Calculate the total edge length of a raster associated with each park polygon

Helper function within parks_calc_attributes(). The total edge length of (classified) raster patches contained within the polygons will be calculated. Additionally, the argument raster_edge_buffer provides a way include patches in close proximity to the polygons. The total edge lengths are summed together and appended to the polygons data as additional columns (or one column, if there is only one raster class). Note that this operation may take a while to complete, as it involves the conversion of rasters to polygons (and vice versa).

raster_edge_length(
  polygons,
  raster,
  raster_min_patch_size = units::set_units(0, "m^2"),
  raster_edge_buffer = units::set_units(0, "m^2"),
  relative = TRUE
)

Arguments

polygons: sf (with projected coordinate reference system).
raster: SpatRaster object from terra::rast(). Should have a (projected) coordinate reference system similar to polygons.
raster_min_patch_size: Minimum patch size to be included in results. Provided either as a units object (see units::set_units()), or a number in the units of the coordinate reference system. Defaults to 0 m^2.
raster_edge_buffer: numeric. Specify buffer distance to add to polygonised raster; the total edge length of polygons that intersect the buffered raster will be summed up together with the total edge length contained within the polygons. Defaults to 0 (only patches fully contained within polygons will be considered). Provided either as a units object (see units::set_units()), or a number in the units of the coordinate reference system.
relative: logical. Whether or not to calculate relative amounts (i.e. ratio of edge-to-perimeter length). Defaults to TRUE.

Value

polygons with added column(s) < class value >_length, and < class value >_length_perim_ratio if relative is set to TRUE. Note that the value 0 will be summarised; convert pixels to NA if you wish to exclude them.