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Calculate isodistance contours from specified points.

Source: R/iso.R
dodgr_isodists.Rd

Calculates isodistances from input data.frame objects (graph), which must minimally contain three columns of from, to, and d or dist. If an additional column named weight or wt is present, shortest paths are calculated according to values specified in that column, while resultant isodistances are calculated from the d or dist column. That is, the paths tracing isodistances from any point will be calculated according to the minimal total sum of weight values (if present), while reported isodistances will be total sums of dist values.

Graphs derived from Open Street Map street networks, via the weight_streetnet function, have columns labelled d, d_weighted, time, and time_weighted. For these inputs, isodistances are always routed using d_weighted (or t_weighted for times), while final isodistances are sums of values of d (or t for times)- that is, of un-weighted distances or times - along those paths.

Function is fully vectorized to calculate accept vectors of central points and vectors defining multiple isodistances. Calculations use by default parallel computation with the maximal number of available cores or threads. This number can be reduced by specifying a value via RcppParallel::setThreadOptions (numThreads = <desired_number>).

Usage

dodgr_isodists(
  graph,
  from = NULL,
  dlim = NULL,
  concavity = 0,
  length_threshold = 0,
  contract = TRUE,
  heap = "BHeap"
)

Arguments

graph

data.frame or equivalent object representing the network graph. For dodgr street networks, this may be a network derived from either sf or silicate ("sc") data, generated with weight_streetnet.

from

Vector or matrix of points from which isodistances are to be calculated.

dlim

Vector of desired limits of isodistances in metres.

concavity

A value between 0 and 1, with 0 giving (generally smoother but less detailed) convex iso-contours and 1 giving highly concave (and generally more detailed) contours.

length_threshold

The minimal length of a segment of the iso-contour to be made more convex according to the 'concavity` parameter.. Low values will produce highly detailed hulls which may cause problems; if in doubt, or if odd results appear, increase this value.

contract

If TRUE, calculate isodists only to vertices in the contract graph, in other words, only to junction vertices.

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).

Value

A single data.frame of isodistances as points sorted anticlockwise around each origin (from) point, with columns denoting the from points and dlim value(s). The isodistance contours are given as id values and associated coordinates of the series of points from each from point at the specified isodistances.

See also

Other iso: dodgr_isochrones(), dodgr_isoverts()

Examples

graph <- weight_streetnet (hampi)
from <- sample (graph$from_id, size = 100)
dlim <- c (1, 2, 5, 10, 20) * 100
d <- dodgr_isodists (graph, from = from, dlim)