使用 terra 绘制光栅文件

Question

下面的代码可以很好地映射具有物种数据的栅格文件（25 m 空间分辨率）。

问题：我正在努力区分地图外的值（背景，也视为 0）和地图内的真实 0 值。

# Load required libraries
library(terra)          # for handling raster files

# Load the raster file
raster_data <- rast("pollinator.tif")

# Define categories and breaks
 breaks <- seq(0, 0.03, length.out = 6) # 5 categories, so 6 breaks
categorized_raster <- classify(raster_data, rcl = cbind(breaks[-length(breaks)], 
breaks[-1], 1:5))

# Handle background (outside map) values separately
background_value <- -1  # Assign a distinct value for the background
categorized_raster[is.na(values(categorized_raster))] <- background_value

# Define custom colors
 colors <- c("white", "#fde725", "#5ec962", "#21918c", "#3b528b", "#440154") # Add 
 white for background

# Adjust the color assignment to include the background
# "white" (background) is mapped to -1, followed by the defined category colors
 plot(categorized_raster, col = colors, main = "Pollinator Abundance (Andrena 
 strohmella, Spring)",
 xlab = "Longitude", ylab = "Latitude", axes = TRUE, legend = TRUE)

Answer 1

示例数据

library(terra)
r <- rast(system.file("ex/elev.tif", package="terra"))
x <- classify(r, 5) |> as.int()

显而易见的解决方案是不要使用“白色”作为数据的颜色

colors <- c("#fde725", "#5ec962", "#21918c", "#3b528b", "#440154") 
plot(x, col=colors)

但是如果这样做，您可以将背景 (

NA

) 颜色设置为其他颜色，在本例中为“浅灰色”。

colors <- c("white", "#fde725", "#5ec962", "#21918c", "#3b528b", "#440154") 
plot(x, col=colors, colNA="light gray")