makeCatchment: Generate catchment polygons for groups of locations

In andresgmejiar/lbmech: A Package to Study the Mechanics of Landscape and Behavior

Generate catchment polygons for groups of locations

Description

A function to perform the necessary raster arithmetic to determine the catchment of a location based on a movement cost function and an optional weight. getCosts must have been run before this tool can be used.

Usage

makeCatchment(
  rasters = tempdir(),
  cost,
  direction = "both",
  ids = NULL,
  name = NULL,
  w = NULL
)

Arguments

rasters	One of either a character string or multilayer SpatRaster. If character string, it represents the filepath to the workspace used as dir for the previous functions. Default is tempdir() but unless you are not following best practices you will have to change it to your output directory. If multilayer SpatRaster, it should be the output (or identical in form) to the getCosts function with "object" %in% output.
cost	A character with the desired pre-calculated cost names (e.g. 'dt' for time, 'dW_l' for work using energyCosts).
direction	A character vector containing one or both of c("in","out") or the singular string 'both'. This determines whether costs to or from the nodes are calculated.
ids	A character vector containing the IDs of the locations to consider in the catchment calculation. Default is ids = NULL, which considers all of the locations in the rasters multilayer SpatRaster or the name shapefile if rasters is a directory string.
name	A character string representing the outname in getCosts containing all of the locations of interest. Ignored if ids is provided or if rasters is a multilayer SpatRaster
w	A named numreic vector with multiplicative weights for a given location. Names must correspond with ID strings. Missing locations are assumed to have a weight of 1.

Details

See also mwVoronoi

Value

A SpatVector with catchment polygons

Examples

# Generate a DEM
n <- 5
dem <- expand.grid(list(x = 1:(n * 100),
                        y = 1:(n * 100))) / 100
dem <- as.data.table(dem)
dem[, z := 250 * exp(-(x - n/2)^2) + 
      250 * exp(-(y - n/2)^2)]
dem <- rast(dem)
ext(dem) <- c(10000, 20000, 30000, 40000)
crs(dem) <- "+proj=lcc +lat_1=48 +lat_2=33 +lon_0=-100 +datum=WGS84"

# Export it so it doesn't just exist on the memory
dir <- tempdir()
writeRaster(dem, paste0(dir,"/DEM.tif"),overwrite=TRUE)


# Import raster, get the grid
dem <- rast(paste0(dir,"/DEM.tif"))
grid <- makeGrid(dem = dem, nx = n, ny = n, sources = TRUE)

# Import the data lying between x = (12000,16000) and y = (32000,36000)
region <- ext(c(12000,16000,32000,36000))
region <- as.polygons(region)
crs(region) <- crs(grid)

# Generate five random points that fall within the region
points <- data.table(ID = 1:5,
                     x = runif(5, ext(region)[1], ext(region)[2]),
                     y = runif(5, ext(region)[3], ext(region)[4]))
                     
# Make a world but limit it to the DEM grid size
defineWorld(source = grid, cut_slope = 0.5, 
            res = res(dem), dir = dir, overwrite=TRUE)
            
# Calculate cost rasters
costRasters  <- getCosts(region, from = points, dir = dir,
                         destination = 'all',
                         polygons = 'center',
                         costs = 'all', costFUN = energyCosts,
                         output = c('object','file'),
                         m = 70, v_max = 1.5, BMR = 76, k = 3.5, s = 0.05, l_s = 1,
                         L = 0.8)
                         
# Calculate catchments for work
catchments <- makeCatchment(costRasters,
                            cost = 'dW_l')

andresgmejiar/lbmech documentation built on Feb. 2, 2025, 12:37 a.m.