knitr::opts_chunk$set( collapse = TRUE, comment = "#>" )
Package gtfs2gps
allows users to convert public transport GTFS data into a single data.table
format with GPS-like records, which can then be used in various applications such as running transport simulations or scenario analyses. Before using the package, just install it from GitHub.
install.packages("gtfs2gps")
After loading the package, GTFS data can be read into R by using read_gtfs()
.
This function gets a zipped GTFS file and returns a list of data.table
objects. The returning list contains the data of each GTFS file indexed according to their file names without extension.
library("gtfs2gps") poa <- read_gtfs(system.file("extdata/poa.zip", package ="gtfs2gps")) names(poa) head(poa$trips)
Note that not all GTFS files are loaded into R. This function only loads the necessary data to spatially and temporally handle trips and stops, which are:
"shapes.txt", "stop_times.txt", "stops.txt", "trips.txt",
"agency.txt", "calendar.txt", "routes.txt", and "frequencies.txt", with
this last four being optional.
If a given GTFS zipped file does not contain all of these required files then read_gtfs()
will stop with an error.
In the code below we filter only the shape ids `c("T2-1", "A141-1") to allow faster execution the next scripts.
object.size(poa) |> format(units = "Kb") poa_small <- gtfstools::filter_by_shape_id(poa, c("T2-1", "A141-1")) object.size(poa_small) |> format(units = "Kb")
We can then easily convert the data to simple feature format and plot them.
poa_small_shapes_sf <- gtfs2gps::gtfs_shapes_as_sf(poa_small) poa_small_stops_sf <- gtfs2gps::gtfs_stops_as_sf(poa_small) plot(sf::st_geometry(poa_small_shapes_sf)) plot(sf::st_geometry(poa_small_stops_sf), pch = 20, col = "red", add = TRUE) box()
After subsetting the data, it is also possible to save it as a new GTFS file using write_gtfs()
, as shown below.
temp_gtfs <- tempfile(pattern = 'poa_small', fileext = '.zip') gtfs2gps::write_gtfs(poa_small, temp_gtfs)
To convert GTFS to GPS-like format, use gtfs2gps()
. This is the core function of the package. It takes a GTFS zipped file as an input and returns a data.table
where each row represents a 'GPS-like' data point for every trip in the GTFS file. In summary, this function interpolates the space-time position of each vehicle in each trip considering the network distance and average speed between stops. The function samples the timestamp of each vehicle every $15m$ by default, but the user can set a different value in the spatial_resolution
argument. See the example below.
poa_gps <- gtfs2gps(temp_gtfs, spatial_resolution = 100) head(poa_gps)
The following figure maps the first 100 data points of the sample data we processed. They can be converted to simple feature
points or linestring.
poa_gps60 <- poa_gps[1:100, ] # points poa_gps60_sfpoints <- gps_as_sfpoints(poa_gps60) # linestring poa_gps60_sflinestring <- gps_as_sflinestring(poa_gps60) # plot plot(sf::st_geometry(poa_gps60_sfpoints), pch = 20) plot(sf::st_geometry(poa_gps60_sflinestring), col = "blue", add = TRUE) box()
The function gtfs2gps()
automatically recognizes whether the GTFS data brings detailed stop_times.txt
information or whether it is a frequency.txt
GTFS file. A sample data of a GTFS with detailed stop_times.txt
cab be found below:
poa <- system.file("extdata/poa.zip", package ="gtfs2gps") poa_gps <- gtfs2gps(poa, spatial_resolution = 50) poa_gps_sflinestrig <- gps_as_sfpoints(poa_gps) plot(sf::st_geometry(poa_gps_sflinestrig[1:200,])) box()
For a given trip, the function gtfs2gps
calculates the average speed between each pair of consecutive stops given by the ratio between cumulative network distance S
and departure time t
for a consecutive pair of valid stop_ids (i
),
knitr::include_graphics("https://github.com/ipeaGIT/gtfs2gps/blob/master/man/figures/equation1.png?raw=true")
Since the beginning of each trip usually starts before the first stop_id, the mean speed cannot be calculated as shown in the previous equation because information on i
period does not exist. In this case, the function consider the mean speed for the whole trip. It also happens after the last valid stop_id (N
) of the trips, where info on i + 1
also does not exist.
knitr::include_graphics("https://github.com/ipeaGIT/gtfs2gps/blob/master/man/figures/speed.PNG?raw=true")
If you have any suggestions or want to report an error, please visit the GitHub page of the package here.
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