面具海洋 - wrld_simpl

Question

我一直试图在下面的代码中将海洋涂成白色或透明，但到目前为止都没有成功。我在 Stack 上看到了其他帖子，但无法将它们应用到我的示例中（例如，我如何在美国地图中为海洋着色？）。我欢迎建议。非常感谢！

library(raster)
library(ggplot2)
library(maptools)
data("wrld_simpl")

#sample raster
r <- raster(ncol=10, nrow=20)
r[] <- 1:ncell(r)
extent(r) <- extent(c(-20, 20, -20, 20))

#plotting
var_df <- as.data.frame(rasterToPoints(r))
p <- ggplot() +
  geom_polygon(data = wrld_simpl[wrld_simpl@data$UN!="10",], 
               aes(x = long, y = lat, group = group),
               colour = "black", fill = "grey") # does the fortification automatically
p <- p + geom_raster(data = var_df, aes(x = x, y = y, fill = layer))
p <- p + coord_equal() +  theme_bw()  +labs(x="", y="") 
p <- p + theme(legend.key=element_blank(), 
               axis.text.y =element_text(size=16),
               axis.text.x =element_text(size=16),
               legend.text =element_text(size=12), 
               legend.title=element_text(size=12))
p <- p + scale_fill_gradientn(colours = rev(terrain.colors(10)))
p <- p + geom_polygon(data = wrld_simpl[wrld_simpl@data$UN!="10",], 
                      aes(x = long, y = lat, group = group), 
                      colour = "black", fill = NA) 
p

Answer 1

我对你的问题的解释是你想在陆地表面而不是在海洋上显示栅格。要做到这一点mask，陆地表面的栅格更容易，我首先分解栅格以使边缘更平滑：

#sample raster
r <- raster(ncol=10, nrow=20)
r[] <- 1:ncell(r)
extent(r) <- extent(c(-20, 20, -20, 20))

r=disaggregate(r,10)
r=mask(r,wrld_simpl)

#plotting
var_df <- as.data.frame(rasterToPoints(r))
p <- ggplot() +
  geom_polygon(data = wrld_simpl[wrld_simpl@data$UN!="10",], 
               aes(x = long, y = lat, group = group),
               colour = "black", fill = "grey") # does the fortification automatically
p <- p + geom_raster(data = var_df, aes(x = x, y = y, fill = layer))
p <- p + coord_equal() +  theme_bw()  +labs(x="", y="") 
p <- p + theme(legend.key=element_blank(), 
               axis.text.y =element_text(size=16),
               axis.text.x =element_text(size=16),
               legend.text =element_text(size=12), 
               legend.title=element_text(size=12))
p <- p + scale_fill_gradientn(colours = rev(terrain.colors(10)))
p <- p + geom_polygon(data = wrld_simpl[wrld_simpl@data$UN!="10",], 
                      aes(x = long, y = lat, group = group), 
                      colour = "black", fill = NA) 
p