[pgrouting-dev] Support for Time Constraints
Stephen Woodbridge
woodbri at swoodbridge.com
Thu Jun 2 22:47:15 EDT 2011
On 6/2/2011 10:35 PM, Jay Mahadeokar wrote:
> Hi Daniel,
>
> On Fri, Jun 3, 2011 at 7:45 AM, Daniel Kastl <daniel at georepublic.de
> <mailto:daniel at georepublic.de>> wrote:
>
> Hi Jay,
>
> Maybe I'm wrong, but I'm not sure it's really necessary to have
> "live" traffic feeds available to make use of TDSP.
> It will be hard to get such data for free and it's difficult to
> guess how such data might be organized.
>
> But for my understanding "time-dependent" doesn't need to go that
> far to support such kind of feeds.
> Time constraints can be simple access restrictions to parts of your
> network at certain times for example.
>
> Test data can be very simple at the beginning and self made in my
> opinion. If at a later time it appears that there is functionality
> missing to support traffic feeds, then this can be added at a later
> time.
>
> So for some sample data these cases come to my mind:
>
> * highways in urban areas have a speed limit during night times
> to reduce the noise
> * some roads in city centers are closed for cars during business
> hours
> * roads may have different cost in each direction in the
> morning, when people drive to work, and in the evening when
> the drive back home.
>
> In Germany these three examples are common and will also
> be available in OSM someday, I guess.
>
> What do you think?
>
>
> I agree. I have the same application in mind when it comes to
> time-dependent shortest paths. But again, its difficult to obtain this
> data. One work-around is that I can use the pgRouting-workshop "ways"
> table, and generate an additional time-dependent-cost table with random
> travel times for every edge_id, say for 24 - hour time cycles, intervals
> of 1 hour each. This can serve as good enough test data I think. We can
> also add some more logic to randomness and say tune the travel_times
> according to rush hours etc, (but that wont affect the algorithm, just
> the output! )
>
> I was more interested in real-world actual data, than randomly generated
> data because that would also be useful in my college thesis work in
> future. But from GSoc point of view, such data would be a luxury!
Hi Jay,
I think that instead of just random times, I would take a different
approach to generate this data. If we think about "rush hour" around a
major city, the highways (based on road class) flowing into the city in
the morning would get reduced average speeds you could apply curve like
average speed*percent based on 6am (90%), 7am(75%), 8am(45%), 9am(50%),
10am(85%) and do something similar in the evening rush. It might be too
hard to figure on direction of flow in/out bound so apply the curve to
all traffic. The assumption is that the highways are congested which
will force traffic onto side streets. You might want to also reduce the
lower class speeds by say a constant 80% during rush hour.
If we can get OSM data then it should be easy to populate the table with
that data.
-Steve
> Daniel
>
> 2011/5/27 Jay Mahadeokar <jai.mahadeokar at gmail.com
> <mailto:jai.mahadeokar at gmail.com>>
>
> Hi,
>
> We had discussed some possible ways of getting the test
> time-dependent data, but reached no particular solution.
>
> I found this link: http://bhelp.traffic.com/
>
> It a Navteq service and provides live traffic information. You
> need to login, and then you can browse live traffic.
> You can select each road and get following info:
>
> - Jam factor
> - Drive time now
> - delay
> - speed limit
> - average speed
>
> I guess, this is exactly what we need. Even if we can record the
> drive-time now, for each road at intervals of 1 hour each for a
> particular city, we will have significant time dependent data.
>
> I browsed the website but did not find any link where this data
> is made available. Is there any way to record this data? Any
> starting points?
>
> On Thu, Apr 7, 2011 at 10:05 PM, Jay Mahadeokar
> <jai.mahadeokar at gmail.com <mailto:jai.mahadeokar at gmail.com>> wrote:
>
> Hello all,
>
> Just an update - as Daniel suggested I posted a query about
> time-Dependent data in OSM routing list. It seems they dont
> have such data, but people have posted some things that
> might be useful for us in future. Here is link to the
> discussion -
> http://lists.openstreetmap.org/pipermail/routing/2011-April/001127.html
> You may want to have a look there.
>
> Sorry for the delayed replies, presently, I am a bit
> occupied by college submissions. I will go through the links
> and the ideas proposed here by Daniel and Steve soon. As
> already said I guess we need to put a lot of thought in
> designing the data model, that would be easy for users to
> use, robust and flexible for different applications, and at
> the same time efficient in terms of query and processing
> time. I will try and come up with thoughts on that soon.
