Skip to contents

Prepare separate tsunami zones for escape analysis and visualization

Source: R/tsunami_zones.R
prepare_tsunami_zones.Rd

Tsunami evacuation workflows often need two different zone objects. The land-only inundation zone is the area where road origins and output time surfaces should be mapped. The escape-boundary zone should combine the land-only inundation zone with water so that the coastline is not treated as an artificial escape boundary. This prevents false escape/safety points along the water-land edge when roads touch or approach the shoreline.

Usage

prepare_tsunami_zones(
  inundation,
  dem,
  target_crs = NULL,
  inundation_threshold = 0,
  land_threshold = 0,
  water_threshold = 0,
  dem_sign_multiplier = 1,
  resample_method = "bilinear",
  as_polygon = TRUE,
  dissolve = TRUE
)

Arguments

inundation

Inundation-depth raster or path to a raster. Cells greater than inundation_threshold are treated as inundated.

dem

Elevation/topobathymetry raster or path to a raster.

target_crs

Optional projected CRS in meters for returned objects.

inundation_threshold

Numeric threshold used to define inundated cells.

land_threshold

Numeric DEM threshold used to define land. Default is 0, so land is dem > 0 after applying dem_sign_multiplier.

water_threshold

Numeric DEM threshold used to define water. Default is 0, so water is dem < 0 after applying dem_sign_multiplier.

dem_sign_multiplier

Multiplier applied to the DEM before land/water classification. Use -1 when the DEM sign convention is reversed.

resample_method

Method passed to terra::resample() when aligning the inundation raster to the DEM. Use "bilinear" for depth rasters and "near" for categorical rasters.

as_polygon

Logical. If TRUE, return polygon zones in addition to rasters.

dissolve

Logical. Dissolve polygon pieces.

Value

A named list with land-only hazard_zone, water-combined escape_zone, and supporting rasters. hazard_zone should usually be used for origin generation, mapping, and output clipping. escape_zone should usually be passed to run_evacpath(escape_zone = ...) or find_escape_points().

Examples

dem <- terra::rast(nrows = 6, ncols = 6, xmin = 0, xmax = 6, ymin = 0, ymax = 6,
  crs = "EPSG:3857")
xy <- terra::crds(dem, df = TRUE)
terra::values(dem) <- -1.5 + 0.7 * xy$x + 0.2 * sin(xy$y)
inundation <- dem
terra::values(inundation) <- ifelse(terra::values(dem) > 0 & terra::values(dem) < 2.5, 1, 0)
zones <- prepare_tsunami_zones(inundation, dem, as_polygon = TRUE)
names(zones)
#> [1] "hazard_raster"      "escape_raster"      "land_mask"         
#> [4] "water_mask"         "inundation_aligned" "dem"               
#> [7] "hazard_zone"        "escape_zone"