[R-sig-Geo] Variogram modeling

[Edzer Pebesma]

I would say that strong spatial trends can be seen, by eye, when you
plot your data in a map.

On 02/18/2014 06:43 PM, Moshood Agba Bakare wrote:
> Thanks for the response. I used to determine the presence of strong spatial
> trend by visualizing the semivariogram plot of empirical data. If the plot
> increases without level off, then I assume there is a strong spatial trend.
> Am I right with this approach? Is there a better way of detecting if there
> is a *strong spatial trend*?
> 
> Thank you.
> 
> 
> On Tue, Feb 18, 2014 at 10:19 AM, Edzer Pebesma <
> edzer.pebesma at uni-muenster.de> wrote:
> 
>>
>>
>> On 02/18/2014 06:11 PM, Moshood Agba Bakare wrote:
>>> Dear All,
>>> In my yield data, I have longitude and latitude as spherical coordinates
>>> which are converted into projected coordinates - easting and northing for
>>> variogram modelling, yield as attribute variable, and elevation.
>>> I fitted my empirical variogram as
>>> empvar<-variogram(yield~1,canmod.sp,cutoff=600,width=3, cressie=TRUE).
>>> In some documents I come across, some fitted the model using easting and
>>> northing as covariate to yield as
>>> yield ~easting+northing rather than yield ~1.
>>> which one do you advise me to use yield ~easting+northing or yield ~1.
>>
>> If there is a strong spatial trend, general advice is to work on the
>> residuals (~easting+northing), and use the same equation in the kriging
>> step (universal or regression kriging).
>>
>> You could try both, if the difference is small, I'd suggest to not
>> detrend (ie., use ~1)
>>
>> --
>> Edzer Pebesma
>> Institute for Geoinformatics (ifgi), University of Münster
>> Heisenbergstraße 2, 48149 Münster, Germany. Phone: +49 251
>> 83 33081 http://ifgi.uni-muenster.de GPG key ID 0xAC227795
>>
>>
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>>
>>
> 

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Heisenbergstraße 2, 48149 Münster, Germany. Phone: +49 251
83 33081 http://ifgi.uni-muenster.de GPG key ID 0xAC227795

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