/journeys: How do I get the total distance of a journey?

[JennsiS]

Hello! i couldn't find on the documentation more info about the body response for /journeys endpoint. I want to know if i can get the total distance of a journey? and in which measure unit?

[derhuerst]

Hello! 👋

As db-rest is just a thin wrapper around hafas-rest-api@5, which uses hafas-client@6 do fetch the data, the /journeys endpoint's response is determined by hafas-client@6.

If you pass ?polylines=true, you will get journeys with a polyline on each leg. The docs on this are quite sparse and hidden:

From hafas-client's journeys() docs:

If you pass polylines: true, each journey leg will have a polyline field. Refer to the section in the trip() docs for details.

From hafas-client's trip() docs:

If you pass polyline: true, the trip will have a polyline field, containing a GeoJSON FeatureCollection of Points. Every Point next to a station will have properties containing the station's metadata.

We'll look at an example for U6 from Alt-Mariendorf to Alt-Tegel, taken from the VBB profile:

{
	type: 'FeatureCollection',
	features: [
		{
			type: 'Feature',
			properties: {
				type: 'station',
				id: '900000070301',
				name: 'U Alt-Mariendorf',
				/* … */
			},
			geometry: {
				type: 'Point',
				coordinates: [13.3875, 52.43993] // longitude, latitude
			}
		},
		/* … */
		{
			type: 'Feature',
			properties: {
				type: 'station',
				id: '900000017101',
				name: 'U Mehringdamm',
				/* … */
			},
			geometry: {
				type: 'Point',
				coordinates: [13.38892, 52.49448] // longitude, latitude
			}
		},
		/* … */
		{
			// intermediate point, without associated station
			type: 'Feature',
			properties: {},
			geometry: {
				type: 'Point',
				coordinates: [13.28599, 52.58742] // longitude, latitude
			}
		},
		{
			type: 'Feature',
			properties: {
				type: 'station',
				id: '900000089301',
				name: 'U Alt-Tegel',
				/* … */
			},
			geometry: {
				type: 'Point',
				coordinates: [13.28406, 52.58915] // longitude, latitude
			}
		}
	]
}

You can determine each leg's distance by, for each of the journey's legs,
a. transforming the GeoJSON FeatureCollection into a GeoJSON LineString,
b. using either Turf's distance() (to get the "crow-flight distance") or Turf's length() (to get the travelled distance),
c. summing these distances up to get the journey's total distance.

Does that answer your question?

[derhuerst]

I'll close this issue. Please re-open if you question is not answered.

[JennsiS]

Hello @derhuerst, sorry for the delay. Thank you for your response it was very helpful and clear.