[R-sig-Geo] Indicator Simulation Help

[Edzer Pebesma]

On 11/07/2012 09:24 PM, Katherine Lockhart wrote:
> Hi There,
> I am trying to do conditional indicator simulation on some TCE values
> in groundwater.
> I set my data up as a SpatialPointsDataFrame and expanded a grid to
> predict to that is a SpatialPixelsDataFrame.
> 
>>From there, here is my code:
> for(i in 1:length(data$TCE_.mg.L.)) (if(data$TCE_.mg.L.[i]<=0.005)
> data$TCE_.mg.L.ind[i] = 1 else
> data$TCE_.mg.L.ind[i] = 0)
> #Compute and plot the sample variogram for the indicator transform
> TCE.var<-variogram(TCE_.mg.L.ind~1, data)
> plot(TCE.var)
> #Set initial choice of variogram model
> # calculate variance as estimate of the sill
> var(data$TCE_.mg.L.ind)
> # [1] 0.2491694
> TCE.vgm<-vgm(.25, "Sph", 40)
> TCE.model<-fit.variogram(TCE.var, TCE.vgm)
> TCE.model
> #  model     psill    range
> #1   Sph 0.2770698 50.82271
> # try gstat and predict.gstat for simulation
> g <- gstat(id = "TCE_.mg.L.ind", formula = TCE_.mg.L.ind~1,data =
> data,model=TCE.model)
> class(g)
> #[1] "gstat" "list"
> TCE.sim<-predict.gstat(g, site1.grid,nsim=1,indicators=TRUE)
> summary(TCE.sim)
> #Object of class SpatialPixelsDataFrame
> #Coordinates:
> # min max
> #x  90 110
> #y  75  85
> #Is projected: NA
> #proj4string : [NA]
> #Number of points: 231
> #Grid attributes:
> # cellcentre.offset cellsize cells.dim
> #x                90        1        21
> #y                75        1        11
> #Data attributes:
> #  Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
> #0.00000 0.00000 0.00000 0.09524 0.00000 1.00000
> 
> My issue is how to get the simulated values for each pixel. I tried
> TCE.sim[1] and I just get a list of the coordinates in X and Y. I also

TCE.sim[[1]]

> need to extract the value of the mean. Also, the output seems off to
> me, does this look typical of indicator simulation? If I plot with
> spplot(TCE.sim[1]) I get a plot with just zeros and 1s. From my
> understanding, indicator simulation gives values between 0-1.

No - indicator kriging does, simulation simulates data, data are
supposed to be 0 or 1.

 Any
> advice is appreciated!
> Thank you!
> Katie
> 
> --
> Katherine Lockhart
> Graduate Student Researcher
> UC Davis
> Department of Land, Air, and Water Resources
> 
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> 

-- 
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