[Talk-gb-westmidlands] [Talk-transit] Naptan alignment

[Andy Robinson (blackadder-lists)]

Peter Miller [mailto:petermiller63 at googlemail.com] On Behalf Of Peter
Miller wrote:
>Sent: 31 March 2009 6:16 PM
>To: Andy Robinson (blackadder-lists)
>Cc: 'Brian Prangle'; Talk-gb-westmidlands at openstreetmap.org; talk-
>transit at openstreetmap.org; 'Thomas Wood'
>Subject: Re: [Talk-transit] [Talk-gb-westmidlands] Naptan alignment
>
>
>On 31 Mar 2009, at 13:23, Andy Robinson (blackadder-lists) wrote:
>
>> I've already started correcting data like this. I too have noted
>> that some
>> stops are not correctly positioned in relation to the road they are
>> on.
>> Where we only have a single trace along a road they could be correct
>> but the
>> ones I looked at last night where we have plenty of traces (main
>> road) were
>> in some cases either too far back or too close to the centreline of
>> the
>> road. I also fond some possible referencing errors for bus stop
>> pairs on
>> either side of the road but need to resurvey as a double check.
>>
>> As of my mapping session this morning I'm taking my bike right up to
>> the
>> stop and taking the photo from directly under the sign. That should
>> help see
>> what sort of positional errors exist in the data. The only problem
>> is that
>> I'm mapping Walsall and so need more imported data before I'll
>> know ;-)
>>
>
>Import looks good.  A few points:
>
>1) The bearing is useful to ensure that the stop is put on the correct
>side of the street) . Normally the stop will already be on the correct
>side using the lat-long, but if the stop in misplaced by poor GPS then
>we could place it on the wrong side. I did find one that was on the
>wrong side of the street in the OSM environment using the bearing from
>the official data.

Havent seen much of a problem of this as yet but your point noted.
>
>2) Some Naptan records seem to be missing in OSM. In the case where
>there is already a bus stop in the right place is the Naptan record
>just being deleted in the review pass? If so then important data for
>maintenance is being lost. I would suggest that the two records are
>merged to ensure that there are NaPTAN codes for every stop.

I'm not deleting any NaPTAN data but instead merging my data onto the NaPTAN
nodes and if necessary moving the final node a bit where it needs it. I
agree that we don't want to loose any of the imported data.

>
>3) I find it interesting that in some places OSM has bus stops that
>are not in NaPTAN, that might be because they have been removed
>recently or be an omission in NaPTAN.

I've spotted several too. Definitely on the ground so looks like the NaPTAN
data is missing or for some reason they don't have a "Birmingham" value
which Edgemaster used for the initial filter.

>
>4) I notice that sometimes the NaPTAN stop and the OSM one are some
>significant distance apart which begs the question about which one is
>right.

I've noted this too. I'm going to do a precise check in my area to see what
accuracy I place on the NaPTAN positions. I've also from today started to be
more precise about getting the position of bus stops when I survey. I should
be within 0.5m +/- the GPS accuracy (generally sub 5m with this Legend HCx I
use).

Cheers

Andy

>
>
>Anyway, it looks like the detective work is now starts! Great work.
>
>
>
>Regards,
>
>
>
>> Cheers
>>
>> Andy
>>
>>> -----Original Message-----
>>> From: talk-gb-westmidlands-bounces at openstreetmap.org [mailto:talk-gb-
>>> westmidlands-bounces at openstreetmap.org] On Behalf Of Brian Prangle
>>> Sent: 31 March 2009 9:46 AM
>>> To: Talk-gb-westmidlands at openstreetmap.org; talk-
>transit at openstreetmap.org
>>> ;
>>> 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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