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Calculate isochrone contours from specified points.

Source: R/iso.R
dodgr_isochrones.Rd

Calculates isochrones from input data.frame objects (graph), which must minimally contain three columns of from, to, and t or time. If an additional column named t_weight or t_wt is present, fastest paths are calculated according to values specified in that column, while resultant isochrones are calculated from the t or time column. That is, the paths tracing isochrones from any point will be calculated according to the minimal total sum of t_weight values (if present), while reported isochrones will be total sums of time 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, isochrones are always routed using t_weighted, while final isochrones are sums of values of t - 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 isochrones. 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_isochrones(
  graph,
  from = NULL,
  tlim = NULL,
  concavity = 0,
  length_threshold = 0,
  heap = "BHeap"
)

Arguments

graph

data.frame or equivalent object representing the network graph. For dodgr street networks, this must be a network derived from silicate ("sc") data, generated with weight_streetnet. This function does not work with networks derived from sf data.

from

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

tlim

Vector of desired limits of isochrones in seconds

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.

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 isochrones as points sorted anticlockwise around each origin (from) point, with columns denoting the from points and tlim value(s). The isochrones are given as id values and associated coordinates of the series of points from each from point at the specified isochrone times.

Isochrones are calculated by default using 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>).

See also

Other iso: dodgr_isodists(), dodgr_isoverts()

Examples

if (FALSE) { # \dontrun{
# Use osmdata package to extract 'SC'-format data:
library (osmdata)
dat <- opq ("hampi india") %>%
    add_osm_feature (key = "highway") %>%
    osmdata_sc ()
graph <- weight_streetnet (dat)
from <- sample (graph$.vx0, size = 100)
tlim <- c (5, 10, 20, 30, 60) * 60 # times in seconds
x <- dodgr_isochrones (graph, from = from, tlim)
} # }