You can use a profile to determine which edges are included in the
graph, which are accessible, etc. If for example you only handled subway
lines in the profile and disregarded all other data from OSM, you would
only be able to match things to subways.
A GPS trace from someone e.g. walking aboveground but parallel to a
subway track would also likely match to the subway rails because there
would be no more-likely candidates to match to.
Nate Wessel
Jack of all trades, Master of Geography, PhD Candidate in Urban Planning
SAUSy Lab <http://sausy.ca>, Sid Smith Hall, University of Toronto
On 04/26/2018 02:32 PM, Patrick Agin wrote:
Thanks again Nate, I will take a look for sure. But just out of
curiosity, what your ttc profile is useful for then? And how do you
(in general, big picture only) define in a profile that it's subway
only? And does it mean that when map matching against this profile,
only subway routes will be returned?
Patrick
2018-04-26 12:35 GMT-04:00 Nate Wessel <[email protected]
<mailto:[email protected]>>:
This one won't return a subway route because I haven't configured
it for that. I don't have subway trains in the dataset I'm working
with for Toronto. But it would be pretty easy to make a subway
only profile, or to add subways into this one if you want to do
all transit modes in one profile. Take a look at this page for
documentation on how profiles work:
https://github.com/Project-OSRM/osrm-backend/blob/master/docs/profiles.md
<https://github.com/Project-OSRM/osrm-backend/blob/master/docs/profiles.md>
If you want to understand how map matching in OSRM works
generally, I think this paper is a good place to start:
https://www.microsoft.com/en-us/research/wp-content/uploads/2016/12/map-matching-ACM-GIS-camera-ready.pdf
<https://www.microsoft.com/en-us/research/wp-content/uploads/2016/12/map-matching-ACM-GIS-camera-ready.pdf>
When you change the profile, you're essentially configuring the
street/rail/whatever network that your GPS trace will match
against. Montreal definitely has subways in OSM; you can see them
in the main map at openstreetmap.org <http://openstreetmap.org>.
Best,
Nate Wessel
Jack of all trades, Master of Geography, PhD Candidate in Urban
Planning
SAUSy Lab <http://sausy.ca>, Sid Smith Hall, University of Toronto
On 04/26/2018 10:52 AM, Patrick Agin wrote:
Hi Nate and thank you very much for your help. I have a very
basic question about your ttc profile (sorry if it's too silly).
When you match a GPS dataset against this profile instance, will
it return a subway route for example? If yes, why this subway
route would be declared much plausible by osrm than the street
route? Only because of the ttc profile? I realize that I don't
understand very well the involved mechanisms behind osrm and
profiles, if you can shed some light on this, I would greatly
appreciate. Another question: I suppose that the subway data has
to be included in the osm data of my city (Montreal) in order to
get subway routes from match . How can I know if it's there or
not in my osm data?
Thank you again Nate,
Patrick
2018-04-26 9:36 GMT-04:00 Nate Wessel
<[email protected] <mailto:[email protected]>>:
I've had some success with transit matching by simply
modifying the car profile to allow routing on streetcar
tracks, allowing access for buses and public service
vehicles, etc. Here's a profile I'm using for transit now:
https://github.com/SAUSy-Lab/retro-gtfs/blob/master/etc/ttc.lua#L347
<https://github.com/SAUSy-Lab/retro-gtfs/blob/master/etc/ttc.lua#L347>
I had also tried to develop a more transit specific profile
from the ground up. My thought was that known transit routes
(provided in the OSM data) would be preferred by modifying
their edge weights. This however ran into an issue with the
matching service which hasn't been resolved yet; edge weights
simply aren't used in match results.
https://github.com/Project-OSRM/osrm-backend/issues/4785
<https://github.com/Project-OSRM/osrm-backend/issues/4785>
If anyone has a suggestion for the question about multimodal
paths, I would be very keen to hear it, however I suspect
this is still an open topic of research with no definite best
practices.
Best,
Nate Wessel
Jack of all trades, Master of Geography, PhD Candidate in
Urban Planning
SAUSy Lab <http://sausy.ca>, Sid Smith Hall, University of
Toronto
On 04/26/2018 09:01 AM, Patrick Agin wrote:
Dear all,
I'm a newbie to routing engines and my first attempts are
with OSRM. Specifically I want to use the/match /service.
Questions I have is :
1) is it possible with match service to specify public
transport (e.g. subway) as the mode of transportation? I see
only profiles for car, bike and foot. If not, is there a
solution? I'm pretty sure it it possible but how? I saw in
some profiles the public_transport parameter but I don't
know how to use it.
2) is it possible for match to return a multi-modal path
given the timestamps of each coordinate? For example, return
a sub-path that is the most plausible for pedestrian (chosen
because of the low speed inferred from timestamps) followed
by another subpath that is the most plausible for car
(because of a higher speed)? Or is the only solution to
pre-process the data to infer by myself the mode of
transportation and make subsequent calls to the
corresponding profile instance?
Thanks a lot,
Patrick
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