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

[Peter Miller]

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.

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.

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.

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.


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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