geospt (version 0.4-9)

pocket.plot: graphs the probability or standardized variance in the directions north-south or east-west

Description

The pocket-plot (so named because of its use in detecting pockets of non-stationarity) is a necessary technique to identify a localized area atypical with respect to the stationarity model. It is built to exploit the spatial nature of the data through the coordinates of rows and columns (east "X" and north "Y", respectively).

Usage

pocket.plot(data, graph, X, Y, Z, ...)

Value

returns (or plots) the pocket plot

References

Cressie, N.A.C., 1993. Statistics for Spatial Data. Wiley. Gomez, M., Hazen, K., 1970. Evaluating sulfur and ash distribution in coal seems by statistical response surface regression analysis. U.S. Bureau of Mines Report RI 7377.

Examples

# Core measurements (in \% coal ash) at reoriented locations. 
# Units on the vertical axis are \% coal ash.

# This data recording was found in mining samples originally reported by 
# Gomez and Hazen (1970), and later used by Cressie (1993). 

# This data is available in the sp and gstat packages

library(gstat) 
data(coalash) 
plot(coalash[,1:2], type="n", xlab="x", ylab="y") 
text(coalash$x,coalash$y,coalash$coalash,cex=0.6)

# Pocket plot in the north-south direction. 
# Units on the vertical axis are root (\% coal ash) 

# Plot generated with the function pocket.plot 
# Clearly rows 2, 6, and 8 are atypical 

# This serves as verification that these rows are potentially problematic

# Analysis of local stationarity in probabilities of the coal in south-north direction 

pocket.plot(coalash, "PPR", coalash$x, coalash$y, coalash$coalash)

# Analysis of local stationarity in variance of the coal in south-north direction 

pocket.plot(coalash, "PVR", coalash$x, coalash$y, coalash$coalash) 

# Analysis of local stationarity in probabilities of the coal in east-west direction 

pocket.plot(coalash, "PPC", coalash$x, coalash$y, coalash$coalash) 

# Analysis of local stationarity in variance of the coal in east-west direction 

pocket.plot(coalash, "PVC", coalash$x, coalash$y, coalash$coalash)