Geospatial Data Analysis and Simulation
Header

MapTube Topical Maps

February 20th, 2012 | Posted by Richard Milton in Uncategorized - (0 Comments)

It is four years today since MapTube was launched at the Barbican and to mark this event, I’ve made some changes to how the home page displays. This is a bit of an experiment, but I’ve tried to make the home page display topical data by using RSS feeds from the BBC News page, the Guardian and our own CASA blog aggregator. The basic method is to construct a list of keywords and frequencies from the RSS feeds, removing any words on a “stop words” list like “a”, “and”, “or” etc. Then a network graph of MapTube’s maps is constructed where each vertex is a map which is linked by edges made from where maps share keywords. So, for example, all the “London” maps form a fully connected group. This is similar to my previous post on using “Force Directed Graphs for Visualisation of Search Results”: http://talisman.blogweb.casa.ucl.ac.uk/2012/01/23/force-directed-graphs-for-visualisation-of-search-results/

Network Graph of MapTube London Maps

Once the connections between the maps has been calculated, each vertex is visited in turn and assigned a topicality value based on the RSS word frequency of all the map’s matching keywords. This weight is then propagated through the network via any connected edges up to a distance of 2 links from the parent vertex, with the weight reduced by a factor of 1/(r^2), where “r” is the number of vertices traversed. I did experiment with how many links from the parent vertex to travel, but found that 1 or 2 links from the parent gave the best results. Any further than this and it just ends up giving weight to the maps with the highest number of connections.

As I stated at the beginning, this is still very much an experiment and I’ve deliberately built the system with enough degrees of freedom to allow for some tinkering with the algorithm. I can control which feeds we mine for the topical keywords, the stop words list can be edited (I had to put “us” back in as we have a lot of United States maps) and I also have the ability to add my own keyword weights. At the moment I’ve artificially inflated the real-time tube locations map to get it onto the front page along with our most popular map of the London Underground tube station locations, which is now three years old. The first run of the system on the live server produced high values for a lot of the air quality maps, which was an interesting result.

The biggest criticism I had of MapTube was that the home page always displayed the most popular maps, sorted by the number of hits. This meant that the most popular maps stayed on the front page by virtue of people always clicking on the top ones. We did try showing the most recently added maps for a while, but that didn’t work as lots of test maps get uploaded with no data on them. Hopefully, as this new topical maps system evolves, we should see MapTube as a much more dynamic source of geographical information.

One final point, but by knowing what data we have on MapTube that’s topical, we also know what’s topical that we don’t have and should perhaps try to track down and upload. This approach would form a closed loop geographic information system.

National Rail Train Locations

February 15th, 2012 | Posted by Richard Milton in Uncategorized - (0 Comments)

The purpose of my previous post on the TransXChange timetable data was to make it possible to track National Rail trains in real time. Due to the large number of stations making up the network and the fact that you can’t obtain information for a whole line in one go, the only viable option is to use timetable data. The other limiting factor is the lack of any kind of unique train identifier on the National Rail website (see: http://ojp.nationalrail.co.uk/service/ldbboard/dep/EUS ).

The preliminary results are shown below:

Trains going into or out of Waterloo for 16:42 on a weekday

The technique is quite simple and involves making requests to the National Rail website to probe the current positions of trains. We first ask where the trains should be at the current point in time based on the timetable. Then, we probe the running information for the stations just ahead of where the trains should be. Tested using the whole of the Greater London network, only 319 unique station requests were required to determine train positions out of a total of 2,575 stations. This number can be reduced even further as we only need to hit on a single station ahead of the train in order to find out whether it’s on time. The position can always be worked out from the timetable by asking where it should be on its route at the time now minus the late minutes.

Once all the data for the departure boards has been collected, the next stage is to match up trains to departure details for stations based on the passing points extracted from the TransXChange timetable. This links a train to the running service which tells us all the stopping points and times on its route, along with a unique route code. This unique route code is used to identify the same train on different departure boards so we can use the best position information available, in other words, the departure board that it is approaching next.

An interesting question is what happens if there is enough of a disruption to the services to make the timetable useless? In this situation, the concept of whether a train is late is meaningless, but we still have a system which can probe the departure boards and match trains using the runtimes between stations. Certain network geometries make it impossible to match trains accurately without timetable data if the destination is shared between two routes. For example, a “Y” section where two trains with the same destination code merge onto one line. Another complicating factor is the circular route, where trains all start at Waterloo and end up at Waterloo again.

