Topographic Wetness Index (W3) — indicator_water

Calculates TWI using fasterRaster/GRASS GIS (preferred) or terra fallback (D8). Higher values indicate areas with greater water accumulation potential.

Usage

indicator_water_twi(
  units,
  layers,
  dem_layer = "dem",
  method = c("auto", "grass", "d8")
)

Arguments

units: nemeton_units object
layers: nemeton_layers object containing DEM raster
dem_layer: Character. Name of DEM layer in layers object
method: Character. TWI calculation method: "auto" (prefer GRASS), "grass" (fasterRaster/GRASS GIS), or "d8" (terra D8). Default "auto".

Value

Numeric vector of TWI mean values

Details

The GRASS method (via fasterRaster) performs proper hydrological conditioning: depression filling, flow direction, flow accumulation, then TWI = ln(SCA / tan(slope)). The terra D8 method is a simpler approximation used as fallback.

Examples

if (FALSE) { # \dontrun{
layers <- nemeton_layers(rasters = list(dem = "dem_25m.tif"))
results <- indicator_water_twi(units, layers, dem_layer = "dem")
} # }