[R-sig-Geo] variogram with nominal data

[Edzer Pebesma]

Indeed, the usual approach is to use multiple indicators. You'll find an
example for different thresholds of a continuous variable in the end of
the following demo script.

library(gstat)
demo(cokriging)
--
Edzer

On 06/12/2010 05:16 AM, ashton at msu.edu wrote:
> Hi Julian, and list,
> 
> the variogram calculates the average squared difference between z-values separated by particular lags. Calculating differences with nominal data, and certainly IDs, is wrong. You will get results, but garbage in, garbage out applies here.
> 
> That said, you can calculate indicator variograms on nominal data. See a recent paper by Ola Ahqvist and myself, or other papers, mostly in soil science. (What fun to self-cite!): 
> Spatial and semantic dimensions of landscape heterogeneity, Landscape Ecology (2010).
> 
> I don't think the gstat variogram functionality for nominal data extends to more than two binary classes, but is not hard to implement more than that. I have R script on my machine at work if you would be interested.
> 
> Hope this helps,
> 
> Ashton Shortridge
> 
> Quoting Julien Beguin <julien.beguin.1 at ulaval.ca>:
> 
>> Dear list,
>>
>> I would like to evaluate spatial dependence for about 10000 spatial 
>> data points. However, the variable associated with those points is 
>> not continuous as in the data "meuse" but is a land cover type (e.g. 
>> WATER). What should I consider as variable Z in the variogram() 
>> function with gstat? is it right to take the ID of each point as in 
>> the code below?
>> -----------------------------------------------------------------------------
>> Z <- data.frame[ which(data.frame$landcover=='WATER'),]$ID
>> X <- frame$X
>> Y <- frame$Y
>> mydata1 <- data.frame(Z, X, Y);
>> coordinates(mydata1) <- c("X", "Y");
>> vario01 <- variogram(Z~1, mydata1, cutoff=50000, alpha=c(0,45,90,135))
>> ------------------------------------------------------------------------------
>>
>> Any advice would be very appreciated. Thank you for your time,
>>
>> Julien Beguin
>> ------------------
>> Ph.D. student
>> Laval University
>> Québec, Canada
>>
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>>
>>
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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