ggblend topography

gistfile1.R

library(metR)
library(data.table)
library(ggplot2)


proj <-  "+proj=lcc +lon_0=-60 +lat_1=-0 +lat_2=-40"

topo <- GetTopography(ConvertLongitude(-85),
                      330,  lat.north = 14, lat.south = -58, 
                      resolution = 2/60) |> 
  _[, c("dlon", "dlat") := Derivate(h ~ lon + lat)] |> 
  _[, c("dx", "dy") := list(dx(dlon, lat),
                            dy(dlat))] 


r <- 1/1.3
height <- 1600
png(filename = "~/Downloads/with_blend.png", width =  height*r, height = height)
with_blend <- topo |> 
  ggplot(aes(lon, lat)) +
  list(
    geom_raster(aes(fill = sqrt(dx^2 + dy^2)), alpha = 1),
    scale_fill_gradient(low = "white", high = "black", guide = "none"),
    ggnewscale::new_scale_fill(),
    geom_raster(data = \(x) subset(x, h> 0), aes(fill = h),alpha = 1),
    scale_fill_gradientn(colors = terrain.colors(5), guide = "none"),
    ggnewscale::new_scale_fill(),
    
    geom_raster(data = \(x) subset(x, h < 0), aes(fill = h), alpha = 1),
    scale_fill_gradientn(colors = topo.colors(10)[1:4], guide = "none"),
    ggnewscale::new_scale_fill()
    
  ) |> ggblend::blend("multiply") +
  
  geom_contour2(aes(z = h), breaks = 0) +
  coord_sf(crs = proj)  +
  theme_void() 
print(last_plot())

dev.off()

png(filename = "~/Downloads/no_blend.png", width =  height*r, height = height)
no_blend <- topo |> 
  ggplot(aes(lon, lat)) +
  list( 
    geom_raster(data = \(x) subset(x, h> 0), aes(fill = h),alpha = 1),
    scale_fill_gradientn(colors = terrain.colors(5), guide = "none"),
    ggnewscale::new_scale_fill(),
    
    geom_raster(data = \(x) subset(x, h < 0), aes(fill = h), alpha = 1),
    scale_fill_gradientn(colors = topo.colors(10)[1:4], guide = "none"),
    ggnewscale::new_scale_fill()
    
  ) |> ggblend::blend("multiply") +
  
  geom_contour2(aes(z = h), breaks = 0) +
  coord_sf(crs = proj)  +
  theme_void() 
print(last_plot())
dev.off()