CODEWITHSUNDEEP
rplotr-sfgeo
snaut
snaut

Reputation: 2535

plot geodata on the globe perspective in R

(how) is it possible to plot geodata – for example a polygon layer – on a globe with d3/perspective view, similar to this graphic on wikipedia?

I'd like a solution with sf and ggplot most, but any solutions are welcome.

(I ask this mostly out of curiosity, but since I see graphics like this fairly often, I guess the question might be useful)

Upvotes: 2

Views: 1010

Answers (2)

Jindra Lacko
Jindra Lacko

Reputation: 8749

You can use orthographic projection in sf and ggplot2 projecting to "+proj=ortho" coordinate reference system.

Making the oceans turn blue may take some tweaking; I have resorted to buffering the Null Island by the Earth radius (inspired by this gist).

For more information of the arguments (i.e. lat_0 & lon_0) used have a look at the PROJ documentation https://proj.org/operations/projections/ortho.html

For a more graphic example consider this piece of code:

library(sf)
library(giscoR) # for the countries dataset only
library(ggplot2)

# projection string used for the polygons & ocean background
crs_string <- "+proj=ortho +lon_0=30 +lat_0=30"

# background for the globe - center buffered by earth radius
ocean <- st_point(x = c(0,0)) %>%
  st_buffer(dist = 6371000) %>%
  st_sfc(crs = crs_string)

# country polygons, cut to size
world <- gisco_countries %>% 
  st_intersection(ocean %>% st_transform(4326)) %>% # select visible area only
  st_transform(crs = crs_string) # reproject to ortho

# one of the visible ones red (don't really matter which one :)
world$fill_color <- ifelse(world$ISO3_CODE == "DEU", "interesting", "dull")
   
# now the action!
ggplot(data = world) +
  geom_sf(data = ocean, fill = "aliceblue", color = NA) + # background first
  geom_sf(aes(fill = fill_color), lwd = .1) + # now land over the oceans
  scale_fill_manual(values = c("interesting" = "red",
                               "dull" = "lightyellow"),
                    guide = "none") +
  theme_void()

ortographic view of world countries, with germany in red

Upvotes: 10

dieghernan
dieghernan

Reputation: 3412

That is amazing @jindra-lacko! I took the liberty of checking the code above by creating a polar view map of Antarctica (holy grial of maps ;)), and works amazingly!:

library(sf)
library(giscoR) # for the countries dataset only
library(ggplot2)

# Test of https://stackoverflow.com/a/70756593/7877917

# projection string used for the polygons & ocean background
crs_string <- "+proj=ortho +lat_0=-90 +lon_0=0"

# background for the globe - center buffered by earth diameter
ocean <- st_point(x = c(0, 0)) %>%
  st_buffer(dist = 6371000) %>%
  st_sfc(crs = crs_string)

# country polygons, cut to size
world <- gisco_countries %>%
  st_intersection(ocean %>% st_transform(4326)) %>% # select visible area only
  st_transform(crs = crs_string) # reproject to ortho

# one of the visible ones red (don't really matter which one :)
world$fill_color <- ifelse(world$ISO3_CODE == "DEU", "interesting", "dull")

# background for the globe - center buffered by earth diameter
ocean <- st_point(x = c(0, 0)) %>%
  st_buffer(dist = 6371000) %>%
  st_sfc(crs = crs_string)

# now the action!
ggplot(data = world) +
  geom_sf(data = ocean, fill = "aliceblue", color = "black") + # background first
  geom_sf(aes(fill = fill_color), lwd = .1) + # now land over the oceans
  scale_fill_manual(
    values = c(
      "interesting" = "red",
      "dull" = "lightyellow"
    ),
    guide = "none"
  ) +
  theme_void() +
  labs(
    title = "Polar View: Antarctica",
    caption = "Based on Jindra Lacko:\nhttps://stackoverflow.com/a/70756593/7877917"
  )

enter image description here

Upvotes: 2

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