Spilhaus
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Day 26 of 30DayMapChallenge: « Map projections » (previously).
After seeing this post by Cédric Vidonne I had to try to use the Spilhaus projection too.
Config
library(dplyr)
library(ggplot2)
library(scales)
library(glue)
library(terra)
source("spilhaus.R") # from https://github.com/rtlemos/spilhaus/ see below
Data
Mass concentration of chlorophyll a in sea water. Get the current data from Copernicus: Global Ocean Biogeochemistry Analysis and Forecast (European Union-Copernicus Marine Service 2019). You’ll need to register first.
An API is available, but for this one shot a manual download is easier:
chlorophyll <- rast("cmems_mod_glo_bgc-pft_anfc_0.25deg_P1D-m_1732694885194.nc")
Reproject
Based on the functions made by Ricardo T. Lemos.
spilhaus_df <- make_spilhaus_xy_gridpoints(spilhaus_res = 1000) lonlat <- from_spilhaus_xy_to_lonlat(spilhaus_df$x, spilhaus_df$y) spilhaus_df$z <- pull(extract(chlorophyll, lonlat), 1) spilhaus_df$l <- is.na(spilhaus_df$z) pretty_spilhaus_df <- pretify_spilhaus_df(spilhaus_df)
Map
pretty_spilhaus_df |>
ggplot(aes(x, y, fill = z)) +
geom_raster() +
scale_fill_viridis_c(option = "viridis",
limits = c(0, .8),
na.value = viridis_pal()(2)[2],
name = bquote(atop("2024-11-28", "Chlorophyll a ("*mg %.% m^-3*")"))) +
coord_equal() +
labs(caption = glue("https://r.iresmi.net/ - {Sys.Date()}
Generated using E.U. Copernicus Marine Service Information 10.48670/moi-00015")) +
theme_void() +
theme(plot.background = element_rect(fill = "black",
color = "black"),
plot.caption = element_text(size = 6,
color = "darkgrey"),
legend.position = c(0.85, 0.85),
legend.title = element_text(color = "white"),
legend.text = element_text(color = "white"))
References
European Union-Copernicus Marine Service. 2019. “Global Ocean Biogeochemistry Analysis and Forecast.” Mercator Ocean International. https://doi.org/10.48670/MOI-00015.
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