>
> Regarding Navteq data, the website says that only one
> data-set will be allowed to download. So, I was wondering
> which data should be preferred. Also, there are various
> data-formats that Navteq provides data in. Steve, have you
> downloaded any data which specifically has time-dependent
> edge weights?
>
> Though we will not want the module to follow Navteq
> standards, any time-dependent data would be very helpful for
> me, since I also want to try out some heuristics on that as
> part of my thesis. The work done by R. Geisberger, P.
> Sanders and others is experimented on the Germany data
> provided by PTV AG http://www.ptvag.com/company/contact/. I
> have requested them data for research purposes. Have you
> worked with their data by any chance?
>
> Regards,
>
>
> On Tue, Apr 5, 2011 at 8:05 PM, Stephen Woodbridge
> <woodbri at swoodbridge.com <mailto:woodbri at swoodbridge.com>>
> wrote:
>
> On 4/5/2011 1:37 AM, Daniel Kastl wrote:
>
> Hi Jay,
>
> As Steve said, Navteq sample data is one possibility
> ... and it's better
> than nothing ;-)
>
> Well, I think we should avoid to support a single
> data provider, because
> who tells that the format they defined several years
> ago is the most
> suitable one. It might work perfectly for Navteq and
> road networks in
> countries they are operating, but this doesn't say
> there won't be a more
> clever way to store such an information.
> I think it will be always necessary to transform
> data into a format
> pgRouting algorithms can handle. So it's OK in my
> opinion to define some
> convenient format if there isn't an existing
> standard already (which
> doesn't exist afaik).
> But Navteq is good data for testing, I agree. For
> the beginning I think
> it might be even too complex model, as Steve
> mentioned there are even
> time dependent turn restrictions.
>
>
> I think that the value in looking at Navteq is not to
> use it all, but that it is a concrete data model that
> expresses all the various routing characteristics that
> you might run into in other data sets. Navteq has been
> the basis for almost all routing solution during the
> past 10-15 years. There are now others like TeleAtlas,
> and even OSM. So look it over and use as much or as
> little as you need to get started. Designing a data
> model is very complex and you can not do it in the
> abstract - you need to know what you are modeling.
>
> As far as defining an data model that is easy for users
> to work with, keep the tables simple to understand and
> load with data. It is better to have 5 simple to work
> with tables than 1-2 complex ones. If you need to
> transform the data inside then have a preparation
> function that reads the user tables and applies them to
> the graph. So examples of user tables might be:
>
> o bus, train, ferry, airline schedules
> o live traffic data table
> o historical speed estimates by day/time (as Daniel
> mentions below)
> o transfer rules - required pre-deparature arrival time
> when transferring to a different transportation mode and
> post-scheduled arrival wait time when transferring from
> a mode. EG, must arrive at airport 2 hr before flight
> departure and allow 45 mins after arrival to collect
> baggage or longer on international flights. (this might
> not apply to your specific problem)
>
>
>
> A good place to discuss such a question might be
> also the "OSM routing"
> mailing list. In the worst case nobody will answer.
> But maybe you will
> start a long discussion as there are several people
> very interested in
> routing related topics. OSM data would be nice, if
> we could make use of
> it, but I fear that not many mappers really think about
> time-dependent attributes. Probably in Germany you
> can find such a data.
>
>
> Yes, working with OSM is another good possibility.
>
>
> I thought a bit about some possible cases for time
> dependent road networks:
>
> * In Japan a big issue for navigation software
> are so called "School
> Zones", which are areas around schools
> obviously, which are closed
> for motorized traffic at certain times in the
> morning.
> * In Europe I know about pedestrian areas for
> example, which can be
> used for delivery of goods after regular
> business hours. Or heavy
> trucks are not allowed to access roads during
> certain times.
> * Some highways/roads in Germany have a speed
> limit during night time
> * Ferry services might only operate during day
> time (so if you
> missed the last ferry, you might have to take
> a longer way)
> * In Japan they have so called VICS data
>
> (http://www.mlit.go.jp/road/ITS/conf/2006/ts20.pdf) collected from
> road sensors, which can tell the typical speed
> on roads during
> certain hours.
>
> ... and so on ...
>
>
> One last thought on loading data. I work a lot with
> Navteq and LOTS of other data sets. The one common theme
> that I come back to is that I create data loaders for
> the various data sets I work with so I can load the data
> into the database and I always end up transforming the
> data into a simpler model that is easy to work with and
> then used by whatever application I am working on.
