Routes and Roads

[emantzo]

Hi, congrats on this nice work and package!
Is there a straightforward way to link the routes (produced with route()) with the actual streets (eg from osm data), to find which streets are included in each route ?
Maybe my question is naive, I am very new to this !

Thank you for your time!

[Robinlovelace]

Hi Emantzo, this is a very good question. I think the basic answer is 'yes but it could be easier'. I think the process of answering the question with reference to a reproducible example could improve the package. Do you have a reprex to illustrate how you're hoping it will work?

Basically I think a type of st_join() that only matches roads should the problem.

[mpadge]

I agree @emantzo that it is indeed a very good question, and also agree with @Robinlovelace that "it could be easier". dodgr is constructed to be able to do this, but even though doesn't do it directly. This is a proof-of-principle:

library (dodgr)
library (stplanr)
net <- readRDS ("<dodgr_streetnet>/<result>t.Rds")
xy <- sf::st_coordinates (net$geometry)
xy_i <- xy [sample (nrow (xy), size = 2), 1:2]
r <- route_dodgr (xy_i [1, ], xy_i [2, ], net = net)
head (as.matrix (r$geometry [[1]]))
#>               x        y
#> 201920 7.794609 51.92786
#> 201918 7.790919 51.92823
#> 201916 7.788843 51.92839
#> 201914 7.787338 51.92845
#> 201912 7.784688 51.92844
#> 201910 7.782649 51.92841

That matrix has row names, but they are meaningless there, because they are extracted from an sf object for which rownames play no role. dodgr internally retains rownames, and uses them to reference underlying OSM geometries, meaning that the following is possible:

net_d <- weight_streetnet (net)
p <- dodgr_paths (graph = net_d,
                  from = xy_i [1, ],
                  to = xy_i [2, ])

p <- p [[1]] [[1]] # first and only from/to pair
p_to_from <- apply (cbind (p [-length (p)], p [-1]), 1, function (i)
                    paste0 (i [1], "==", i [2]))
g_to_from <- apply (net_d [, c ("from_id", "to_id")], 1, function (i)
                    paste0 (i [1], "==", i [2]))
index <- match (p_to_from, g_to_from)
ways <- net_d$way_id [index]
head (ways)
#> [1] "146458930" "146458930" "146458930" "146458930" "146458930" "146458930"

^{Created on 2021-07-15 by the reprex package (v2.0.0.9000)}

And those are the way ID values from OSM which the route traverses. @Robinlovelace the way i see it, the only way to achieve this ability reliably is to use the dodgr approach of putting row names on sf geometries, but i strongly advise you not to do that in stplanr. I could and probably should implement this directly in dodgr, and add an option to dodgr_paths to return way IDs along with geometries which you could then directly call from route_dodgr. Either of you may feel free to open an issue in dodgr to address this if you want, and I'll gladly implement.