Roger Slevin [mailto:ro...@slevin.plus.com] wrote: >Sent: 01 April 2009 8:18 PM >To: 'Andy Robinson (blackadder-lists)'; 'Brian Prangle'; Talk-gb- >westmidla...@openstreetmap.org; talk-transit@openstreetmap.org >Subject: RE: [Talk-transit] [Talk-gb-westmidlands] NaPTAN bus stop >databaseimport - some moreobservations > >Andy > >Useful assessment of a small group of records - thanks for making it >available. > >I looked at the first one of the ones you said was not represented on the >road ... looking at the NaPTAN data the stop is classed as "CUS" which >means >"Custom and practice" - or in other words, "unmarked". You comment that it >appeared to be unused - and my quick check of the West Midlands traveline >journey planner seems to confirm that this is likely to be the case. I >think it would have been used at some time in the period since traveline >began in 2000 ... but in NaPTAN the ACTive status of a record does NOT mean >it is in use, it simply means that it is available to be used. This is >fundamental to NaPTAN which is only a location database - it is not >influenced directly by the existence of services. Of course it would be >possible for Centro to designate the stop as inactive ... but there is no >obligation on them to do so, and most authorities will only do that in >situations where a stop is taken out of service permanently (maybe for >safety reasons, or changes in adjacent development). > >I hope this is a useful insight into the context of at least some of your >comments.
It is, thanks. It reinforces the need to separate out within OSM that data which is current and relevant and that which is fanciful. The latter can stay in but needs to be properly flagged as "inactive". Since OSM is a wiki anyone can reactivate a node at a later date. BTW, Thomas has just imported West Bromwich (not many stops) ready for our mapping party at the weekend. We will discuss the rest of the west mids at our social tomorrow evening. Cheers Andy > >Best wishes > >Roger > > >-----Original Message----- >From: talk-transit-boun...@openstreetmap.org >[mailto:talk-transit-boun...@openstreetmap.org] On Behalf Of Andy Robinson >(blackadder-lists) >Sent: 01 April 2009 19:40 >To: 'Brian Prangle'; talk-gb-westmidla...@openstreetmap.org; >talk-transit@openstreetmap.org >Subject: Re: [Talk-transit] [Talk-gb-westmidlands] NaPTAN bus stop >databaseimport - some moreobservations > >As promised my review of a further 50 bus stops in Sutton Coldfield. See >the >linked PDF [1] for full analysis. > >50 locations evaluated in Sutton Coldfield. All stops except one in the >NaPTan database and the one that wasn't is an unused shelter in a row of >shelters in the centre of town so probably isn't in the NaPTAN dataset >anyway. > >Of the remaining 49, 13 (27%) have no physical presence on the ground and >in >most case have never been used as a stop as far as I know. > >The average positional error from my survey was 13.7m with a maximum of 84m >and a minimum of 1.6m. One third were within 5m. The standard deviation was >16.84m. > >The majority of stops were logically positioned on the correct side of the >road and where it was close I checked the road alignment and adjusted it to >the GPS traces where appropriate. A small number of NaPTAN nodes were not >in >their logical positions, eg both stops of a pair on the same side of the >street. The largest displacement values were all longitudinal displacements >along the street. > >A question arises what to tag a NaPTAN stop that is not present on the >ground. I've used for now physically_present=no. These stops also don't >currently carry a highway=bus_stop tag. > >Cheers > >Andy > >[1] http://ajr.hopto.org/osm/NaPTAN.pdf > > >>-----Original Message----- >>From: talk-gb-westmidlands-boun...@openstreetmap.org [mailto:talk-gb- >>westmidlands-boun...@openstreetmap.org] On Behalf Of Brian Prangle >>Sent: 01 April 2009 1:41 PM >>To: talk-gb-westmidla...@openstreetmap.org; talk-transit@openstreetmap.org >>Subject: [Talk-gb-westmidlands] NaPTAN bus stop database import - some >>moreobservations >> >>Some more views and observations on the NaPTAN data import in Birmingham: >>1. It serves as a great QA on OSM data and shows that in the City Centre >>where we have not been able to get decent GPS traces more accuracy is >>needed so the potential of obtaining aerial photography is great. >>2. Its a great impetus to resurvey streets where earlier work (potentially >>inaccurate from NPE tracing, older GPS devices, less points collected, >>inexperience, not realising that roads have a width greater than the >>rendered line so placing bus stops too close to the road etc.) can be >>improved. >>3. Its also a great impetus to improve practice on surveying bus stops and >>be much more precise and comprehensive also a stimulus to edit all those >>old bus stops where we placed them as a node on the way rather than to the >>side of ways which is our current practice. >>4. QA works both ways and our surveys should help to improve NaPTAN data. >>5. As an exercise(excuse the pun!) I cycled from Acocks Green to Moseley >>and back this morning along the No 1 bus route and surveyed 47 bus stops >>each time standing at the pole(leaning against it you cant get closer than >>that!) or underneath the plate at a shelter: 4 bus stops coincided within >>3-4 m; 17 were good enough coinciding <8-10m. Thats approx 45%. The rest >>were out by anything up to 90m or were just missing. >>6. I think either the pole where there is no shelter or the bus stop plate >>at a shelter should be what we survey thats where the identification of >>what we survey is located >>7. Where a physical stop on one side of the road doubles up for one on the >>other side also I think were OK by surveying and tagging the physical one >>with Andys suggestion of a tag opposite=yes. The NaPTAN untagged node on >>the other side can be left in place to indicate the logical relationship. >>8. I like the idea of tagging where the bus stop is set back in a lay-by >>from the road which might account for some NaPTAN nodes being some >distance >>from the road >>9. For our purposes good enough is probably sufficient rather than precise >>positional detail Im of the view that as long the bus stop has more or >less >>the right relationships to its surroundings then thats OK. >>10. Surprised that there is no data for either the closed Digbeth Coach >>Station which is being rebuilt or the temporary replacement nearby. I >>thought we were importing off-street bus stops? Perhaps the NaPTAN data >>doesnt exist? >>11. Cant find any nodes for taxi ranks not imported or doesnt exist for >>Birmingham or Im not looking hard enough? >>12. For the few nodes where Ive estimated the fit between OSM and NaPTAN >to >>be good enough Ive merged the nodes deleting the unverified tag and >editing >>source tag to v=naptan_import;survey >>13. Verifying the data is going to be a long, slow process with a lot of >>resurveying needed. > > >_______________________________________________ >Talk-transit mailing list >Talk-transit@openstreetmap.org >http://lists.openstreetmap.org/listinfo/talk-transit > _______________________________________________ Talk-transit mailing list Talk-transit@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-transit