> Sometimes I transform the data in the loader and
> sometimes I just load it raw and transform it in the
> database and then drop the raw data tables.
>
> Hope this helps,
> -Steve
>
>
> I think what pgRouting is currently missing are some
> sort of "unit
> tests" on some test network. This can be a regular
> grid with costs
> assigned, that model a certain routing case. It
> would be really
> convenient to have something like this.
>
> Daniel
>
>
> 2011/4/5 Jay Mahadeokar <jai.mahadeokar at gmail.com
> <mailto:jai.mahadeokar at gmail.com>
> <mailto:jai.mahadeokar at gmail.com
> <mailto:jai.mahadeokar at gmail.com>>>
>
> Hi,
>
> Since we will be working on time-dependent
> shortest path problem, I
> was wondering if time-dependent geographic data
> is freely available
> for research purposes. [1] states that we
> witness an increasing
> number of navigation service providers (such as
> Navteq and
> TeleAtlas) have started releasing their
> time-dependent travel-time
> datasets for road networks at high-resolution
> temporal granularity
> as fine as one sample for every five minutes.
>
> I guess that data is not freely available.
> Anyways, if you know such
> data-source can you please direct me? Besides
> this project, I am
> also working on some new heuristics for
> time-dependent shortest path
> as part of my thesis and the data would be
> really helpful for my work.
>
> Thanks.
>
> [1] http://portal.acm.org/citation.cfm?id=1869865
>
>
> On Thu, Mar 31, 2011 at 7:49 PM, Stephen Woodbridge
> <woodbri at swoodbridge.com
> <mailto:woodbri at swoodbridge.com>
> <mailto:woodbri at swoodbridge.com
> <mailto:woodbri at swoodbridge.com>>> wrote:
>
> On 3/30/2011 9:45 PM, Daniel Kastl wrote:
>
>
> float cost :=
> getEdgeCost(time, vehicle_type,
> node_from,
> node_to);
>
> or something like that.
> Where time could be NULL
> for some
> default
> behavior, or a value that
> would be used to
> figure out the cost.
> vehicle_type might be
> helpful if there are
> multiple costs to
> traverse a link based on
> say, car, carpool, bus,
> truck, walking,
> taxi, etc. This could also
> be used to implement
> the rules
> for bus
> and train lines.
>
>
> I think one of the difficulties with
> routing topic is that
> everyone
> (also myself) immediately think about
> routing in terms of
> vehicle types.
> It's the easiest example to explain
> pgRouting, but I think
> one premise
> of pgRouting is that it should work for
> any kind of network.
> Let's say
> your network would be the human nervous
> system. What is a
> vehicle there?
> Well, probably changing "vehicle_type"
> to "speed" would make
> sense, right?
>
>
> Sorry for using vehicle as the selector
> maybe "service_type"
> would be better, but the point is not the
> name, "speed" is
> equally misleading, the point is to be able
> to be able to pass a
> selector to the under lying function so that
> based on the
> selector we can compute an appropriate cost.
>
> For my vehicle routing example, I chose:
> car, carpool, bus,
> truck, walking, taxi, etc. because these
> might have different
> rules associated to them. The selector
> values would be
> appropriate to the model that you were
> working with.
>
> car vs carpool vs bus - many cities have HOV
> lanes that bus and
> carpool can use but not single occupancy
> cars. We might want to
> allocate a higher speed to those lanes vs
> the normal lanes
> during rush hours. Emergency vehicles many
> be allowed to make
> u-turns on highways that other vehicles can
> not make. Trucks
> might be banned from some streets so need to
> be costed
> appropriately, etc.
>
> If we had a live traffic feed information
> linked to segment ids
> in another table, The cost function could be
> implemented to
> check that table and if a record exists then
> use that
> information or return the standard
> information. By keeping this
> data in a separate table that is presumably
> much smaller and
> dynamic than the street records it would
> make it much easier and
> more cost effective to make dynmaic changes
> to that table and to
> hide (abstract away complexity) by using a
> cost function
> supplied to the underlying code.
>
> -Steve
>
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> --
> Regards,
> -Jay Mahadeokar
>
>
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> eMail: daniel.kastl at georepublic.de
> <mailto:daniel.kastl at georepublic.de>
> <mailto:daniel.kastl at georepublic.de
> <mailto:daniel.kastl at georepublic.de>>
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> -Jay Mahadeokar
>
>
>
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> -Jay Mahadeokar
>
>
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