Project geometries to CRS centered on longitudes other than 0

recenter-sf

library(sf)
library(rnaturalearth)

# transform an sf object, moving the dateline seam to edge of projection
#
# x: sf containing spatial features
# crs: character; proj4 string for new projection
#
# return:
#   sf containing spatial features in new projection
recenter_sf <- function(x, crs) {
  stopifnot(inherits(x, c("sf", "sfc")))
  # find central meridian
  center <- as.numeric(stringr::str_extract(crs, "(?<=lon_0=)[-.0-9]+"))
  if (is.na(center) || length(center) != 1 || !is.numeric(center)) {
    stop("CRS has no central meridian term (+lon_0).")
  }
  
  # edge is offset from center by 180 degrees
  edge <- ifelse(center < 0, center + 180, center - 180)
  
  # create an very narrow sliver to clip out
  delta <- 1e-5
  clipper <- sf::st_bbox(c(xmin = edge - delta, xmax = edge + delta,
                           ymin = -90, ymax = 90),
                         crs = 4326)
  clipper <- sf::st_as_sfc(clipper)
  clipper <- suppressWarnings(smoothr::densify(clipper, max_distance = 1e-3))
  clipper <- sf::st_transform(clipper, crs = sf::st_crs(x))
  
  # cut then project
  x_proj <- sf::st_difference(x, clipper)
  sf::st_transform(x_proj, crs = crs)
}


# world map
countries <- ne_countries(returnclass = "sf") %>% 
  st_geometry()
proj <- "+proj=eqc +lat_ts=0 +lat_0=0 +lon_0=180 +x_0=0 +y_0=0 +ellps=WGS84 +units=m +no_defs"
# bad :(
countries_proj <- st_transform(countries, crs = proj)
ggplot(countries_proj) +
  geom_sf(color = "transparent", fill = "#e6e6e6") +
  theme_void()
# good :)
countries_recenter <- recenter_sf(countries, crs = proj)
ggplot(countries_recenter) +
  geom_sf(color = "transparent", fill = "#e6e6e6") +
  theme_void()