods. For a temperature field, I have removed the elevation effect at the stations by normalizing all stations to the lowest with a lapse rate of -6.5 deg C /1000 m.
>>
>> Now, I want to krig the normalized data and then add back the lapse rate multiplied by the difference in elevation to get the real temperatures at all real elevations. However, how can I do this before cross validation?
>>
>> I only know cross validation with the following command where it does not allow manipulation of the kriged field before cross validation:
>>
>> crossval_idw <- krige.cv(Temp93hr~1, DataCoordhr)
>>
>> Thank you in advance for your help.
>>
>> Cheers,
>>
>> Cara
>>
>>       [[alternative HTML version deleted]]
>>
>> _______________________________________________
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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.52north.org/geostatistics      e.pebesma at wwu.de

-- 
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.52north.org/geostatistics      e.pebesma at wwu.de