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Calculate Area Proportions for Categorical Raster Classes (Generic)

Source: R/extract_cat_raster.R
extract_cat_raster.Rd

Extracts and calculates the **area proportion** of each categorical class (e.g., LULC) found within each input polygon. This function uses area-weighting to ensure highly accurate, sub-pixel zonal statistics.

Usage

extract_cat_raster(spat_raster_cat, sf_hex_grid, proportion = TRUE)

Arguments

spat_raster_cat

A single-layer SpatRaster object containing categorical values.

sf_hex_grid

An sf object containing polygonal geometries. The function will use h3_address if present, otherwise it creates and uses a temporary ID column for joining.

proportion

Logical. If TRUE (default), the output values are the proportion of the polygon area covered by each category (summing to 1 for the covered area). If FALSE, the output is the raw sum of the coverage fraction (area).

Value

An sf object identical to sf_hex_grid, but with new columns appended for each categorical value found in the raster. Column names follow the pattern <layer_name>_prop_<category_value>. Columns are **numerically ordered** by the category value.

Details

This function replaces the simplistic, non-area-weighted table() counting method with a robust custom function utilizing dplyr and the coverage_fraction column from exactextractr. Key features include:

  • **Area-Weighted Accuracy:** Uses coverage_fraction for precise results.

  • **NA Filtering:** Excludes NA raster values to prevent a prop_NaN column.

  • **Numerical Ordering:** Sorts the final output columns by category number (e.g., 70 before 80).

Examples

if (FALSE) { # \dontrun{
# Assuming 'lulc' is a categorical SpatRaster and 'hex_grid' is an sf polygon grid
# cat_data_p <- extract_cat_raster(lulc, hex_grid)
# head(cat_data_p)
} # }