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Calculate isodistance or isochrone vertices from specified points.

Source: R/iso.R
dodgr_isoverts.Rd

Returns lists of all network vertices contained within isodistance or isochrone contours. Input objects must be 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, iso contours are evaluate via shortest paths calculated according to values specified in that column, while resultant values of iso contours are calculated from the d or dist column. That is, the paths tracing iso contours from any point will be calculated according to the minimal total sum of weight values (if present), while reported iso contours 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, iso contours are always routed using d_weighted (or t_weighted for times), while final iso contours reflect 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 accept vectors of central points and vectors defining multiple isochrone or isodistance thresholds. Provide one or more dlim values for isodistances, or one or more tlim values for 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_isoverts(graph, from = NULL, dlim = NULL, tlim = NULL, 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 isodistances or isochrones are to be calculated.

dlim

Vector of desired limits of isodistances in metres.

tlim

Vector of desired limits of isochrones in seconds

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 vertex IDs, 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.

Isoverts 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_isochrones(), dodgr_isodists()

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_isoverts (graph, from = from, tlim)
} # }