[pgrouting-dev] Support for Time Constraints
Stephen Woodbridge
woodbri at swoodbridge.com
Tue Apr 5 10:35:11 EDT 2011
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>>
>
> 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>> 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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> --
> Georepublic UG & Georepublic Japan
> eMail: daniel.kastl at georepublic.de <mailto:daniel.kastl at georepublic.de>
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