On 31 Mar 2009, at 23:43, Andy Robinson (blackadder-lists) wrote:
Roger Slevin [mailto:[email protected]] wrote:
Sent: 31 March 2009 11:20 PM
To: 'Andy Robinson (blackadder-lists)'; 'Brian Prangle'; Talk-gb-
[email protected]; [email protected];
'Thomas
Wood'
Subject: RE: [Talk-transit] [Talk-gb-westmidlands] Naptan alignment
Andy
"Custom and Practice" stops - that is stops which are not
physically marked
- are a common feature in many parts of the country ... less so
within
Metropolitan areas than in rural ones. And many are not "signed in
one
direction to represent both directions" - they are without any
sign. These
unmarked stops are stop type CUS in NaPTAN. I appreciate that their
representation on a map might be conceptually challenging ... but
they are
essential points as far as bus passengers are concerned!
I have no problem representing them on a map and indeed the whole
concept is
fine. Our challenge is one of verification. We essentially only put
data in
OSM that is physically there on the ground. However at least these
stops
have the "CUS" tag so it should be possible to verify that busses
stop at
the location and the evidence on the ground might then be the pile
of fag
ends in the gutter ;-)
I would have thought that in the UK the 'verification' of a customary
stop could initially be that the data is within NaPTAN and that it
doesn't seem unreasonable (ie it is not on a one-way street).
Cigarette ends and people standing around looking up the road might
corroborate that information but I suggest that they are not necessary
where NaPTAN has provided data.
We should note that this import is getting attention from
professionals and that in the UK/ Transmodel because it is seen as
'The' essential link between the timetables and the physical world and
they have seen and discussed a lot of unusual situations that need to
be accommodated in the past 10 years. I would suggest therefore that
we see if we can accommodate their requirements.
Could I suggest that normally a bus-stop will be a pole, a shelter, a
customary stop or a combination of a pole/shelter combination where
the elements are close together and where the bus stops near that node
and the stop can be modelled using a single node at that point with
the appropriate tags. However, In situations where the stopping
position (as indicated by a lay-by, paint on the road or a section of
raised curb) is different from the position of the shelter then the
bus stop should be shown at the point where people enter the vehicle
and that the shelter/pole should be mapped as a separate feature?
There are probably a couple of reasons that the professional community
is interested in this detail. Firstly with GPS tracked buses it is
importation to know if the bus is crawling towards the bus stop
through traffic and should be shown on the electronic sign as 'due' or
if it is at the bus stop, or if it is crawling away from the stop
through traffic and should not be displayed. Also... with GPS tracked
buses the time that it 'arrived' at the stop and 'left' the stop are
both recorded for management purposes and bus companies can be fined
£100K+ for failing to meet required timings so this is a matter of
great importance to them! The other reason to be concerned about this
is for blind/partially sighted.
I note that there is no aerial photography for Birmingham from yahoo.
I also note from http://sautter.com/map that the alignment for roads
in Bham on OSM is out by significant distances in some places when
compared to TeleAtlas data on Google maps and that the TeleAtlas data
aligns with the aerial photography on Google so it looks as though
some roads in central Bham on OSM are slightly out for understandable
reasons. This means that in some cases we will will need to move
NaPTAN stops to the 'wrong' geolocation to get them to match correctly
with the roads which is a shame. In other cases it is clear from
looking at NaPTAN data on top of google aerial photography that the
NaPTAN stops are already in the wrong position - sometimes the stops
are offset back from the road and on other occasions they are
incorrectly positioned along the road.
So.... what is we were able to find someone to pay for rectified
Digital Globe satellite photography for Bham to allow the detailed
street geometry for the area in OSM to be corrected? The cost of this
for the 700 sq km that makes up most of Bham would be able £6K. If
that would be useful to OSM then possibly someone in the local
transport authority or DfT could be persuaded to provide the necessary
funds to purchase this, however the first question is if that would be
appreciated and used by the local OSM community. I certainly found it
useful in Ipswich to use yahoo aerial photography to adjust my
physical survey and spot missing streets in my initial survey - and
OSM and TeleAtlas are now much closed together for road alignment in
Ipswich using sautter as a result. This seems to be the only practical
and legal way to get the data right for NaPTAN and for OSM in Bham.
By way of reassurance, yes you can use the DG photography to derive
mapping, but you can't use the DG photography within public facing
products itself for that price. We used this approach for the Gaza
project and it worked fine. Here are some more details:
https://www.swiftpage6.com/speasapage.aspx?X=2Y0QTEPLHQPGU9KC00Z5WD
Regards,
Peter
Cheers
Andy
Roger
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Andy
Robinson
(blackadder-lists)
Sent: 31 March 2009 23:11
To: 'Brian Prangle'; [email protected];
[email protected]; 'Thomas Wood'
Subject: Re: [Talk-transit] [Talk-gb-westmidlands] Naptan alignment
Using http://sautter.com/map I did a comparison of the precisely
positioned
stops I mapped this morning in the Aldridge area. Assuming Google
has the
locations the same as the NaPTAN data then I would say about one in 5
NaPTAN
stops has something wrong with the location. Mostly a stop is
displaced
along the street. These errors are as much as 30m.
One interesting question relates to stops on the ground that exist
only on
one side of the street but state they also pickup/drop on the
opposite side
of the street. The NapTan data contains two stops when on the
ground there
is only one physical (pole or shelter). In general the NaPTAN data
appears
to show the stops staggered on either side of the street when in
practice
passengers are going to wait opposite the bus stop sign/shelter. At
the
moment I'm mapping these with one node and an opposite=yes tag on
them.
There is no way to map the stop on the opposite side as it doesn't
physically exist. So what to do about the NaPTAN data in this case.
Cheers
Andy
-----Original Message-----
From: [email protected] [mailto:talk-
gb-
[email protected]] On Behalf Of Brian Prangle
Sent: 31 March 2009 9:46 AM
To: [email protected]; talk-
[email protected];
Thomas Wood
Subject: [Talk-gb-westmidlands] Naptan alignment
Thomas
I've also looked at Google maps and their alignment is off too in
exactly
the same way ours is in areas I know well and have surveyed, so I
guess
it's down to the NaPTAN data. There are examples where I know the
bus
stops
are in a row along the street (Corporation Street and Acocks Green
Village
for example) but NapTAN has one or two skewed from the line by
several
metres. Currently I favour correcting the NapTAN data to what we
know on
the ground, but until a consensus emerges I'm laying off the urge to
correct it.
Regards
Brian
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