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Fig. 2.5. Best Combined Spatial Predictor.library(gstat) library(maptools) library(rgdal) library(lattice) # trellis.par.set(sp.theme()) # load data: data(meuse) coordinates(meuse) <- ~x+y # load grids: data(meuse.grid) meuse.grid$X <- meuse.grid$x meuse.grid$Y <- meuse.grid$y meuse.grid$soil <- as.factor(meuse.grid$soil) coordinates(meuse.grid) <- ~x+y gridded(meuse.grid) <- TRUE fullgrid(meuse.grid) <- TRUE # get values from grids to points: meuse.ov <- overlay(meuse.grid, meuse) meuse$X <- meuse.ov$X meuse$Y <- meuse.ov$Y meuse$soil <- meuse.ov$soil # ordinary kriging: vt.fit <- fit.variogram(variogram(log1p(zinc)~1, meuse), vgm(1, "Exp", 300, 1)) plot(variogram(log1p(zinc)~1, meuse), vt.fit) zinc.ok <- krige(log1p(zinc)~1, meuse, meuse.grid, vt.fit) zinc.ok$zinc.pred <- expm1(zinc.ok$var1.pred) zinc.ok$svar <- zinc.ok$var1.var/var(log1p(meuse$zinc)) # GLM prediction (all possible predictors): m.glm <- glm(zinc~dist+soil+ffreq+X+Y, meuse, family=poisson()) summary(m.glm) p.glm <- predict(m.glm, newdata=meuse.grid, type="response", se.fit=T) zinc.glm <- as(meuse.grid["soil"], "SpatialPointsDataFrame") zinc.glm$var1.pred <- p.glm$fit zinc.glm$var1.var <- p.glm$se.fit zinc.glm$svar <- p.glm$se.fit^2/(m.glm$null.deviance/m.glm$df.null) gridded(zinc.glm) <- TRUE fullgrid(zinc.glm) <- TRUE # Best Combined Spatial Prediction (OK and GLM): meuse.grid$zinc.BCSP <- (zinc.glm$var1.pred/zinc.glm$svar+zinc.ok$zinc.pred/zinc.ok$svar)/(1/zinc.glm$svar+1/zinc.ok$svar) # plots next to each other: spplot(meuse.grid[c("zinc.ok", "zinc.BCSP", "zinc.glm")], col.regions=grey(rev(seq(0,1,0.025))), sp.layout=list("sp.points", meuse, col="black", cex=.5))
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