OSRM wrong waypoint index? - osrm

Question

I'm trying to use OSRM to get a list of locations ordered by the distance between them. For that I'm using the Trip service (https://github.com/Project-OSRM/osrm-backend/blob/master/docs/http.md#trip-service).
Given the encoded polyline:
omq~Fji_vOg#sHQcnAjCtrAkCs|AvHpcBwCeeB
I receive the following:
"waypoints": [
{
"waypoint_index": 0,
"trips_index": 0,
"hint": "RzfEg1U3xIPaAAAAJgAAAAAAAAAAAAAANgAAAAoAAAAAAAAAAAAAAHM6AACFecb6__B-AoR5xvoQ8X4CAACPBd_PZ4A=",
"name": "",
"location": [
-87.656059,
41.873663
]
},
{
"waypoint_index": 2,
"trips_index": 0,
"hint": "OTfEg5M4xINDAwAAnwEAAAAAAAAAAAAA0AAAAGgAAAAAAAAAAAAAAHM6AACJf8b6xvF-Aoh_xvrY8X4CAADPEN_PZ4A=",
"name": "",
"location": [
-87.654519,
41.873862
]
},
{
"waypoint_index": 5,
"trips_index": 0,
"hint": "WuVchFzlXIQ6AwAAbwUAAAAAAAAAAAAAzgAAAFwBAAAAAAAAAAAAAHM6AAD3sMb6EPN-Avywxvoy8n4CAACfBd_PZ4A=",
"name": "",
"location": [
-87.641865,
41.874192
]
},
{
"waypoint_index": 1,
"trips_index": 0,
"hint": "PDfEg343xIOuAQAAggQAAAAAAAAAAAAAawAAACEBAAAAAAAAAAAAAHM6AACsfMb6su9-Aq58xvp2734CAADPEN_PZ4A=",
"name": "",
"location": [
-87.655252,
41.87333
]
},
{
"waypoint_index": 3,
"trips_index": 0,
"hint": "VuVchFjlXITqAQAA0QEAAAAAAAC1BAAAegAAAHUAAAAAAAAALQEAAHM6AACYtsb6L_J-AjK3xvoy8n4CAABvFt_PZ4A=",
"name": "",
"location": [
-87.640424,
41.873967
]
},
{
"waypoint_index": 6,
"trips_index": 0,
"hint": "6WJUhBgEhoTTBAAAdgQAAAAAAAAAAAAANAEAAB4BAAAAAAAAAAAAAHM6AAAJesb6H-x-Alh4xvoa7H4CAAB_Ft_PZ4A=",
"name": "",
"location": [
-87.655927,
41.872415
]
},
{
"waypoint_index": 4,
"trips_index": 0,
"hint": "TOVchFDlXIRTAgAAhQEAACoAAADuAAAAlAAAAGIAAAAKAAAAPAAAAHM6AAAtuMb6FvB-Aja4xvoS734CAQCPBd_PZ4A=",
"name": "",
"location": [
-87.640019,
41.87343
]
}
]
URL for testing: http://router.project-osrm.org/trip/v1/driving/polyline(omq~Fji_vOg#sHQcnAjCtrAkCs|AvHpcBwCeeB)?overview=false
This is how they were plotted (for better understanding):
If I understood the docs correctly, waypoint_index was supposed to provide the order of the locations by distance. If so, it doesn't seem to be working given the result. Check it here:
Wanted
Group 1
lat: 41.87368, lon: -87.65606
lat: 41.87388, lon: -87.65452
lat: 41.87327, lon: -87.65525
lat: 41.87241, lon: -87.65636
Group 2
lat: 41.87317, lon: -87.64001
lat: 41.87397, lon: -87.64186
lat: 41.87397, lon: -87.64027
Actual
Group 1
lat: 41.873663, lon: -87.656059
lat: 41.87333, lon: -87.655252
lat: 41.873862, lon: -87.654519
Group 2
lat: 41.873967, lon: -87.640424
lat: 41.87343, lon: -87.640019
lat: 41.874192, lon: -87.641865
Group 1
lat: 41.872415, lon: -87.655927
As you can see the order provided by waypoint_index under Actual does exclude the last item from its supposed group (1). I think this might be related to the roundtrip option, is this the case? If so, is there an option I can set on the trip service that will provide me with the result I need?
Or, is there another service that will receive a list of locations and return them ordered by the distance between them? Given that I can't provide the start/end.
I'd like to just send a list of locations and receive them ordered by proximity, not using roundtrip (if that's what's breaking the previous request).
Thanks!

Answer 1

ordered by the distance between them
What the trip service does is order them in a way that minimizes the total drive-time if you need to visit all waypoints, not cluster them by straight-line distance.
If you look at the route that was actually generated, the order makes sense: It is a circular trip that includes all provides locations (and at least looks optimal)