在 R 中重新投影时停止映射

Question

我想显示一张没有格林威治作为子午线的地图。例如，经度为 130。当我这样做时，地图会在显示屏上向后“环绕”。

在这种情况下，南美洲的部分地区在地图上被拉回 - 两极的部分也是如此。

我使用的代码是：

library("ggplot2")
theme_set(theme_bw())
library("sf")
library("rnaturalearth")
library("rnaturalearthdata")
world <- ne_countries(scale = "medium", returnclass = "sf")

ggplot(data = world) +
    geom_sf() +
    coord_sf(crs = "+proj=cea +lon_0=130 +x_0=0 +y_0=0 +lat_ts=45 +ellps=WGS84 +datum=WGS84 +units=m +no_defs")

如果南美洲东部出现在地图左侧，我很高兴 - 我只是不希望它覆盖地图。我能做些什么来防止这种奇怪的图形故障？

Answer 1

在此处查看有关如何实现该目标的完整表述。步骤是：

1. 获取数据并使用st_make_valid 使其有效（如果您使用sf (>= 1.0.0) ，则需要
2. 创建一个细长的多边形，根据您想要的经度，多边形会折断。
3. 从您的形状中删除创建的多边形。这将有效地“打破”正确位置上的多边形（即投影后地图的新限制）。
4. 转换为您想要的投影和地图。

在这里查看完整的reprex：

# Load libraries
library(ggplot2)
theme_set(theme_bw())

library(sf)
#> Linking to GEOS 3.9.0, GDAL 3.2.1, PROJ 7.2.1
library(rnaturalearth)
library(rnaturalearthdata)
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union



# Set target crs

target_crs <- st_crs("+proj=cea +lon_0=130 +x_0=0 +y_0=0 +lat_ts=45 +ellps=WGS84 +datum=WGS84 +units=m +no_defs")


# Get data and transform to lon/lat 4326
world <- ne_countries(scale = "medium", returnclass = "sf") %>%
  st_transform(4326) %>%
  st_make_valid()


# define a long & slim polygon that overlaps the meridian line & set its CRS to match
# that of world

# Centered in lon 130 on this example

offset <- 180 - 130


polygon <- st_polygon(x = list(rbind(
  c(-0.0001 - offset, 90),
  c(0 - offset, 90),
  c(0 - offset, -90),
  c(-0.0001 - offset, -90),
  c(-0.0001 - offset, 90)
))) %>%
  st_sfc() %>%
  st_set_crs(4326)

# Remove slim polygon
world_fixed <- world %>% st_difference(polygon)
#> Warning: attribute variables are assumed to be spatially constant throughout all
#> geometries

# Transform to desired projection

world_fixed <- st_transform(world_fixed, target_crs)


# Plot - no need ggplot2::coord_sf()

ggplot(data = world_fixed) +
  geom_sf()

sessionInfo()
#> R version 4.1.0 (2021-05-18)
#> Platform: x86_64-w64-mingw32/x64 (64-bit)
#> Running under: Windows 10 x64 (build 19042)
#> 
#> Matrix products: default
#> 
#> locale:
#> [1] LC_COLLATE=Spanish_Spain.1252  LC_CTYPE=Spanish_Spain.1252   
#> [3] LC_MONETARY=Spanish_Spain.1252 LC_NUMERIC=C                  
#> [5] LC_TIME=Spanish_Spain.1252    
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] dplyr_1.0.7             rnaturalearthdata_0.1.0 rnaturalearth_0.1.0    
#> [4] sf_1.0-1                ggplot2_3.3.5          
#> 
#> loaded via a namespace (and not attached):
#>  [1] Rcpp_1.0.7         pillar_1.6.1       compiler_4.1.0     highr_0.9         
#>  [5] class_7.3-19       tools_4.1.0        digest_0.6.27      lattice_0.20-44   
#>  [9] evaluate_0.14      lifecycle_1.0.0    tibble_3.1.3       gtable_0.3.0      
#> [13] pkgconfig_2.0.3    rlang_0.4.11       reprex_2.0.0       DBI_1.1.1         
#> [17] yaml_2.2.1         xfun_0.24          e1071_1.7-7        s2_1.0.6          
#> [21] withr_2.4.2        styler_1.5.1       stringr_1.4.0      knitr_1.33        
#> [25] rgeos_0.5-5        generics_0.1.0     fs_1.5.0           vctrs_0.3.8       
#> [29] classInt_0.4-3     grid_4.1.0         tidyselect_1.1.1   glue_1.4.2        
#> [33] R6_2.5.0           fansi_0.5.0        rmarkdown_2.9      sp_1.4-5          
#> [37] purrr_0.3.4        magrittr_2.0.1     units_0.7-2        backports_1.2.1   
#> [41] scales_1.1.1       ellipsis_0.3.2     htmltools_0.5.1.1  assertthat_0.2.1  
#> [45] colorspace_2.0-2   KernSmooth_2.23-20 utf8_1.2.2         proxy_0.4-26      
#> [49] stringi_1.7.3      wk_0.5.0           munsell_0.5.0      crayon_1.4.1

^{由reprex package (v2.0.0) 于 2021-07-27 创建}