如何用栅格数据拉直倾斜的 ggplot2 地图？

Question

在绘制我的 NLCD 树冠数据（栅格）地图时，地图不是直的或与地图边界对齐。使用 projectRaster 函数时似乎会出现偏斜。有没有办法将光栅调整为水平甚至与边界？当运行下面的代码/查看上传的图像时，我想删除的偏斜是深灰色的不均匀边框，同时让树数据填充整个帧。我一直无法找到任何解决方案，所以我很感激任何建议！

图片歪斜：1

library(sf)
#devtools::install_github("ropensci/FedData")
library(FedData)
library(ggplot2)
library(raster)
library(RColorBrewer)

ext <- extent(734666.5, 795961.6, 4017870, 4053632)

extent <- polygon_from_extent(raster::extent(ext), proj4string='+proj=utm +datum=NAD83 +zone=16N')

WMAtc <- get_nlcd(template = polygon_from_extent(ext, (proj4string = "+proj=utm +zone=16N ellps+NAD83")), year = 2016, dataset = "Tree_Canopy", label = "Can", force.redo = T) 

WMAtc_projected <- projectRaster(WMAtc, crs = "+proj=utm +zone=16N +datum=NAD83") 

tc_df <- as.data.frame(WMAtc_projected, xy=TRUE) 

ggplot() + 
  geom_raster(data = tc_df, aes(x = x, y = y, fill=tc_df[,3])) +
  scale_fill_gradientn(colors = brewer.pal(8, "Greens"), name = "Tree Canopy Cover")

Answer 1

一位教授慷慨地帮助我解决了这个问题。使用他的代码，您可以看到范围边界框与下载的 NLCD 数据相关的位置。投影时，NLCD 数据会调整并扩展到原始范围之外。要解决此问题，您可以裁剪额外的数据，它会重新对齐地图的图像。

library(FedData)
library(ggplot2)
library(raster)
library(RColorBrewer)
library(sf)

ext <- extent(734666.5, 795961.6, 4017870, 4053632)

extent <- polygon_from_extent(raster::extent(ext), proj4string='+proj=utm +datum=NAD83 +zone=16N')

WMAtc <- get_nlcd(template = polygon_from_extent(ext, (proj4string = "+proj=utm +zone=16N ellps+NAD83")),year = 2016, dataset = "Tree_Canopy", label = "Can")

WMAtc_projected <- projectRaster(WMAtc, crs = "+proj=utm +zone=16N +datum=NAD83")

tc_df <- as.data.frame(WMAtc_projected, xy=TRUE)

ggplot() +
  geom_raster(data = tc_df, aes(x = x, y = y, fill=tc_df[,3])) +
  scale_fill_gradientn(colors = brewer.pal(8, "Greens"), name = "Tree Canopy Cover") +
  geom_sf(data=st_as_sf(extent), fill=NA, col="red") # show desired raster extent

WMAtc_projected_cropped = crop(WMAtc_projected, extent) #crop to remove extra bits
tc_df_cropped <- as.data.frame(WMAtc_projected_cropped, xy=TRUE)

ggplot() +
  geom_raster(data = tc_df_cropped, aes(x = x, y = y, fill=tc_df_cropped[,3])) +
  scale_fill_gradientn(colors = brewer.pal(8, "Greens"), name = "Tree Canopy Cover") +
  geom_sf(data=st_as_sf(extent), fill=NA, col="red")