Vectorize transition raster into individual change patches

Convert a transition SpatRaster (from dft_rast_transition()) into sf polygons — one row per connected patch of pixels sharing the same transition type. Useful for QA in GIS, spatial attribution to management zones, and patch-level reporting.

Usage

dft_transition_vectors(x, zones = NULL, zone_col = NULL, patch_area_min = NULL)

Arguments

x: A factor SpatRaster from dft_rast_transition() (the $raster element). Must have a projected CRS.
zones: Optional sf polygon layer for spatial attribution. Any partitioning: sub-basins, parcels, climate regions, management units.
zone_col: Character. Column name in zones identifying each zone. Required when zones is supplied.
patch_area_min: Numeric or NULL. Minimum patch area in m². Patches smaller than this are dropped before returning. NULL (default) keeps all.

Value

An sf data frame (polygon geometry) with columns:

patch_id (integer) — connected component ID
transition (character) — transition label (e.g. "Trees -> Rangeland")
area_ha (numeric) — patch area in hectares
Zone column (if zones supplied) — from spatial intersection

Examples

r17 <- terra::rast(system.file("extdata", "example_2017.tif", package = "drift"))
r20 <- terra::rast(system.file("extdata", "example_2020.tif", package = "drift"))
classified <- dft_rast_classify(list("2017" = r17, "2020" = r20), source = "io-lulc")
result <- dft_rast_transition(classified, from = "2017", to = "2020")

# Vectorize all transition patches
patches <- dft_transition_vectors(result$raster)
head(patches)
#> Simple feature collection with 6 features and 3 fields
#> Geometry type: GEOMETRY
#> Dimension:     XY
#> Bounding box:  xmin: 683391.9 ymin: 6029786 xmax: 686631.9 ymax: 6030196
#> Projected CRS: WGS 84 / UTM zone 9N
#>   patch_id         transition area_ha                       geometry
#> 1        1     Water -> Water    5.91 POLYGON ((686221.9 6030196,...
#> 2        2     Water -> Water    3.49 POLYGON ((683391.9 6030126,...
#> 3        3 Water -> Rangeland    0.01 POLYGON ((686441.9 6030106,...
#> 4        4     Trees -> Water    0.02 POLYGON ((686151.9 6030186,...
#> 5        5     Trees -> Water    0.35 MULTIPOLYGON (((686441.9 60...
#> 6        6     Trees -> Water    0.01 POLYGON ((683401.9 6030136,...

# Filter to large patches only
patches_large <- dft_transition_vectors(result$raster, patch_area_min = 1000)
head(patches_large)
#> Simple feature collection with 6 features and 3 fields
#> Geometry type: GEOMETRY
#> Dimension:     XY
#> Bounding box:  xmin: 683391.9 ymin: 6029066 xmax: 686631.9 ymax: 6030576
#> Projected CRS: WGS 84 / UTM zone 9N
#>    patch_id     transition area_ha                       geometry
#> 1         1 Water -> Water    5.91 POLYGON ((686221.9 6030196,...
#> 2         2 Water -> Water    3.49 POLYGON ((683391.9 6030126,...
#> 5         5 Trees -> Water    0.35 MULTIPOLYGON (((686441.9 60...
#> 11       11 Trees -> Water    0.28 POLYGON ((683591.9 6030026,...
#> 13       13 Trees -> Water    0.12 POLYGON ((686511.9 6029836,...
#> 15       15 Trees -> Trees   24.46 MULTIPOLYGON (((685251.9 60...