Buffer coastlines

Question

I'm trying to generate a coastline buffer by using st_buffer() with data from the  rnaturalearth library. However, when I create the buffer, it extends outside the realm of the projection, rather than wrapping around to to the other "side." This creates problems for downstream shape use. Other coastline buffer problems (e.g. 1, 2) on GIS SE have not involved issues of projection edges or not been in R.
library(rgdal)
library(rnaturalearth)
library(sf)
library(ggplot2)

robin = CRS("+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs")

ROI = ne_countries(returnclass = 'sf') %>%
  st_combine() %>%
  st_transform(robin)
coastalWaters = ROI %>%
  st_buffer(500000)
ggplot() +
  geom_sf(data = coastalWaters, fill = "lightblue", col = "transparent") +
  geom_sf(data = ROI)

The reproducible code above leads to a plot that looks like this (red circles annotated by me):

So, my question is, how can I buffer a global set of polygons with an "understood" wrapping? Solutions will preferably use the sf library of functions.

Roger-123 · Accepted Answer

Edit: added picture of result

As FSimardGIS mentioned in the comments, the key here is to use st_wrap_dateline. The trick is that you can't use st_transformation before creating the buffer because (I think) it converts it to the projection's coordinates, not the lat/lon which st_wrap_dateline requires.

st_buffer then wants the buffer distance in arc degrees, so I threw in a quick calculation to convert km to arc seconds, but might need to be refined.

I then added coord_sf to ggplot so that ggplot could do the projection for the visual.

library(rgdal)
library(rnaturalearth)
library(sf)
library(ggplot2)

robin = CRS("+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs")

ROI = ne_countries(returnclass = 'sf') %>%
  st_combine() 

#Please check the math on this part.
#KM/earth circumference * degrees in circle
buffer_in_km <- 500
buffer_as_arc_degrees<- buffer_in_km/40075*360

coastalWaters = ROI %>%
  st_buffer(buffer_as_arc_degrees)  %>% st_wrap_dateline()

ggplot() +
  geom_sf(data = coastalWaters, fill = "lightblue", col = "transparent") +
  geom_sf(data = ROI) +
  coord_sf(crs = robin)

Buffer coastlines

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