mcStewart: Stewart Potentials Parallel

In Groupe-ElementR/SpatialPosition: Spatial Position Models

Stewart Potentials Parallel

Description

This function computes Stewart potentials using parallel computation.

Usage

mcStewart(
  knownpts,
  unknownpts,
  varname,
  typefct = "exponential",
  span,
  beta,
  resolution,
  mask,
  cl,
  size = 1000,
  longlat = TRUE,
  returnclass = "sp"
)

Arguments

knownpts	sp or sf object; this is the set of known observations to estimate the potentials from.
unknownpts	sp or sf object; this is the set of unknown units for which the function computes the estimates. Not used when resolution is set up. (optional)
varname	character; name of the variable in the knownpts dataframe from which potentials are computed. Quantitative variable with no negative values.
typefct	character; spatial interaction function. Options are "pareto" (means power law) or "exponential". If "pareto" the interaction is defined as: (1 + alpha * mDistance) ^ (-beta). If "exponential" the interaction is defined as: exp(- alpha * mDistance ^ beta). The alpha parameter is computed from parameters given by the user (beta and span).
span	numeric; distance where the density of probability of the spatial interaction function equals 0.5.
beta	numeric; impedance factor for the spatial interaction function.
resolution	numeric; resolution of the output SpatialPointsDataFrame (in map units). If resolution is not set, the grid will contain around 7250 points. (optional)
mask	sp or sf object; the spatial extent of this object is used to create the regularly spaced points output. (optional)
cl	numeric; number of clusters. By default cl is determined using parallel::detectCores().
size	numeric; mcStewart splits unknownpts in chunks, size indicates the size of each chunks.
longlat	logical; if FALSE, Euclidean distance, if TRUE Great Circle (WGS84 ellipsoid) distance.
returnclass	"sp" or "sf"; class of the returned object.

Details

The parallel implementation splits potentials computations along chunks of unknownpts (or chunks of the grid defined using resolution).

Value

Point object with the computed potentials in a new field named OUTPUT.

See Also

stewart.

Examples

## Not run: 
if(require(cartography)){
  nuts3.spdf@data <- nuts3.df
  t1 <- system.time(
    s1 <- stewart(knownpts = nuts3.spdf,resolution = 40000,
                  varname = "pop2008",
                  typefct = "exponential", span = 100000,
                  beta = 3, mask = nuts3.spdf, returnclass = "sf")
  )
  t2 <- system.time(
    s2 <- mcStewart(knownpts = nuts3.spdf, resolution = 40000,
                    varname = "pop2008",
                    typefct = "exponential", span = 100000,
                    beta = 3, mask = nuts3.spdf, cl = 3, size = 500, 
                    returnclass = "sf")
  )
  identical(s1, s2)
  cat("Elapsed time\n", "stewart:", t1[3], "\n mcStewart:",t2[3])
  
  iso <- isopoly(x = s2, 
                 breaks = c(0,1000000,2000000, 5000000, 10000000, 20000000, 
                            200004342),
                 mask = nuts3.spdf, returnclass = "sf")
  # cartography
  opar <- par(mar = c(0,0,1.2,0))
  bks <- sort(unique(c(iso$min, iso$max)))
  choroLayer(x = iso, var = "center", breaks = bks, border = NA,
             legend.title.txt = "pop")
  layoutLayer("potential population", "","", scale = NULL)
  par(opar)
}

## End(Not run)

Groupe-ElementR/SpatialPosition documentation built on Sept. 14, 2023, 6:14 a.m.