stratify-methods {spcosa} | R Documentation |
Methods for partitioning a spatial object into compact strata by means of k-means. The objective function to minimize is the mean squared shortest distance (MSSD). Optionally, the strata may be forced to be of equal size. This facilitates field work in case of stratified simple random sampling for composites. Another option is spatial infill sampling, a variant of spatial coverage sampling where existing sampling points are taken into account. Use nTry > 1
, to reduce the risk of ending up in an unfavorable local optimum.
## S4 method for signature 'SpatialPixels': stratify(object, nStrata, priorPoints = NULL, maxIterations = 1000, nTry = 1, equalArea = FALSE, verbose = getOption("verbose")) ## S4 method for signature 'SpatialPolygons': stratify(object, nStrata, priorPoints = NULL, maxIterations = 1000, nTry = 1, nGridCells = 2500, equalArea = FALSE, verbose = getOption("verbose"))
object |
an object of class "SpatialPixels" or "SpatialPolygons" |
nStrata |
number of strata (nStrata >= 1 ). |
priorPoints |
object of class "SpatialPoints" , containing the prior (i.e., existing) points |
maxIterations |
maximum number of iterations. |
nTry |
the stratify method will try nTry initial configurations and will keep the best solution in order to reduce the risk of ending up with an unfavorable solution. |
nGridCells |
in case object is an instance of class "SpatialPolygons" , the approximate number of grid cells to be used for discretizing the vector map in object . |
equalArea |
If FALSE the algorithm results in compact strata. If TRUE , the algorithm results in compact strata of equal size. |
verbose |
if TRUE , progress information and intermediate results will be printed to the output device. |
Brus, D. J., Spatjens, L. E. E. M., and de Gruijter, J. J. (1999). A sampling scheme for estimating the mean extractable phosphorus concentration of fields for environmental regulation. Geoderma 89:129-148
de Gruijter, J. J., Brus, D. J., Bierkens, M. F. P., and Knotters, M. (2006) Sampling for Natural Resource Monitoring Berlin: Springer-Verlag.
## Not run: # read a vector representation of the `Farmsum' field (by means of rgdal-package) shpFarmsum <- readOGR(dsn = system.file("maps", package = "spcosa"), layer = "farmsum") # stratify `Farmsum' into 50 strata myStratification <- stratify(shpFarmsum, nStrata = 50) # plot the resulting stratification plot(myStratification) ## End(Not run)