Distance and wind covariates around a contamination source

Builds covariate rasters describing the position of every cell relative to a point source of contamination (e.g. a smelter chimney). They can be used as external drift in [krige_soil()]:

`log10_dist`: the log10 of the distance (m) to the nearest source. Atmospheric deposition typically decreases as a power law of the distance, i.e. linearly in log-log scale.
`wind`: (only if `wind_rose` is given) the frequency of the wind sector in which the cell lies, seen from the source. Cells lying downwind of the dominant winds receive more deposition.

Usage

source_covariates(template, source, wind_rose = NULL, min_dist = NULL)

Arguments

template: A `SpatRaster` defining the grid.
source: An `sf` / `sfc` POINT object: location(s) of the source(s). Must be a single point when `wind_rose` is used.
wind_rose: Optional `data.frame` with columns `direction` (centre of the sector, in degrees clockwise from the North, as seen from the source) and `freq` (wind frequency, any unit). Each cell gets the `freq` of the closest sector direction.
min_dist: Numeric. Distances below this value are set to `min_dist` (avoids `log10(0)` at the source). Default: the cell size.

Value

A `SpatRaster` with layers `log10_dist` and, optionally, `wind`.

Examples

data(soil_metaleurop)
grid <- soil_grid(soil_metaleurop, res = 100)
smelter <- sf::st_sfc(sf::st_point(c(701156, 7036799)), crs = 2154)
cov <- source_covariates(grid, smelter)
terra::plot(cov)