For a project on transport data I needed access to the National Rail timetables to calculate passing points for trains at every station. The National Public Transport Data Repository (NPTDR) TransXChange data is available for download on the data.gov.uk site, but it’s easier to download from the Department for Transport site: http://data.dft.gov.uk/NPTDR/index.html

TransXChange is an XML format which supercedes the old “CIF” format files which were in a coded ASCII format. Once I had downloaded the October 2010 data, which is the latest available as this is only a yearly snapshot done in October, I then had to write some software to calculate all the passing points.

I’m using C#, so the first thing I did was to autogenerate a class matching the TransXChange schema. All the necessary schema files can be found at the following link: http://www.transxchange.org.uk/schema/schemas.htm My TransXChange data is using the 2.1 schema, so I downloaded that version.

Next, I used the following command to create a class for the schema using Visual Studio’s “xsd” tool:


xsd.exe -c -l:c# -n:TransXChangeXML
TransXChange_general.xsd TransXChange_common.xsd TransXChange_types.xsd TransXChange_registration.xsd
apd\AddressTypes-v1-3.xsd apd\BS7666-v1-3.xsd apd\CitizenIdentificationTypes-v1-3.xsd
apd\CommonSimpleTypes-v1-3.xsd apd\ContactTypes-v1-3.xsd apd\PersonalDetailsTypes-v1-3.xsd apd\PersonDescriptiveTypes-v1-0.xsd

This generated a C# class called TransXChangeXML, although I do get lots of warnings about multiple definitions which I ignored.

The next part involved deserialising the “ATCO_490_TRAIN.TXC” file into my class. I’m using area 490 which is Greater London, so I had to unpack the relevant zip files from the TransXChange download.

After reading the TransXChange manual for some time and some experimentation, I worked out that the method for calcualting passing points is as follows:

FOR EVERY “<Service>”

Get the JourneyPattern id from inside “<StandardService>”, which is the journey reference code (e.g. “JP8755”) and also the sequence code from the “<JourneyPatternSectionRefs>” (e.g. “SEQ12SEC11”)

Lookup the “<JourneyPatternRef>” code in the “<VehicleJourneys>/<VehicleJourney>” section. This gives us an absolute departure time and a list of “<JourneyPatternTimingLinkRef>” references (e.g. “SEC162POS95”) containing runtimes and wait times for the “from” and “to” links. These sequence positions are merged with ones from “<JourneyPatternSections>” looked up using the “SEQ_SEC_” reference from earlier. The vehicle timing links have preference over the journey pattern timing links.

FOR EVERY TimingLink from previous stage

Link Arrival Time = Previous Link Departure Time + RunTime

Link Departure Time = Arrival Time + Wait Time from end of previous link (“TO”)

The code for this is copied below:


//read TransXChange file
XmlReaderSettings settings = new XmlReaderSettings();
settings.ConformanceLevel = ConformanceLevel.Fragment;
settings.IgnoreWhitespace = true;
settings.IgnoreComments = true;

using (XmlReader reader = XmlReader.Create(Filename, settings))
{
    XmlSerializer SerializerObj = new XmlSerializer(typeof(TransXChangeXML.TransXChange));
    TransXChangeXML.TransXChange TXC = (TransXChangeXML.TransXChange)SerializerObj.Deserialize(reader);

    //Build a JourneyPattern index by the section cdoe
    Dictionary JPS = new Dictionary();
    foreach (TransXChangeXML.JourneyPatternSectionStructure JourneyPattern in TXC.JourneyPatternSections)
    {
        JPS.Add(JourneyPattern.id, JourneyPattern);
    }

    //build an index of vehicle journeys by the JP ref code so that we can look them up easily
    Dictionary VehicleJourneyByJPRef = new Dictionary();
    //VehicleJourneys have departure times
    foreach (TransXChangeXML.VehicleJourneyStructure VehicleJourney in TXC.VehicleJourneys.VehicleJourney)
    {
        string VJourneyCode = VehicleJourney.VehicleJourneyCode;
        DateTime VDepartureTime = VehicleJourney.DepartureTime;
        string VOperatorRef = VehicleJourney.OperatorRef.Value; //e.g. SW=SW TRAINS

        string JPRef = "";
        if (VehicleJourney.Item is TransXChangeXML.VehicleJourneyRefStructure) JPRef = (VehicleJourney.Item as string);
        else if (VehicleJourney.Item!=null) JPRef = (VehicleJourney.Item as TransXChangeXML.JourneyPatternRefStructure).Value; //this must be an xsd error? All this just to get the JP code?

