plot(c(-180, 180), c(-90, 90))
lonlat(raster::raster())
p <- raster::projectExtent(raster::raster(), "+proj=igh")
lonlat(p, add = FALSE)
lonlat(p, levels = seq(-180, 180, by =15), add = FALSE)
lonlat(p, levels = seq(-180, 180, by = 5), add = FALSE, lon = TRUE)
lonlat(p, levels = seq(-180, 180, by = 15), add = TRUE, lat = TRUE)
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