我试图用ggplot和sf得到一条表示地球仪边缘的线（或者一个表示海洋的多边形）。我的代码适用于一个基本的莫尔韦德投影...

library(tmap)
library(sf)
library(s2)
sf_use_s2(TRUE) 
data("World") ## get built-in data from the tmap package
world.sf <- World

lat <- c(seq(from=-90,to=90,by=0.25)) ## creates a sequence -90 to 90 by 0.25
lon <- c(rep(180,length(lat)),rep(-180,length(lat))) # creates a sequence of 180 and -180 longitudes
oceans.df <- data.frame("lon"=lon, "lat"=c(lat,lat)) ## combines the point in a data frame
oceans.sf <- st_as_sf(oceans.df,coords = c("lon","lat"), crs=4326) %>% 
  st_union() %>% # combines the points into a MULTIPOINT
  st_convex_hull() # gets the outline of the points

ggplot() + 
  geom_sf(data=oceans.sf, fill="blue") ## fine for Mercator

oceans_moll.sf <- st_as_sf(oceans.df,coords = c("lon","lat"), crs=4326) %>% 
  st_transform(crs="+proj=moll") %>% ## 
  st_union() %>% # combines the points into a MULTIPOINT
  st_convex_hull() # gets the outline of the points

world_moll.sf <- st_transform(world.sf, crs="+proj=moll")
ggplot() + 
  geom_sf(data=oceans_moll.sf, fill="blue") + 
  geom_sf(data=world_moll.sf, fill="white")

但对于以太平洋为中心的莫尔韦德来说，

oceans_moll_pacific.sf <- st_as_sf(oceans.df,coords = c("lon","lat"), crs=4326) %>% 
  st_transform(crs="+proj=moll +lon_0=-150 +x_0=0 +y_0=0") %>% ## 
  st_union() %>% # combines the points into a MULTIPOINT
  st_convex_hull() # gets the outline of the points

ggplot() + 
  geom_sf(data=oceans_moll_pacific.sf, fill="blue")

不太确定出了什么问题。我试着用下面的sf：：st_transform（）中的代码定义地球仪，返回空的几何体，但这也不适用于重投影。

ocean <- st_point(x = c(0,0)) %>%
  st_buffer(dist = 6371000) %>%
  st_sfc(crs = "+proj=ortho +lat_0=20 +lon_0=0 +x_0=0 +y_0=0 +a=6371000 +b=6371000 +units=m +no_defs")

不知道这里出了什么问题...