flow.dispersion: Compute flow-based cost or conductance
In rWind: Download, Edit and Include Wind and Sea Currents Data in Ecological and Evolutionary Analysis

Description Usage Arguments Details Value Note Author(s) References See Also Examples

flow.dispersion computes movement conductance through a flow either, sea or wind currents. It implements the formula described in Felícisimo et al. 2008:

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cost.FMGS(wind.direction, wind.speed, target, type = "active")

flow.dispersion(x, fun = cost.FMGS, output = "transitionLayer", ...)

`wind.direction`	A vector or scalar containing wind directions.
`wind.speed`	A vector or scalar containing wind speeds.
`target`	direction of the target cell
`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.
`x`	RasterStack object with layers obtained from wind2raster function ("rWind" package) with direction and speed flow values.
`fun`	A function to compute the cost to move between cells. The default is `cost.FMGS` from Felicísimo et al. (2008), see details.
`output`	This argument allows to select different 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.
`...`	Further arguments passed to or from other methods.

Cost=(1/Speed)*(HorizontalFactor)

being HorizontalFactor a "function that incrementally penalized angular deviations from the wind direction" (Felicísimo et al. 2008).

In "transitionLayer" output, the function returns conductance values (1/cost)to move between 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 (asymmetric). 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.

Note that for large data sets, it could take a while. For large study areas is strongly advised perform the analysis in a remote computer or a cluster.

Javier Fernández-López; Klaus Schliep; Yurena Arjona

Felicísimo, Á. M., Muñoz, J., & González-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

wind.dl, wind2raster

require(gdistance)

data(wind.data)

wind <- wind2raster(wind.data)

Conductance <- flow.dispersion(wind, type = "passive")

transitionMatrix(Conductance)
image(transitionMatrix(Conductance))