[R-sig-Geo] adehabitatHR functions estUDm2spixdf & kernelUD

[Clare Death]

Hello,

I am calculating the utilisation distribution (UD) for a group of mammals (n = 37), in order to define their individual exposure to an environmental contaminant. I need to know the meaning of the value returned in each cell of the converted UD output, as I need to multiply this by the contaminant levels in those cells. It is difficult to be certain what each cell value represents.

I have two questions - thank-you for any assistance:

1) When using the estUDm2spixdf conversion: What does the function return for each cell? The probability that an animal will be found in the cell, the number of fixes per cell, the number of fixes per unit area, or a 1 or 0 flag to identify if the animal is present or absent from the cell, or something else?

2) Does the grid parameter of the kernelUD script reflect the cell dimensions of the total grid area (i.e. an arbitrary value for resolution of the pixels)? In the code below I’ve entered grid = 125. Does this mean that a grid is constructed where there are 125 cells in the horizontal dimension and 125 in the vertical (i.e. 125 * 125 = 15625 cells in total).

Some example script:
spat_dat.spdf <- SpatialPointsDataFrame(spat_dat[,6:7], spat_dat)
kud <- kernelUD(xy = spat_dat.spdf[,1], h = "href", same4all = TRUE, grid = 125)
kud.spdf <- estUDm2spixdf(kud)

Kind regards,
Dr. Clare Death
Faculty of Veterinary and Agricultural Sciences
The University of Melbourne, Australia


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