        //TODO: need an array of the duplicates indexed by JPRef
        if (!string.IsNullOrEmpty(JPRef))
        {
            if (VehicleJourneyByJPRef.ContainsKey(JPRef))
            {
                //System.Diagnostics.Debug.WriteLine("Duplicate key: " + JPRef);
            }
            else
                VehicleJourneyByJPRef.Add(JPRef, VehicleJourney);
        }
    }

    //Now go through all the services, linking them up to the VehicleJourneys via their JP reference. The VehicleJourney contains the
    //parent sequence of stops which is then overridden by any JourneyPatternSectionRefs contained in the JourneyPattern.

    //Services only have relative timings on them, but link to VehicleJourneys through the JP ref, which gives us absolute times
    foreach (TransXChangeXML.ServiceStructure Service in TXC.Services)
    {
        TransXChangeXML.StandardServiceStructure StandardService = Service.StandardService;
        string SDDestination = StandardService.Destination.Value;
        string SDOrigin = StandardService.Origin.Value;
        //The parent service destination and origin only seem to be to do with the grouping and not something you would actually display
        //System.Diagnostics.Debug.WriteLine("Service: Destination = " + SDDestination + " Origin = "+SDOrigin);

        foreach (TransXChangeXML.JourneyPatternStructure JP in StandardService.JourneyPattern)
        {
            string JPRef = JP.id; //this is the JP number
            if (JPRef == "JP8755") //This is Shepperton
            {
                string DestinationDisplay = JP.DestinationDisplay.Value; //this overrides the StandardService Destination
                //lookup the journey using the JP code, which gives us a departure time and the section links which can be overridden
                TransXChangeXML.VehicleJourneyStructure VehicleJourney = VehicleJourneyByJPRef[JPRef];
                DateTime DepartureTime = VehicleJourney.DepartureTime;

                //make a list of the timing link overrides from the VehicleJourneys which also gives us waiting times and additional runtimes
                Dictionary VTimingLinks = new Dictionary();
                if (VehicleJourney.VehicleJourneyTimingLink != null)
                {
                    foreach (TransXChangeXML.VehicleJourneyTimingLinkStructure TimingLink in VehicleJourney.VehicleJourneyTimingLink)
                    {
                        VTimingLinks.Add(TimingLink.JourneyPatternTimingLinkRef.Value, TimingLink);
                    }
                }

                //get journey pattern timing links from SEQ SEC ref number
                System.Diagnostics.Debug.WriteLine("Departure Time: "+DepartureTime + " Destination display: " + DestinationDisplay + " JP id=" + JP.id);
                //now traverse the Journey accumulating a TimeDelta at each stop relative to the VehicleJourney Departure Time
                TimeSpan TimeDelta = new TimeSpan();
                TimeSpan FromWaitTime = new TimeSpan();
                TimeSpan ToWaitTime = new TimeSpan();
                foreach (TransXChangeXML.JourneyPatternSectionRefStructure SeqSecRef in JP.JourneyPatternSectionRefs)
                {
                    System.Diagnostics.Debug.WriteLine("REF: " + SeqSecRef.Value);
                    TransXChangeXML.JourneyPatternSectionStructure JourneyPattern = JPS[SeqSecRef.Value]; //lookup JourneyPattern using SEQ SEC ref number
                    foreach (TransXChangeXML.JourneyPatternTimingLinkStructure TimingLink in JourneyPattern.JourneyPatternTimingLink)
                    {
                        //todo: need activity in here...
                        TimeSpan RunTime = ParseTime(TimingLink.RunTime);

                        FromWaitTime = ToWaitTime; //weird - wait time on end of last segment rolled around to start of this segment
                        ToWaitTime = new TimeSpan();
                        if (!string.IsNullOrEmpty(TimingLink.To.WaitTime)) ToWaitTime = ParseTime(TimingLink.To.WaitTime);

                        if (VTimingLinks.ContainsKey(TimingLink.id))
                        {
                            TransXChangeXML.VehicleJourneyTimingLinkStructure VTimingLink = VTimingLinks[TimingLink.id]; //VehicleTimingLink lookup
                            if (!string.IsNullOrEmpty(VTimingLink.RunTime)) RunTime = ParseTime(VTimingLink.RunTime);
                            if ((VTimingLink.To != null) && (!string.IsNullOrEmpty(VTimingLink.To.WaitTime)))
                            {
                                ToWaitTime = ParseTime(VTimingLink.To.WaitTime);
                            }
                        }

