Re: [OSRM-talk] Map-matching transit vehicles: giving preference to known routes?

[Daniel Hofmann]

Actually we base map matching on the distance of _the fastest path_ here:

https://github.com/Project-OSRM/osrm-backend/blob/a63b43c259d49fc4915810eb4bfdd86bc78bce93/src/engine/routing_algorithms/map_matching.cpp#L220-L226

I got confused a bit this morning because `getNetworkDistance` does this
two levels of indirection approach.

So if you set edge weights in the profiles accordingly (based on if a way
is a transit-relevant way or not) orsm will find the fastest route and then
does map matching on it based on its distance.

Hope that helps

On Mon, May 22, 2017 at 10:38 AM, Daniel Hofmann  wrote:

> Did you see the profile docs here? Granted they could be more detailed but
> should get you started. If you have anything to add we're always happy for
> pull requests :)
>
> https://github.com/Project-OSRM/osrm-backend/blob/master/docs/profiles.md
>
> What I can suggest is to
> - always provide timestamps otherwise defaults will be used internally
> - investigate the map matching's tidy option for blob removal (think:
> waiting at a traffic signal)
>
> Unfortunately map matching is distance based so modifying edge weights or
> speeds in the profiles won't help.
> And completely discarding ways won't help you either since you
> specifically want to capture detours.
>
> Maybe have a look at Figure 7 in the map matching paper "Hidden Markov Map
> Matching Through Noise and Sparseness. And then just give it a try with
> your data and see how it goes.
>
> There are probably other ways to do your analysis, e.g. map match your
> traces on a regular profile and then compare the results against a osrm
> route query on a transit-ish profile.
> For this transit-ish profile you could set low weights (note: modify
> weights, keep speeds for correct ETAs) except for actual transit routes. I
> don't know if the transit data is good enough for this, though.
>
> Interested in what you find out.
>
> On Mon, May 22, 2017 at 2:02 AM, Nate Wessel  > wrote:
>
>> Hi all,
>>
>> I have recently been using OSRM to do map-matching for transit vehicles,
>> with locations from historical GPS data. The documentation on creating
>> profiles is pretty minimal from what I can tell, so I've just been able to
>> make a few modifications to the car.lua profile to allow vehicles to go on
>> streetcar tracks, agency service roads, etc.
>>
>> The data I've been playing with so far has a ~20second sampling
>> frequency, which has worked well, but I'm about to start working with data
>> that has a lower sampling rate (30-60secs) and I'm worried that I'll get a
>> lot of spurious matches. I was wondering if it is possible to modify the
>> profile such that a strong preference is given to known transit routes
>> (which are tagged with route relations in OSM). Transit almost always
>> follows a known route, but sometimes it detours, and it's important to my
>> research to be able to capture that in matched GPS data.
>>
>> What might be a good way to add this to a routing profile? Does
>> everything in the profile come down to speed, access, and node-related
>> penalties? Would I want to artificially inflate the "speed" of
>> transit-served streets? Is there more thorough documentation on profiles
>> somewhere than what is provided here
>> ?
>>
>> The profile I've been using is:
>> https://github.com/SAUSy-Lab/retro-gtfs/blob/master/etc/ttc.lua
>>
>> Any help would be greatly appreciated!
>> --
>> Nate Wessel
>> Jack of all trades, Master of Geography
>> SAUSy Lab , Sid Smith Hall
>>
>> ___
>> OSRM-talk mailing list
>> OSRM-talk@openstreetmap.org
>> https://lists.openstreetmap.org/listinfo/osrm-talk
>>
>>
>
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Re: [OSRM-talk] Map-matching transit vehicles: giving preference to known routes?

[Daniel Hofmann]

Did you see the profile docs here? Granted they could be more detailed but
should get you started. If you have anything to add we're always happy for
pull requests :)

https://github.com/Project-OSRM/osrm-backend/blob/master/docs/profiles.md

What I can suggest is to
- always provide timestamps otherwise defaults will be used internally
- investigate the map matching's tidy option for blob removal (think:
waiting at a traffic signal)

Unfortunately map matching is distance based so modifying edge weights or
speeds in the profiles won't help.
And completely discarding ways won't help you either since you specifically
want to capture detours.

Maybe have a look at Figure 7 in the map matching paper "Hidden Markov Map
Matching Through Noise and Sparseness. And then just give it a try with
your data and see how it goes.

There are probably other ways to do your analysis, e.g. map match your
traces on a regular profile and then compare the results against a osrm
route query on a transit-ish profile.
For this transit-ish profile you could set low weights (note: modify
weights, keep speeds for correct ETAs) except for actual transit routes. I
don't know if the transit data is good enough for this, though.

Interested in what you find out.

On Mon, May 22, 2017 at 2:02 AM, Nate Wessel 
wrote:

> Hi all,
>
> I have recently been using OSRM to do map-matching for transit vehicles,
> with locations from historical GPS data. The documentation on creating
> profiles is pretty minimal from what I can tell, so I've just been able to
> make a few modifications to the car.lua profile to allow vehicles to go on
> streetcar tracks, agency service roads, etc.
>
> The data I've been playing with so far has a ~20second sampling frequency,
> which has worked well, but I'm about to start working with data that has a
> lower sampling rate (30-60secs) and I'm worried that I'll get a lot of
> spurious matches. I was wondering if it is possible to modify the profile
> such that a strong preference is given to known transit routes (which are
> tagged with route relations in OSM). Transit almost always follows a known
> route, but sometimes it detours, and it's important to my research to be
> able to capture that in matched GPS data.
>
> What might be a good way to add this to a routing profile? Does everything
> in the profile come down to speed, access, and node-related penalties?
> Would I want to artificially inflate the "speed" of transit-served streets?
> Is there more thorough documentation on profiles somewhere than what is
> provided here 
> ?
>
> The profile I've been using is:
> https://github.com/SAUSy-Lab/retro-gtfs/blob/master/etc/ttc.lua
>
> Any help would be greatly appreciated!
> --
> Nate Wessel
> Jack of all trades, Master of Geography
> SAUSy Lab , Sid Smith Hall
>
> ___
> OSRM-talk mailing list
> OSRM-talk@openstreetmap.org
> https://lists.openstreetmap.org/listinfo/osrm-talk
>
>
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