initial_access_surface: Create the initial accessibility surface

In PATH-Global-Health/catchment: Weighted Spatial Point Catchment Modelling

Create the initial accessibility surface

Description

Create the initial accessibility surface

Usage

initial_access_surface(
  travel_matrix,
  transform = "inverse_dist_squared",
  minimum_time = 10,
  force_threshold = 300,
  n_fac_limit = NULL,
  normalized = TRUE,
  sparse = TRUE
)

Arguments

travel_matrix	A matrix containing travel times, which pixels indexed by rows and locations indexed by columns. Typically created with catchment::create_travel_matrix_from_folder().
transform	A character, numeric, or function. If character, a predefined transformation will be applied. Currently available options are "inverse_dist_squared". If numeric, then an inverse function with a defined value for the exponential term (e.g., 1/x^value). If a function, then the user-supplied transformation is applied.
minimum_time	A numeric used to defined a minimum travel time. Travel times below this value will be set to the minimum time, this helps prevent the initial probabilities from being overly skewed by small numbers.
force_threshold	A numeric used to define the maximum travel distance value, beyond which pixels will be forced to their nearest facility.
n_fac_limit	either NULL or integer >1 and less than number of facitiies. Used to set a limit on the number of possible facilities an individual picel can attend.
normalized	TRUE/FALSE Fix probabilities such that all rows (i.e., pixels) sum to 1.
sparse	TRUE/FALSE return a sparse matrix used by catchment_model

Value

A matrix. If sparse == FALSE, then N_pixel rows by N_locations matrix containing initial assess surface will be returned. If sparse == TRUE, then a "sparse" Matrix object, used by model_catchment, is returned.

PATH-Global-Health/catchment documentation built on Feb. 16, 2025, 12:39 a.m.