Brian Good comments - and from my "NaPTAN" perspective I share your view that data improvement should be a two-way thing. I am very keen to see if we can make that work through this exercise.
I have always said that linear positioning of bus stops can be good enough if it is +/- 10m given that a bus is typically 12m long. But if it can be more precise than this, so much the better. Lateral displacement is more serious from the mapping perspective - and therefore the tolerance probably in both directions has to be set rather lower. Strangely at about the same time as you sent your message, one of my colleagues researching something completely different through the traveline journey planners, also commented on issues to do with the incorrect representation of Digbeth in NaPTAN data. My quick assessment is that neither the old nor the current coach stations have a NaPTAN record - and what has been happening without anyone realising it is that coaches have been shown on journey planners to be going to and from a particular roadside stop in the area of the old coach station. I have asked someone to investigate this and get it resolved in NaPTAN in the near future. I would be able to comment more about the missing data and other aspect which you and others draw to the list's attention if I could have a copy of the NaPTAN data that has been put through the import process - can you (or someone else on the list) either point me to where I can find that specific data set . or can send me a copy of the specific data that has been imported? Best wishes Roger _____ From: [email protected] [mailto:[email protected]] On Behalf Of Brian Prangle Sent: 01 April 2009 13:41 To: [email protected]; [email protected] Subject: [Talk-transit] 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. It's 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. It's 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 can't 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. That's 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 - that's 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 we're OK by surveying and tagging the physical one with Andy's 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 - I'm of the view that as long the bus stop has more or less the right relationships to its surroundings then that's 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 doesn't exist? 11. Can't find any nodes for taxi ranks - not imported or doesn't exist for Birmingham or I'm not looking hard enough? 12. For the few nodes where I've estimated the fit between OSM and NaPTAN to be "good enough" I've 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.
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