# osrmr

#### 2021-05-31

‘osrmr’ is a little R package designed to easily access and use the OSRM (open source routing machine - http://project-osrm.org/) directly from R.

Many problems with geocoding tasks can be solved in R. Yet, there is no direct routing engine implemented. For such tasks, OSRM is a widely used tool to access geospacial data and solve routing problems. The ‘osrmr’ package gives the possibility to access a basic functionality of OSRM.

### server

You can access the OSRM-routing-engine with the onlinehost of OSRM (API 5) or by running a localhost of OSRM (API 4 or 5) on your device. As far as I know, there is no simple way to access the onlinehost of the OSRM API 4.

In order to use the localhost you need a local build of the OSRM-routing-engine (https://github.com/Project-OSRM/osrm-backend/wiki/Building-OSRM). Keep the local build in a directory of your choice. This directory should contain a map of the area you want to work with (i.e. "switzerland-latest.osrm", "germany-latest.osrm", "great-britain.osrm", …) and other data and scripts.

• Start your localhost by calling run_server()
• run_server() returns the error_code of the starting-attempt (0 means the start was successful)
• You’re now set up to use the functionalities of the ‘osrmr’ package
• After finishing all calculations you can stop your localhost with the function by calling quit_server()
• It’s recommended to use an Environment Variable for the path of your local build (see examples).
library(osrmr)

# Set the path of your localhost as environment variable
Sys.setenv("OSRM_PATH"="C:/OSRM_API5")

# start localhost of OSRM
run_server("switzerland-latest.osrm")
quit_server() # quit the running server

## use OSRM in R

With the ‘osrmr’ package you can use the following basic functionalities of OSRM:

The coordinate-standard for all functionalities of ‘osrmr’ is WGS84.

Keep in mind that different API’s and localhost/onlinehost may return different results. There are pro’s and con’s for using one specific configuration. When choosing your configuration keep the following points in mind:

• The onlinehost is always most up-to-date. You can be sure to make calculations with very up-to-date maps and routing-engines.
• The onlinehost might sometimes not be available due to maintenance or connection problems.
• The onlinehost is slower than the localhost since every calculation represents an individual request to the OSRM server.
• The localhost is a fixed build which stays the same - so be cautious not to get out of date…
• The localhost is always available.

### nearest

For given coordinates, you can calculate the nearest position which can be accessed by car by using the function nearest(). You can specify the coordinates, the API version and whether to use the localhost or not.

library(osrmr)
nearest(lat = 47, lng = 8, api_version = 5, localhost = FALSE)
run_server("switzerland-latest.osrm")
nearest(lat = 47, lng = 8, api_version = 5, localhost = TRUE)
quit_server()
#        lat      lng
# 1 47.00008 8.003016

Results may differ depending on the api version and the build of the localhost (or onlinehost).

### viaroute

For a given start- and end-destination, you can access route informations using viaroute(). OSRM chooses the nearest point which can be accessed by car for the start- and end-destination. You can choose whether to return only the traveltime (in seconds, as numeric) or more details of the route (as list), by setting the parameter instructions.

viaroute(lat1 = 47.1, lng1 = 8.1, lat2 = 46.9, lng2 = 8.3, instructions = FALSE,
api_version = 5, localhost = FALSE)

viaroute(lat1 = 47.1, lng1 = 8.1, lat2 = 46.9, lng2 = 8.3, instructions = TRUE,
api_version = 5, localhost = FALSE)

### decoder

Use decode_geom() to decode polylines. Polylines can be generated with OSRM (see example below). Depending on the OSRM API version, the precision for [lat, lng] encoding is different.

• API 4 used “polyline” with precision 5 (1e-5)
• API 5 uses “polyline6” with precision 6 (1e-6)

To decode a polyline the right way you need to know the precision of the polyline. The parameter precision of decode_geom() accepts the values 5 (1e-5) or 6 (1e-6) to decode a polyline.

polyline_5 <- rjson::fromJSON(file = "http://router.project-osrm.org/route/v1/driving/8.1,47.1;8.3,46.9?steps=false&geometries=polyline")$routes[[1]]$geometry
polyline_6 <- rjson::fromJSON(file = "http://router.project-osrm.org/route/v1/driving/8.1,47.1;8.3,46.9?steps=false&geometries=polyline6")$routes[[1]]$geometry

decoded_5 <- decode_geom(polyline_5, precision = 5)
decoded_6 <- decode_geom(polyline_6, precision = 6)

options(digits = 10)
decoded_5[1:5,]
decoded_6[1:5,]

nrow(decoded_5)
nrow(decoded_6)

The differences of precisions 5 and 6 are smaller than a tolerance of 1e-6.

assertthat::assert_that(all.equal(decoded_5, decoded_6, tolerance = 1e-6))
Sys.unsetenv("OSRM_PATH")