如何将含NDVI值的投影栅格转为保留网格结构的CSV/Excel

If you need to export your NDVI raster into a grid-style CSV where the first row contains metric longitude (x) values, first column contains metric latitude (y) values, and cells hold the corresponding NDVI values, here's a straightforward approach using R's tidyverse tools:

Step 1: Load Required Libraries #

We'll use the raster package for handling raster data and tidyr (part of the tidyverse) to reshape the data from long to wide format.

library(raster)
library(tidyr)

Step 2: Prepare Your Raster (or Load Existing) #

Using your example raster for demonstration:

# Create sample raster (replace with your actual raster)
r <- raster(ncol=10, nrow=10)
values(r) <- 1:ncell(r)

# Convert to long-format data frame with coordinates
df <- as.data.frame(r, xy = TRUE)

Step 3: Reshape to Wide (Grid) Format #

We'll use pivot_wider to turn x-values into columns and keep y-values as rows. We also reorder the rows so the highest latitude (top of the raster) appears first in the CSV:

# Pivot to grid format
grid_df <- df %>%
  pivot_wider(names_from = x, values_from = layer) %>%
  arrange(desc(y))  # Reverse y order to match raster's top-to-bottom layout

Step 4: Export to CSV #

Finally, write the grid data frame to a CSV file. Setting row.names = FALSE ensures we don't add extra row numbers:

write.csv(grid_df, "ndvi_grid.csv", row.names = FALSE)

What the Output Looks Like #

For your sample raster, the resulting CSV will have:

• First column: y-values (from 81 down to -81)
• Column headers: x-values (-162, -126, ..., 162)
• Cells: Corresponding raster values (1-10 in the first row, 11-20 in the second, etc.)

Alternative with reshape2 #

If you prefer using reshape2 instead of tidyr, you can use dcast:

library(reshape2)
grid_df <- dcast(df, y ~ x, value.var = "layer")
grid_df <- grid_df[order(-grid_df$y), ]  # Reorder rows to match raster layout
write.csv(grid_df, "ndvi_grid.csv", row.names = FALSE)

This approach maintains the spatial grid structure of your raster, making it easy to map back to the original geographic coordinates in spreadsheet tools.

内容的提问来源于stack exchange，提问作者il nibbio