`get_dist_focus()` generates a distance map from focus locations.
get_dist_focus(window, lon, lat, resolution, mile = FALSE, preprocess = FALSE)an im object
owin object
vector of longitudes
vector of latitudes
resolution of raster objects
logical. `mile` specifies whether to return the output in miles instead of kilometers (by default, FALSE).
logical. `preprocess` specifies whether to first pick the potentially closest point. It is recommended to set `preprocess = TRUE` if users need to obtain distances from many points.
`get_dist_focus()` depends on `geosphere::distVincentyEllipsoid()`. Since it calculates accurate distances considering the ellipsoid, the process sometimes becomes computationally demanding, namely when we need to obtain distances from many points. In that case, users can set `preprocess = TRUE`. With this option, `get_dist_focus()` calculates distances from points by first identifying the closest point using `sf::st_nearest_feature()` with approximations. This process is more efficient than computing distances from all the points with `geosphere::distVincentyEllipsoid()` and then obtaining the minimum of all the distances. By default, `get_dist_focus()` returns distances in kilometers unless users set `mile = TRUE`.