spin.R

library(libs2)

make_hemisphere <- function(lon = 0, detail = 100, epsilon = 1) {

  lat_values <- seq(90, -90, length.out = detail)

  coord_df <- unique(
    data.frame(
      lon = c(rep(lon - 90 + 1, detail), rep(lon + 90 - 1, detail)),
      lat = c(lat_values, rev(lat_values))
    )
  )

  coords <- paste0(coord_df$lon, " ", coord_df$lat, collapse = ", ")
  sprintf("POLYGON ((%s))", coords)
}

plot_hemisphere <- function(geog, lon = 0) {
  hemisphere <- s2geography(make_hemisphere(lon))
  geog_hemisphere <- s2_intersection(geog, hemisphere)
  geog_hemisphere_wkb <- wk::new_wk_wkb(s2_asbinary(geog_hemisphere))
  geog_hemisphere_coords <- wk::wkb_coords(geog_hemisphere_wkb, sep_na = TRUE)
  geog_hemisphere_proj <- mapproj::mapproject(
    geog_hemisphere_coords$x,
    geog_hemisphere_coords$y,
    projection = "orthographic",
    orientation = c(0, lon, 0)
  )

  withr::with_par(list(mai = c(0, 0, 0, 0), omi = c(0, 0, 0, 0)), {
    plot(
      double(), double(),
      xlim = c(-1, 1),
      ylim = c(-1, 1),
      asp = 1
    )

    polypath(geog_hemisphere_proj)
  })
}

countries <- s2data_countries()

ragg::agg_png()
for (x in seq(0, 360, length.out = 99)) {
  message(x)
  try(plot_hemisphere(countries, x))
}
dev.off()

gifski::gifski(list.files(pattern = "Rplot"), width = 480, height  = 480, loop = TRUE, delay = 1/25)