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Keep only patches connected to anchor features

Source: R/fl_patch_conn.R
fl_patch_conn.Rd

Identifies connected patches of 1-valued cells and keeps only those that overlap with anchor features (e.g., stream cells). Disconnected patches are set to 0.

Usage

fl_patch_conn(x, anchor, directions = 4L)

Arguments

x

A SpatRaster with binary values (0/1).

anchor

A SpatRaster identifying anchor cells. Any non-NA, non-zero cell is an anchor (e.g., rasterized streams).

directions

Integer. 4 for rook connectivity, 8 for queen. Default 4.

Value

A SpatRaster with the same grid as x. Only patches touching at least one anchor cell are retained.

Examples

dem <- terra::rast(system.file("testdata/dem.tif", package = "flooded"))
slope <- terra::rast(system.file("testdata/slope.tif", package = "flooded"))
streams <- sf::st_read(
  system.file("testdata/streams.gpkg", package = "flooded"),
  quiet = TRUE
)
stream_r <- fl_stream_rasterize(streams, dem, field = "upstream_area_ha")
gentle <- fl_mask(slope, threshold = 9, operator = "<=")

# Keep only gentle-slope patches that touch a stream
connected <- fl_patch_conn(gentle, stream_r)
terra::plot(connected, col = c("grey90", "darkgreen"),
     main = "Gentle slopes connected to streams")