[Talk-gb-westmidlands] [Talk-transit] NaPTAN bus stop database import - some moreobservations

[Roger Slevin]

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: talk-transit-bounces at openstreetmap.org
[mailto:talk-transit-bounces at openstreetmap.org] On Behalf Of Brian Prangle
Sent: 01 April 2009 13:41
To: Talk-gb-westmidlands at openstreetmap.org; talk-transit at openstreetmap.org
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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