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

Peter Miller peter.miller at itoworld.com
Wed Apr 1 10:40:53 BST 2009 

On 1 Apr 2009, at 09:42, Andy Robinson (blackadder-lists) wrote:
>
>
> 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?
>
> That’s probably not going to happen for the foreseeable future. When  
> mapping
> we locate and tag what we can see on the ground. If someone in the  
> future
> wants to be pedantic and sit and wait to see the location that buses  
> stop as
> a further verification that’s fine, but that’s not a priority for  
> completing
> basic level mapping. However I would think the best approach for  
> this would
> be to get the trace data from the bus operator or from riding the  
> route to
> evaluate the differences between stop signage position and setting  
> down
> position and see if further work is needed. I suspect that if it's  
> within 5m
> or so (and most will be) its really not worth the effort.
>

To be clear, the only times you should place the bus stop somewhere  
else than where the pole/shelter is where there *is* something on the  
ground such as a lay-by, paint on the road or a raised kerb to  
indicate the need. In situations where this is the case then that  
point should be tagged as 'highway=bus_stop, and highway=bus_bay' and  
the shelter should be tagged as amenity=bus-shelter but should not be  
tagged bus-stop.

>>
> Any aerial imagery would be great provided it's properly rectified.  
> The
> Yahoo imagery in some towns is as much as 30m displaced so you can't  
> be sure
> that roads will be in the right position. My recent experience using  
> a high
> sensitivity GPS receiver at 1 sec recording interval produces very  
> good
> correlation. Just check out Walsall Wood, Rushall, Shelfield or the  
> east,
> south and west of Walsall outside the ringroad. Elsewhere the most  
> likely
> reason for poor correlation is a mixture of older GPS use and a  
> sampling
> rate on the GPS set to automatic or a long distance/time interval.  
> This
> results in loss of road shape quite quickly. Outside the Birmingham  
> inner
> ring road aerial imagery probably isn’t necessary if high sensitivity
> receivers are used because we need to resurvey bus stops anyway and  
> we'll
> therefore get more traces. I suspect even now if we pull up traces  
> for roads
> that were mapped a long time ago then we can tweak the road  
> alignment to
> better fit the increased volume of trace data.
>
> Personally I prefer not to use aerial imagery for the first survey  
> pass,
> beyond that though it's invaluable for doing all the other cool  
> things like
> adding buildings and landuse areas properly as well as tweaking all  
> objects
> that haven’t been precisely positioned, including bus stops if they  
> are
> discernable (shelters should be). Others will probably feel the  
> opposite to
> me in that it enables them to take out a printed map which can then be
> annotated to gather all the additional data, it’s a matter of  
> surveying
> style and tools available. In terms of getting new participation in  
> OSM,
> aerial imagery lowers the barrier and allows a lot more people to  
> add a lot
> more data which we want to encourage, thus I'm very much for obtaining
> imagery if we can.
>

Ok, so what I am hearing is that you would like aerial photography as  
long as it is good and well rectified. Is this the general view? If so  
then we should ask for it and see what happens. As you say the amount  
of money involved is peanuts compared to other costs of running a bus  
service or running a transport authorit

Regards,



Peter
> Cheers
>
> Andy
>
>>
>> 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: talk-transit-bounces at openstreetmap.org
>>
>>
>> 		[mailto:talk-transit-bounces at openstreetmap.org] On Behalf Of
>> Andy Robinson
>>
>>
>> 		(blackadder-lists)
>>
>>
>> 		Sent: 31 March 2009 23:11
>>
>>
>> 		To: 'Brian Prangle'; Talk-gb-westmidlands at openstreetmap.org;
>>
>>
>> 		talk-transit at openstreetmap.org; '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: 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
>>
>>
>>
>>
>>
>> 		_______________________________________________
>>
>>
>> 		Talk-transit mailing list
>>
>>
>> 		Talk-transit at openstreetmap.org
>>
>>
>> 		http://lists.openstreetmap.org/listinfo/talk-transit
>>
>>
>>
>>
>>
>>
>> 	_______________________________________________
>> 	Talk-transit mailing list
>> 	Talk-transit at openstreetmap.org
>> 	http://lists.openstreetmap.org/listinfo/talk-transit
>>
>>
>
>

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