dodgr_distances: Calculate matrix of pair-wise distances between points.

Description

Alias for dodgr_dists

Usage

dodgr_distances(
  graph,
  from = NULL,
  to = NULL,
  shortest = TRUE,
  pairwise = FALSE,
  heap = "BHeap",
  parallel = TRUE,
  quiet = TRUE
)

Value

square matrix of distances between nodes

Arguments

graph

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

The from and to columns of graph may be either single columns of numeric or character values specifying the numbers or names of graph vertices, or combinations to two columns specifying geographical (longitude and latitude,) coordinates. In the latter case, almost any sensible combination of names will be accepted (for example, fromx, fromy, from_x, from_y, or fr_lat, fr_lon.)

Note that longitude and latitude values are always interpreted in 'dodgr' to be in EPSG:4326 / WSG84 coordinates. Any other kinds of coordinates should first be reprojected to EPSG:4326 before submitting to any 'dodgr' routines.

See further information in Details.

from

Vector or matrix of points from which route distances are to be calculated, specified as one of the following:

Single character vector precisely matching node numbers or names given in graph$from or graph$to.
Single vector of integer-ish values, in which case these will be presumed to specify indices into dodgr_vertices, and NOT to correspond to values in the 'from' or 'to' columns of the graph. See the example below for a demonstration.
Matrix or equivalent of longitude and latitude coordinates, in which case these will be matched on to the nearest coordinates of 'from' and 'to' points in the graph.

to

Vector or matrix of points to which route distances are to be calculated. If to is NULL, pairwise distances will be calculated from all from points to all other nodes in graph. If both from and to are NULL, pairwise distances are calculated between all nodes in graph.

shortest

If FALSE, calculate distances along the fastest rather than shortest routes. For street networks produced with weight_streetnet, distances may also be calculated along the fastest routes with the shortest = FALSE option. Graphs must in this case have columns of time and time_weighted. Note that the fastest routes will only be approximate when derived from sf-format data generated with the osmdata function osmdata_sf(), and will be much more accurate when derived from sc-format data generated with osmdata_sc(). See weight_streetnet for details.

pairwise

If TRUE, calculate distances only between the ordered pairs of from and to.

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`).

parallel

If TRUE, perform routing calculation in parallel. Calculations in parallel ought very generally be advantageous. For small graphs, calculating distances in parallel is likely to offer relatively little gain in speed, but increases from parallel computation will generally markedly increase with increasing graph sizes. By default, parallel computation uses the maximal number of available cores or threads. This number can be reduced by specifying a value via RcppParallel::setThreadOptions (numThreads = <desired_number>). Parallel calculations are, however, not able to be interrupted (for example, by Ctrl-C), and can only be stopped by killing the R process.

quiet

If FALSE, display progress messages on screen.

Details

graph must minimally contain three columns of from, to, dist. If an additional column named weight or wt is present, shortest paths are calculated according to values specified in that column; otherwise according to dist values. Either way, final distances between from and to points are calculated by default according to values of dist. That is, paths between any pair of points will be calculated according to the minimal total sum of weight values (if present), while reported distances will be total sums of dist values.

Examples

Run this code

# A simple graph
graph <- data.frame (
    from = c ("A", "B", "B", "B", "C", "C", "D", "D"),
    to = c ("B", "A", "C", "D", "B", "D", "C", "A"),
    d = c (1, 2, 1, 3, 2, 1, 2, 1)
)
dodgr_dists (graph)

# Example of "from" and "to" as integer-ish values, in which case they are
# interpreted to index into "dodgr_vertices()":
graph <- data.frame (
    from = c (1, 3, 2, 2, 3, 3, 4, 4),
    to = c (2, 1, 3, 4, 2, 4, 3, 1),
    d = c (1, 2, 1, 3, 2, 1, 2, 1)
)
dodgr_dists (graph, from = 1, to = 2)
# That then gives distance from "1" to "3" because the vertices are built
# sequentially along "graph$from":
dodgr_vertices (graph)
# And vertex$id [2] is "3"

# A larger example from the included [hampi()] data.
graph <- weight_streetnet (hampi)
from <- sample (graph$from_id, size = 100)
to <- sample (graph$to_id, size = 50)
d <- dodgr_dists (graph, from = from, to = to)
# d is a 100-by-50 matrix of distances between `from` and `to`

if (FALSE) {
# a more complex street network example, thanks to @chrijo; see
# https://github.com/UrbanAnalyst/dodgr/issues/47

xy <- rbind (
    c (7.005994, 51.45774), # limbeckerplatz 1 essen germany
    c (7.012874, 51.45041)
) # hauptbahnhof essen germany
xy <- data.frame (lon = xy [, 1], lat = xy [, 2])
essen <- dodgr_streetnet (pts = xy, expand = 0.2, quiet = FALSE)
graph <- weight_streetnet (essen, wt_profile = "foot")
d <- dodgr_dists (graph, from = xy, to = xy)
# First reason why this does not work is because the graph has multiple,
# disconnected components.
table (graph$component)
# reduce to largest connected component, which is always number 1
graph <- graph [which (graph$component == 1), ]
d <- dodgr_dists (graph, from = xy, to = xy)
# should work, but even then note that
table (essen$level)
# There are parts of the network on different building levels (because of
# shopping malls and the like). These may or may not be connected, so it may
# be necessary to filter out particular levels
index <- which (!(essen$level == "-1" | essen$level == "1")) # for example
library (sf) # needed for following sub-select operation
essen <- essen [index, ]
graph <- weight_streetnet (essen, wt_profile = "foot")
graph <- graph [which (graph$component == 1), ]
d <- dodgr_dists (graph, from = xy, to = xy)
}