Least-cost travel time surface — least

Map the least-cost wind travel time (or flow rate, its inverse) between one or more sites and every grid cell across the domain: downwind, from the sites to each cell, or upwind, from each cell to the sites. This function is a wrapper around accCost.

Usage

least_cost(rose, sites, direction = "downwind", rate = FALSE, ...)

Arguments

rose: A wind_rose(), or a wind_graph built in advance whose direction matches direction; see pairwise_least_cost().
sites: A two-column matrix (or data frame) of point coordinates, or a SpatVector of points.
direction: Either "downwind" (the default), for travel from the sites to each cell, or "upwind", for travel from each cell to the sites.
rate: Whether to return values as "rates" instead of the default "cost distances". Rates are the inverse of cost distances, representing flow rather than travel time.
...: Further arguments passed to wind_graph(), such as wrap. Not allowed when rose is already a wind_graph.

Value

A single-layer SpatRaster. With rate = FALSE, the layer is named hours and gives the travel time between each cell and the nearest site (in the given direction), in hours if trans = 1 in wind_rose() and wind speeds are in m/s (otherwise in relative units). With rate = TRUE, it is named rate and gives the inverse. Sites outside the grid are ignored, with a warning.

Details

Paths are restricted to the eight neighbor directions, so cost distances are overestimated for routes between neighbor bearings; see pairwise_least_cost for magnitudes. Sites are snapped to the centers of their grid cells.

Examples

rose <- windscape_example("wind_rose")
site <- cbind(-105, 40)
from_site <- least_cost(rose, site)
to_site <- least_cost(rose, site, direction = "upwind")
terra::plot(c(from_site, to_site), main = c("from the site", "to the site"))