Compute median from a SpatRaster using its GDAL PAM side-car histogram

Extracts the histogram stored in the GDAL PAM side-car XML file (e.g. raster.tif.aux.xml) and computes the exact median value by finding the bucket midpoint where the cumulative count reaches 50%.

Utilisation

median_from_rast(r)

Arguments

r

A SpatRaster (from terra) whose underlying file has a GDAL PAM side-car XML (e.g. raster.tif.aux.xml).

Valeur de retour

A single numeric value: the median of the raster (bucket midpoint).

Détails

Before running this function, you must generate the histogram side‑car: in a terminal, run:

gdalinfo -hist /path/to/your.tif

This computes and stores the histogram in /path/to/your.tif.aux.xml. Once the side-car exists, calling this function reads the stored <Histogram> data without re-scanning pixel values and returns the exact median bucket midpoint.

Exemples

if (FALSE) { # \dontrun{
library(terra)
r <- rast("eii_2023.tif")
# First, in the shell:
#   gdalinfo -hist eii_2023.tif
med <- median_from_rast(r)
} # }