Transforms a probability-density utilisation distribution (UD) into its cumulative-volume representation: each cell's value becomes the fraction of the distribution contained in cells of equal or higher density. A cell value of v in the output means "this cell is inside the v-volume contour, together with all denser cells".
Arguments
- x
A single-layer or multi-layer
terra::SpatRasterrepresenting one or more UDs. Cells should be non-negative; the UD need not sum exactly to 1 (it is renormalised per layer internally).
Value
A terra::SpatRaster with the same geometry as x, cell
values replaced by their cumulative-volume quantile, and layer
names preserved. NA cells stay NA.
Details
This is the move2 analogue of move::getVolumeUD(). It is a
reshape of the raster only — no re-estimation — so it is cheap
and can be applied liberally to already-computed UDs.
References
Seaman, D. E., & Powell, R. A. (1996). An evaluation of the accuracy of kernel density estimators for home range analysis. Ecology, 77(7), 2075-2085. doi:10.2307/2265701
See also
mt_dbbmm_ud(), mt_dbgb_ud() for computing UDs;
terra::contour() for isopleth extraction from a volume UD.
Examples
if (FALSE) { # \dontrun{
library(move2)
library(sf)
fishers <- mt_read(mt_example())
fishers <- fishers[!st_is_empty(fishers), ]
leroy <- fishers[mt_track_id(fishers) == "M4", ][seq_len(200), ]
leroy <- st_transform(leroy, mt_aeqd_crs(leroy))
ud <- mt_dbbmm_ud(leroy, location_error = 20, raster = 100)
vud <- ud_volume(ud)
## draw the 50% and 95% contours of the volume UD
terra::plot(vud)
terra::contour(vud, levels = c(0.5, 0.95), add = TRUE)
## solid 50% core-area mask
core50 <- vud <= 0.5
} # }