Bring a Classified Map onto a Template Grid as a Mask and a Fraction

For a crop or land cover map at any resolution, gives the fraction of each template cell that belongs to the requested class or classes, and a mask of the cells where that fraction reaches min_fraction.

Usage

wapor_harmonize_mask(
  crop_map,
  template,
  class,
  min_fraction = 0.5,
  value = NULL,
  return_fraction = TRUE
)

Arguments

crop_map: Classified SpatRaster (class codes).
template: SpatRaster whose grid the result gets.
class: Class code or codes to keep.
min_fraction: Smallest fraction of a template cell that must belong to the class for the cell to enter the mask. Default 0.5, a majority rule (a heuristic, not a published threshold; choose it for your map).
value: Value of mask cells. Default NULL: 1 for one class, the code of the winning class for several.
return_fraction: Logical. Return the fraction as well. Default TRUE.

Value

With return_fraction = TRUE a list with mask (layer crop_mask, NA outside) and fraction (layer fraction, 0 to 1); otherwise the mask.

Details

Each class is turned into a 0/1 raster (cells of another class and cells without data are 0) and averaged onto the template grid. With several classes the class with the largest fraction wins the cell, ties go to the first class given, and fraction holds the winner's fraction.

The fraction is the recommended weights input of wapor_zonal_stats() at Level 1 and Level 2.

Examples

map <- terra::rast(nrows = 2, ncols = 2, xmin = 0, xmax = 20, ymin = 0, ymax = 20,
                   crs = "EPSG:32636", vals = c(1, 1, 1, 2))
cell <- terra::rast(nrows = 1, ncols = 1, xmin = 0, xmax = 20, ymin = 0, ymax = 20,
                    crs = "EPSG:32636")
terra::values(wapor_harmonize_mask(map, cell, class = 1)$fraction)
#>      fraction
#> [1,]     0.75