如何在使用极线(epsg:3995)投影和ggspatial时在ggplot中的66度平行北线上绘制一条线

Question

我正试着在北纬66度上画一个蓝色圆圈。在我正在制作的地图上。

我通常fortify()一个SpatialPolygonsDataFrame，然后使用geom_polygon()、coord_map("ortho" , ylim = c(50, 90))和geom_hline()的组合来实现这一点。

然而，对于一个新的项目，我将不得不在一个已经有CRS日期的对象上使用ggspatial::layer_spatial()，因此这种直线绘制和自动重新投影不起作用。

这是我常用方法的演示，它是有效的：

library(tidyverse)

map_data <- rnaturalearth::ne_countries()
map_data_df <- fortify(map_data)

ggplot() + 
  geom_polygon(data = map_data_df, 
               aes(x = long,
                   y = lat,
                   group = group),
               col = "black",
               fill = "lightgrey") + 
  coord_map("ortho" , ylim = c(50, 90))  +
  geom_hline(yintercept = 66, col = "blue")

​

​

我试图在这段代码中复制它，但显然不起作用，因为geom_hline()没有正确的投影：

map_data_transformed <- sp::spTransform(map_data, sp::CRS("+init=epsg:3995"))
# needs some fixing to close all the polygons
map_data_transformed <- rgeos::gBuffer(map_data_transformed, byid=TRUE, width=0)


ggplot() + 
  ggspatial::layer_spatial(data = map_data_transformed, 
                           fill = "lightgrey", col = "black", size = .2)+
  coord_sf( xlim = c(-4500000 , 4500000),
            ylim = c(-4500000 , 4500000)) +
  geom_hline(yintercept = 66, col = "blue")

​

​

Answer 1

看看这对你有没有用？

# define parallel north line as a spatial polygon with latitude / longitude projection
new_line <- sp::Polygon(coords = matrix(c(seq(-180, 180),
                                          rep(66, times = 361)), # change this for other
                                                                 # intercept values
                                        ncol = 2))
new_line <- sp::SpatialPolygons(Srl = list(sp::Polygons(srl = list(new_line), 
                                                        ID = "new.line")),
                                proj4string = sp::CRS("+proj=longlat +datum=WGS84"))

# change projection to match that of data
new_line <- sp::spTransform(new_line, sp::CRS("+init=epsg:3995"))

# plot
ggplot() + 
  ggspatial::layer_spatial(data = map_data_transformed, 
                           fill = "lightgrey", col = "black", size = .2) +
  ggspatial::layer_spatial(data = new_line,
                           fill = NA, col = "blue") +
  coord_sf( xlim = c(-4500000 , 4500000),
            ylim = c(-4500000 , 4500000))

​

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