dodgr (version 0.4.0)

dodgr_flows_si: Aggregate flows throughout a network using a spatial interaction model.

Description

Aggregate flows throughout a network using an exponential Spatial Interaction (SI) model between a specified set of origin and destination points, and associated vectors of densities.

Usage

dodgr_flows_si(
  graph,
  from,
  to,
  k = 500,
  dens_from = NULL,
  dens_to = NULL,
  contract = TRUE,
  norm_sums = TRUE,
  heap = "BHeap",
  tol = 0.000000000001,
  quiet = TRUE
)

Value

Modified version of graph with additional flow column added.

Arguments

graph

data.frame or equivalent object representing the network graph (see Details)

from

Vector or matrix of points from which aggregate flows are to be calculated (see Details)

to

Vector or matrix of points to which aggregate flows are to be calculated (see Details)

k

Width of exponential spatial interaction function (exp (-d / k)), in units of 'd', specified in one of 3 forms: (i) a single value; (ii) a vector of independent values for each origin point (with same length as 'from' points); or (iii) an equivalent matrix with each column holding values for each 'from' point, so 'nrow(k)==length(from)'. See Note.

dens_from

Vector of densities at origin ('from') points

dens_to

Vector of densities at destination ('to') points

contract

If TRUE (default), calculate flows on contracted graph before mapping them back on to the original full graph (recommended as this will generally be much faster). FALSE should only be used if the graph has already been contracted.

norm_sums

Standardise sums from all origin points, so sum of flows throughout entire network equals sum of densities from all origins (see Note).

heap

Type of heap to use in priority queue. Options include Fibonacci Heap (default; FHeap), Binary Heap (BHeap), Trinomial Heap (TriHeap), Extended Trinomial Heap (TriHeapExt, and 2-3 Heap (Heap23).

tol

Relative tolerance below which flows towards to vertices are not considered. This will generally have no effect, but can provide speed gains when flow matrices represent spatial interaction models, in which case this parameter effectively reduces the radius from each from point over which flows are aggregated. To remove any such effect, set tol = 0.

quiet

If FALSE, display progress messages on screen.

See Also

Other distances: dodgr_distances(), dodgr_dists(), dodgr_dists_categorical(), dodgr_dists_nearest(), dodgr_flows_aggregate(), dodgr_flows_disperse(), dodgr_isochrones(), dodgr_isodists(), dodgr_isoverts(), dodgr_paths(), dodgr_times()

Examples

graph <- weight_streetnet (hampi)
from <- sample (graph$from_id, size = 10)
to <- sample (graph$to_id, size = 5)
to <- to [!to %in% from]
flows <- matrix (10 * runif (length (from) * length (to)),
    nrow = length (from)
)
graph <- dodgr_flows_aggregate (graph, from = from, to = to, flows = flows)
# graph then has an additonal 'flows' column of aggregate flows along all
# edges. These flows are directed, and can be aggregated to equivalent
# undirected flows on an equivalent undirected graph with:
graph_undir <- merge_directed_graph (graph)
# This graph will only include those edges having non-zero flows, and so:
nrow (graph)
nrow (graph_undir) # the latter is much smaller