在R中的ggplot2中的地图上覆盖栅格图层？

Question

我正在尝试将栅格图层叠加到ggplot中的地图上。栅格图层包含来自卫星标签的每个时间点的似然面。我还想在栅格图层上设置累积概率（95％，75％，50％）。

我已经弄清楚了如何在ggplot地图上显示栅格图层，但是坐标彼此不对齐。我尝试使每个投影都具有相同的投影，但似乎无法正常工作……我希望它们都适合我模型的边界（xmin = 149，xmax = 154，ymin = -14，ymax = -8.75

随附我的r代码和图形结果：

#load data
ncname <- "152724-13-GPE3"
ncfname <- paste(ncname, ".nc", sep = "")
ncin <- nc_open(ncfname)

StackedObject<-stack("152724-13-GPE3.nc", varname = "monthly_residency_distributions")
MergedObject<-overlay(StackedObject,fun=mean ) 
MergedObject[is.na(MergedObject)]<-0 
Boundaries<-extent(c(149, 154, -14, -8.75)) 
ExtendedObject<-extend(MergedObject, Boundaries) 
Raster.big<-raster(ncol=1200,nrow=900,ext=Boundaries) 
Raster.HR<-resample(x=ExtendedObject, y=Raster.big, method="bilinear") 
Raster.HR@data@values<- Raster.HR@data@values/sum(Raster.HR@data@values) 
RasterVals<-sort(Raster.HR@data@values)
Raster.breaks <- c(RasterVals[max(which(cumsum(RasterVals)<= 0.05 ))], RasterVals[max(which(cumsum(RasterVals)<= 0.25 ))], RasterVals[max(which(cumsum(RasterVals)<= 0.50 ))], 1)
Raster.cols<-colorRampPalette(c("yellow","orange","red"))
RasterCols<- c(Raster.cols(3))

#Create Map
shape2 <- readOGR(dsn = "/Users/shannonmurphy/Desktop/PNG_adm/PNG_adm1.shp", layer = "PNG_adm1")
map<- crop(shape2, extent(149, 154, -14, -8.75))
projection(map)<- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs")

p <- ggplot() + geom_polygon(data = map, aes(x = long, y = lat, group = group), color = "black", size = 0.25) + coord_map()

projection(Raster.HR)<- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs")

#plot raster and ggplot 

par(mfrow=c(1,1))
plot(p)
par(mfrow=c(1,1), new = TRUE)
plot(Raster.HR, col=RasterCols, breaks=Raster.breaks, legend = NULL, bbox(map)) 

请让我知道我是否应该使用另一个软件包/代码行来执行此操作！感谢任何帮助

Answer 1

好，我懂了。您想在ggplot上绘制多个栅格图层，或者希望栅格对象位于背景多边形对象上方。问题rasterVis::gplot在于它直接绘制栅格，不允许在上方或下方添加另一个栅格。您提醒我，我已经有了此需求，并修改了功能gplot来检索数据作为小标题，以便您可以随心所欲地使用它dplyr，然后再使用ggplot2。感谢您的提醒，我将其添加到当前的github库中供以后使用！
让我们使用一个可重现的示例来显示此功能：

创建数据集

• 创建世界Raster地图作为背景栅格地图
• 创建数据栅格，这里是到点的距离（限制为最大距离）

代码：

library(raster)

# Get world map
library(maptools)
data(wrld_simpl)
# Transform World as raster
r <- raster(wrld_simpl, res = 1)
wrld_r <- rasterize(wrld_simpl, r)

# Lets create a raster of data
pt1 <- matrix(c(100,0), ncol = 2)
dist1 <- distanceFromPoints(r, pt1)
values(dist1)[values(dist1) > 5e6] <- NA
plot(dist1)

# Plot both
plot(wrld_r, col = "grey")
plot(dist1, add = TRUE)

提取（部分）栅格值并转换为小标题的功能

#' Transform raster as data.frame to be later used with ggplot
#' Modified from rasterVis::gplot
#'
#' @param x A Raster* object
#' @param maxpixels Maximum number of pixels to use
#'
#' @details rasterVis::gplot is nice to plot a raster in a ggplot but
#' if you want to plot different rasters on the same plot, you are stuck.
#' If you want to add other information or transform your raster as a
#' category raster, you can not do it. With `SDMSelect::gplot_data`, you retrieve your
#' raster as a tibble that can be modified as wanted using `dplyr` and
#' then plot in `ggplot` using `geom_tile`.
#' If Raster has levels, they will be joined to the final tibble.
#'
#' @export

gplot_data <- function(x, maxpixels = 50000)  {
  x <- raster::sampleRegular(x, maxpixels, asRaster = TRUE)
  coords <- raster::xyFromCell(x, seq_len(raster::ncell(x)))
  ## Extract values
  dat <- utils::stack(as.data.frame(raster::getValues(x))) 
  names(dat) <- c('value', 'variable')

  dat <- dplyr::as.tbl(data.frame(coords, dat))

  if (!is.null(levels(x))) {
    dat <- dplyr::left_join(dat, levels(x)[[1]], 
                            by = c("value" = "ID"))
  }
  dat
}

在ggplot中绘制多个栅格

您可以gplot_data用来将任何栅格转换为小标题。然后，您可以添加使用任何修改dplyr的情节和ggplot有geom_tile。有趣的一点是geom_tile，只要该fill选项具有可比性，您就可以根据需要使用任意多个时间。否则，您可以使用以下技巧NA在背景栅格地图中删除值并使用唯一的fill颜色。

# With gplot_data
library(ggplot2)

# Transform rasters as data frame 
gplot_wrld_r <- gplot_data(wrld_r)
gplot_dist1 <- gplot_data(dist1)

# To define a unique fill colour for the world map,
# you need to remove NA values in gplot_wrld_r which 
# can be done with dplyr::filter
ggplot() +
  geom_tile(data = dplyr::filter(gplot_wrld_r, !is.na(value)), 
            aes(x = x, y = y), fill = "grey20") +
  geom_tile(data = gplot_dist1, 
            aes(x = x, y = y, fill = value)) +
  scale_fill_gradient("Distance",
                      low = 'yellow', high = 'blue',
                      na.value = NA) +
  coord_quickmap()

在多边形上绘制栅格

当然，将背景图作为多边形对象，此技巧还可以让您在其上添加栅格：

wrld_simpl_sf <- sf::st_as_sf(wrld_simpl)

ggplot() +
  geom_sf(data = wrld_simpl_sf, fill = "grey20",
          colour = "white", size = 0.2) +
  geom_tile(data = gplot_dist1, 
            aes(x = x, y = y, fill = value)) +
  scale_fill_gradient("Distance",
                      low = 'yellow', high = 'blue',
                      na.value = NA)

编辑：gplot_data现在在这个简单的R包中：https : //github.com/statnmap/cartomisc