                        System.Diagnostics.Debug.WriteLine("Arrive: " + (DepartureTime+TimeDelta) + " Depart: " + (DepartureTime+TimeDelta+FromWaitTime)
                            + " " + TimingLink.id + " " + TimingLink.From.StopPointRef.Value + " " + TimingLink.To.StopPointRef.Value
                            +" Runtime="+RunTime+" FromWaitTime="+FromWaitTime+" ToWaitTime="+ToWaitTime);
                        TimeDelta = TimeDelta + FromWaitTime + RunTime;
                    }
                }
                System.Diagnostics.Debug.WriteLine("Final arrival: "+(DepartureTime+TimeDelta));

            }
        }
    }
}

I’ve limited the code to only produce the passing points for a single service, “JP8755”, which is a Waterloo to Shepperton service. This produces the following output:

Departure Time: 01/01/0001 05:12:00 Destination display: Shepperton Rail Station JP id=JP8755
REF: SEQ12SEC11
Arrive: 01/01/0001 05:12:00 Depart: 01/01/0001 05:12:00 SEQ12POS88 9100WATRLMN 9100VAUXHLM Runtime=00:03:00 FromWaitTime=00:00:00 ToWaitTime=00:01:00
Arrive: 01/01/0001 05:15:00 Depart: 01/01/0001 05:16:00 SEQ12POS89 9100VAUXHLM 9100CLPHMJM Runtime=00:04:00 FromWaitTime=00:01:00 ToWaitTime=00:01:00
Arrive: 01/01/0001 05:20:00 Depart: 01/01/0001 05:21:00 SEQ12POS90 9100CLPHMJM 9100ERLFLD Runtime=00:03:00 FromWaitTime=00:01:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:24:00 Depart: 01/01/0001 05:24:00 SEQ12POS91 9100ERLFLD 9100WDON Runtime=00:04:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:28:00 Depart: 01/01/0001 05:28:00 SEQ12POS92 9100WDON 9100RAYNSPK Runtime=00:03:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:31:00 Depart: 01/01/0001 05:31:00 SEQ12POS93 9100RAYNSPK 9100NEWMLDN Runtime=00:03:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:34:00 Depart: 01/01/0001 05:34:00 SEQ12POS94 9100NEWMLDN 9100NRBITON Runtime=00:03:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:37:00 Depart: 01/01/0001 05:37:00 SEQ12POS95 9100NRBITON 9100KGSTON Runtime=00:03:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:40:00 Depart: 01/01/0001 05:40:00 SEQ12POS96 9100KGSTON 9100HAMWICK Runtime=00:02:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:42:00 Depart: 01/01/0001 05:42:00 SEQ12POS97 9100HAMWICK 9100TEDNGTN Runtime=00:03:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:45:00 Depart: 01/01/0001 05:45:00 SEQ12POS98 9100TEDNGTN 9100FULWELL Runtime=00:04:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:49:00 Depart: 01/01/0001 05:49:00 SEQ12POS99 9100FULWELL 9100HAMPTON Runtime=00:04:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:53:00 Depart: 01/01/0001 05:53:00 SEQ12POS100 9100HAMPTON 9100KMPTNPK Runtime=00:03:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:56:00 Depart: 01/01/0001 05:56:00 SEQ12POS101 9100KMPTNPK 9100SUNBURY Runtime=00:02:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 05:58:00 Depart: 01/01/0001 05:58:00 SEQ12POS102 9100SUNBURY 9100UHALIFD Runtime=00:02:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Arrive: 01/01/0001 06:00:00 Depart: 01/01/0001 06:00:00 SEQ12POS103 9100UHALIFD 9100SHEPRTN Runtime=00:05:00 FromWaitTime=00:00:00 ToWaitTime=00:00:00
Final arrival: 01/01/0001 06:05:00

Comparing this with the South West Trains timetable for the service, I can check that all the arrival and departure times are correct. It’s worth pointing out that, while this data is an October 2010 timetable, the current timetable in operation hasn’t changed in that time. This code should also be treated with caution as it hasn’t been rigorously tested. As can be seen from some of the comments, there are parts of the TransXChange schema that I’ve ignored for the sake of simplicity, for example, the activity at the stop and whether it’s a “Dead Run”.

Now that I have a list of passing points for every station in Greater London, I can use the information to build a real-time train tracking system.