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Compute zonal statistics for a panel of rasters

Source: R/extract.R
extract_panel.Rd

Takes a named list of SpatRaster objects (one per year, as returned by ntl_download() or bhuvan_raster()) and an sf or SpatVector polygon layer, and returns a tidy long-format data frame with one row per region per year.

Usage

extract_panel(rasters, polygons, fun = "mean", id_col = NULL)

Arguments

rasters

A named list of SpatRaster objects. Names should be years (e.g., "2020", "2021"). Returned by ntl_download() or bhuvan_raster().

polygons

An sf object or SpatVector containing the regions to summarise over.

fun

Aggregation function name passed to terra::zonal(). Default "mean". Also accepts "sum", "median", etc.

id_col

Name of the column in polygons to use as region_id. If NULL (default), the first character column is used.

Value

A data frame with columns:

region_id

Character. Region identifier from polygons.

year

Integer. Year, taken from the name of each raster.

mean_radiance

Numeric. Aggregated radiance value.

n_pixels

Integer. Number of non-NA cells contributing to the stat.

Details

The polygons argument accepts any sf object – GADM, bharatviz GeoJSONs, LGD districts, or any shapefile loaded with sf::read_sf().

Examples

if (FALSE) { # \dontrun{
districts <- sf::read_sf("https://bharatviz.org/India-bhuvan-districts.geojson")
rasters <- bhuvan_raster(districts, years = 2018:2023)
panel <- extract_panel(rasters, districts)
head(panel)
} # }