rWind (version 0.4.1)

flow.dispersion: Compute flow-based cost or conductance

Description

flow.dispersion computes movement conductance through a flow either, sea or wind currents. It implements the formula described in Fel<U+00ED>cisimo et al. 2008:

Usage

flow.dispersion(dl, sl, type = "passive", output = "raw")

Arguments

dl

Direction layer. Raster layer obtained from wind2raster function ("rWind" package) with flow direction values.

sl

Speed layer. Raster layer obtained from wind2raster function ("rWind" package) with flow speed values.

type

Could be either "passive" or "active".In "passive" mode, movement against flow direction is not allowed (deviations from the wind direction higher than 90). In "active" mode, the movement can go against flow direction, by increasing the cost.

output

This argument allows to select diferent kinds of output. "raw" mode creates a matrix (class "dgCMatrix") with transition costs between all cells in the raster. "transitionLayer" creates a TransitionLayer object with conductance values to be used with "gdistance" package.

Value

In "transitionLayer" output, the function returns conductance values (1/cost)to move betwen all cells in a raster having into account flow speed and direction obtained from wind.fit function("rWind" package). As wind or sea currents implies directionality, flow.dispersion produces an anisotropic conductance matrix (asimetric). Conductance values are used later to built a TransitionLayer object from "gdistance" package.

In "raw" output, flow.dispersion creates a sparse Matrix with cost values.

Details

Cost=(1/Speed)*(HorizontalFactor)

being HorizontalFactor a "function that incrementaly penalized angular deviations from the wind direction" (Felic<U+00ED>simo et al. 2008).

References

Felic<U+00ED>simo, <U+00C1>. M., Mu<U+00F1>oz, J., & Gonz<U+00E1>lez-Solis, J. (2008). Ocean surface winds drive dynamics of transoceanic aerial movements. PLoS One, 3(8), e2928.

Jacob van Etten (2017). R Package gdistance: Distances and Routes on Geographical Grids. Journal of Statistical Software, 76(13), 1-21. doi:10.18637/jss.v076.i13

See Also

wind.fit, wind2raster

Examples

# NOT RUN {
 require(gdistance)

 w<-wind.dl(2015,2,12,0,-10,5,35,45)

 data(wind_data)
 w<-wind.fit(wind_data)

 dl<-wind2raster(w)
 sl<-wind2raster(w, type="speed")

 Conductance<-flow.dispersion(dl,sl,"passive", "transitionLayer")

# transitionMatrix(Conductance)
# image(transitionMatrix(Conductance))

# }