si_calculate: Calculate flow using a pre-existing function

In Robinlovelace/si: Flexible Framework for Developing Spatial Interaction Models

Calculate flow using a pre-existing function

Description

Executes a spatial interaction model based on an OD data frame and user-specified function

Usage

si_calculate(
  od,
  fun,
  constraint_production,
  constraint_attraction,
  constraint_total,
  output_col = "interaction",
  ...
)

Arguments

od	A data frame representing origin-destination data, e.g. as created by si_to_od()
fun	A function that calculates the interaction (e.g. the number of trips) between each OD pair
constraint_production	Character representing column in od. This argument, when set, ensures that the outputs are 'production constrained': the total 'interaction' (e.g. n. trips) for all OD pairs is set such that the total for each zone of origin cannot go above this value.
constraint_attraction	Character representing column in od. This argument, when set, ensures that the outputs are 'attraction constrained': the total 'interaction' (e.g. n. trips) for all OD pairs is set such that the sum of trips to destination is equal to the mean value per destination.
constraint_total	Single number representing the total interaction. This argument, when set, ensures that the sum of the interaction calculated will equal the value given.
output_col	Character string containing the name of the new output column. "interaction" by default.
...	Arguments passed to fun

Value

An sf data frame

Examples

od = si_to_od(si_zones, si_zones, max_dist = 4000)
fun_dd = function(d = "distance_euclidean", beta = 0.3) exp(-beta * d / 1000)
fun_dd(d = (1:5) * 1000)
od_dd = si_calculate(od, fun = fun_dd, d = distance_euclidean)
plot(od$distance_euclidean, od_dd$interaction)
fun = function(O, n, d, beta) O * n * exp(-beta * d / 1000)
od_output = si_calculate(od, fun = fun, beta = 0.3, O = origin_all, 
  n = destination_all, d = distance_euclidean)
head(od_output)
plot(od$distance_euclidean, od_output$interaction)
od_pconst = si_calculate(od, fun = fun, beta = 0.3, O = origin_all,
  n = destination_all, d = distance_euclidean, constraint_production = origin_all)
# Origin totals in OD data should equal origin totals in zone data
library(dplyr)
origin_totals_zones = od_pconst |>
  group_by(geo_code = O) |>
  summarise(all_od = sum(interaction)) |>
  sf::st_drop_geometry()
zones_joined = left_join(si_zones, origin_totals_zones)
plot(zones_joined$all, zones_joined$all_od)
plot(od_pconst$distance_euclidean, od_pconst$interaction)
plot(od_pconst["interaction"], logz = TRUE)
od_dd = si_calculate(od, fun = fun_dd, d = distance_euclidean, output_col = "res")
head(od_dd$res)
od_dd = si_calculate(od, fun = fun_dd, d = distance_euclidean, constraint_total = 10)
sum(od_dd$interaction)

Robinlovelace/si documentation built on Sept. 28, 2024, 10:41 a.m.