crop_gtfs: Crop a GTFS object to a spatial extent

In gtfstools: General Transit Feed Specification (GTFS) Editing and Analysing Tools

Crop a GTFS object to a spatial extent

Description

Crops a GTFS object to a spatial extent (an sf, sfc or bbox object), keeping only the stops inside it (and their parent stations) and the parts of the trips that serve them. Unlike filter_by_spatial_extent(), which keeps or drops entire trips, crop_gtfs() cuts the trips that leave the spatial extent, keeping only their stops inside it, and, by default, trims their shapes accordingly.

Usage

crop_gtfs(gtfs, geom, trim_shapes = TRUE)

Arguments

gtfs	A GTFS object, as created by read_gtfs().
geom	An sf, sfc or bbox object, in WGS 84 (EPSG 4326). Describes the spatial extent used to crop the data. Stops on its boundary are considered inside it. A bbox is compared directly with the stops' coordinates, while sf and sfc objects are tested with sf::st_intersects(), whose edges are geodesics when spherical geometry is used (the default in {sf}), so stops very close to their edges may be considered outside. Bounding boxes crossing the antimeridian are not supported.
trim_shapes	A logical. Whether the shapes of the trips that leave the spatial extent should be trimmed to the part between their first and last stops inside it (defaults to TRUE). If FALSE, these trips keep their entire shapes.

Value

The GTFS object passed to the gtfs parameter, after the cropping process.

Details

The stop_times entries at stops outside the spatial extent are dropped. Trips left with fewer than two stop_times entries are dropped, as are the entries related to them in other tables, as in filter_by_trip_id(). A trip that leaves the spatial extent and enters it again keeps the stops inside it, with gaps in their stop_sequence. The resulting stops table includes the stops inside the spatial extent served by the remaining trips, the entrances, generic nodes and boarding areas inside it related to these stops, and their parent stations, even if these lie outside the spatial extent. Stops without coordinates are considered outside of it, so generic nodes and boarding areas without coordinates, and the pathways that link to them, are dropped.

GTFS requires times at the first and last stops of each trip. If the new first or last stop of a cropped trip has blank times, the blank times of the trip are interpolated with interpolate_stop_times() (along its shape, or along straight lines between stops if the trip is not linked to a shape), before the trip is cropped. Intermediate blank times of these trips are thus filled too. Times that can't be interpolated (see interpolate_stop_times()) are left blank, with a warning. If a cropped trip is listed in frequencies, the start_time and end_time of its entries are shifted by the time between the departure (or the arrival, if the departure is blank) at its original first stop and at its new one, since they refer to the first stop of the trip. Entries whose shift can't be calculated (e.g. because of blank times) or is negative are kept unchanged.

With trim_shapes = TRUE, the stops of each cropped trip are located along its shape, as in get_trip_length(), and its shape is cut from its first to its last remaining stop, keeping the parts of the shape outside the spatial extent between them. A shape cut in only one way keeps its shape_id. If a shape is cut in different ways, or is also used by trips that are not cut, each cut gets a new shape_id ("<shape_id>_1", "<shape_id>_2", etc., different from any shape_id already in use). The shape_dist_traveled of the new shape points and of the stop_times entries of the trips linked to them is set to NA, because the distance unit used by the feed is unknown. Trips not linked to a usable shape keep their shape unchanged.

See Also

filter_by_spatial_extent(), interpolate_stop_times()

Examples

data_path <- system.file("extdata/spo_gtfs.zip", package = "gtfstools")
gtfs <- read_gtfs(data_path)

bbox <- sf::st_bbox(
  c(xmin = -46.66, ymin = -23.57, xmax = -46.62, ymax = -23.53),
  crs = 4326
)
object.size(gtfs)

# keeps only the stops inside the bounding box and trims the shapes
cropped_gtfs <- crop_gtfs(gtfs, bbox)
object.size(cropped_gtfs)

# keeps the entire shapes of the cropped trips
cropped_gtfs <- crop_gtfs(gtfs, bbox, trim_shapes = FALSE)
object.size(cropped_gtfs)

gtfstools documentation built on Oct. 28, 2026, 5:13 p.m.