Franckx Laurent
2013-Jul-02 08:59 UTC
[R] passing of longitude and lattitude arguments to read URL in Google Maps and extract routes
Dear all
I try to use Google Maps to calculate travel times per transit between an origin
an destination.
The guidelines for the search can be found at:
https://developers.google.com/maps/documentation/directions/#TravelModes
When I submit the latitude and the longitude of the origin and destination as
literals, things work fine.
For instance, the following code executes correctly and we obtain the distance
and trip duration (the output of the search is in JSON format and is converted
to an R object with fromJSON)
library(rjson)
library(gooJSON)
route <-
url('http://maps.googleapis.com/maps/api/directions/json?
origin=51.13854,4.384575&destination=51.13156,4.387118®ion=be&sensor=false&mode=transit&departure_time=1372665319')
route_file <- file("route_file.json")
L <- readLines(route,-1)
writeLines(L, route_file)
close(route)
routesR_zone1_to_zone20 <- fromJSON( file = route_file )
routesR_zone1_to_zone20$routes[[1]][[3]][[1]]$distance$value/1000
routesR_zone1_to_zone20$routes[[1]][[3]][[1]]$duration$value/60
However, what I am really interested in is to repeat this operation for
thousands of origin-destination pairs. The longitude and the latitude of the
origins and destinations then become variables.
For instance:
> lat_or
[1] 51.13854
> long_or
[1] 4.384575
> lat_des
[1] 51.13156
> long_des
[1] 4.387118
> route <-
url('http://maps.googleapis.com/maps/api/directions/json?
origin=lat_or,long_or&destination=lat_des,long_des®ion=be&sensor=false&mode=transit&departure_time=1372665319')
> route_file <- file("route_file.json")
> L <- readLines(route,-1)
> writeLines(L, route_file)
> close(route)
> routesR_zone1_to_zone20 <- fromJSON( file = route_file )
> routesR_zone1_to_zone20
$routes
list()
$status
[1] "NOT_FOUND"
Thus, although the coordinates are the same as in the previous example, this
time, no route is found.
I suppose that the problem is that, when the url is accessed, lat_or etc are not
"translated" in the corresponding numeric values, and that Google
tries to calculate the route between the literals " lat_or,long_or"
and " lat_des,long_des".
Does anyone have a suggestion on how to circumvent the problem?
Laurent Franckx, PhD
VITO NV
Boeretang 200, 2400 MOL, Belgium
Tel. + 32 14 33 58 22
Skype: laurent.franckx
laurent.franckx at vito.be
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David Winsemius
2013-Jul-02 13:55 UTC
[R] passing of longitude and lattitude arguments to read URL in Google Maps and extract routes
On Jul 2, 2013, at 1:59 AM, Franckx Laurent wrote:> Dear all > > I try to use Google Maps to calculate travel times per transit between an origin an destination. > > The guidelines for the search can be found at: https://developers.google.com/maps/documentation/directions/#TravelModes > > When I submit the latitude and the longitude of the origin and destination as literals, things work fine. > > For instance, the following code executes correctly and we obtain the distance and trip duration (the output of the search is in JSON format and is converted to an R object with fromJSON) > > library(rjson) > library(gooJSON) > route <- url('http://maps.googleapis.com/maps/api/directions/json? origin=51.13854,4.384575&destination=51.13156,4.387118®ion=be&sensor=false&mode=transit&departure_time=1372665319') > route_file <- file("route_file.json") > L <- readLines(route,-1) > writeLines(L, route_file) > close(route) > routesR_zone1_to_zone20 <- fromJSON( file = route_file ) > routesR_zone1_to_zone20$routes[[1]][[3]][[1]]$distance$value/1000 > routesR_zone1_to_zone20$routes[[1]][[3]][[1]]$duration$value/60 > > > However, what I am really interested in is to repeat this operation for thousands of origin-destination pairs. The longitude and the latitude of the origins and destinations then become variables. > > For instance: > >> lat_or > [1] 51.13854 >> long_or > [1] 4.384575 >> lat_des > [1] 51.13156 >> long_des > [1] 4.387118 >> route <- url('http://maps.googleapis.com/maps/api/directions/json? origin=lat_or,long_or&destination=lat_des,long_des®ion=be&sensor=false&mode=transit&departure_time=1372665319') >> route_file <- file("route_file.json") >> L <- readLines(route,-1) >> writeLines(L, route_file) >> close(route) >> routesR_zone1_to_zone20 <- fromJSON( file = route_file ) >> routesR_zone1_to_zone20 > $routes > list() > > $status > [1] "NOT_FOUND" > > Thus, although the coordinates are the same as in the previous example, this time, no route is found. > > I suppose that the problem is that, when the url is accessed, lat_or etc are not "translated" in the corresponding numeric values, and that Google tries to calculate the route between the literals " lat_or,long_or" and " lat_des,long_des".Yes. That seems likely. R would not interpret a text literal. I don't understand why you are not using the ordinary text handling function 'paste0'. ?paste0> lat_or <- 51.13854long_or <- 4.384575 lat_des <- 51.13156 long_des <- 4.387118> paste0("origin=",lat_or,",",long_or,"&destination=",lat_des,",",long_des)[1] "origin=51.13854,4.384575&destination=51.13156,4.387118" (Also tested on Mac with R 3.0.0 RC using Google JSON Data Interpreter for R, Version: 1.0.01.) -- David.> > Does anyone have a suggestion on how to circumvent the problem? > > > > > Laurent Franckx, PhD > VITO NV > Boeretang 200, 2400 MOL, Belgium >-- David Winsemius Alameda, CA, USA