On 18/04/13 16:40, Oliver Jowett wrote:
On Thu, Apr 18, 2013 at 3:02 PM, Chris Hill <o...@raggedred.net
<mailto:o...@raggedred.net>> wrote:
On 18/04/13 14:14, Shaun McDonald wrote:
On 18 Apr 2013, at 13:01, "Dave F." <dave...@madasafish.com
<mailto:dave...@madasafish.com>> wrote:
On 18/04/2013 12:52, Shaun McDonald wrote:
Updates are a lot harder to do as you have to deal
with differences
When you say differences, do you mean within the tags?
Does it need to do that, could it not do a simpler find &
replace?
If someone has modified the item in OSM and in NaPTAN then it
needs manual intervention as to which is more correct - the
one in OSM or the one in NaPTAN.
Shaun
There are various errors in NaPTAN data. The data was created by
different means in different local authorities and to varying
standards of quality. The position is not always very accurate,
but sometimes the accompanying information can be poor too. Some
data are very good, but until you survey it you just don't know.
As someone who has manually validated every stop in in a city
(~1300) and about a third (~900) of the stops in a large Unitary
Authority I can vouch for the differences and the wide variation
in quality. It became clear that in the city the quality varied
from area to area. I suspect that some areas were surveyed or
recorded or checked more diligently than others possibly because a
more diligent or competent person did the work there.
Can I ask what type of changes you made to the NaPTAN data when
manually validating the stops?
I've been meaning to look at exactly this - updating the NaPTAN
imported data - for a little while now as it's needed before the TNDS
data (which has route / timetable info) can be usefully used.
My rough plan was to assume that all tags under the naptan: namespace
were fair game for updating to match the current NaPTAN import.
Whether that's practical will depend on if there have been widespread
manual changes to the naptan: data or not.
I followed the guidelines in the wiki [1] and use the NOVAM viewer [2]
to see what remained to be reviewed. Positioning is the biggest dilemma,
how to be sure the position should be moved? Multiple GPS traces to
average out the road position helps a lot, but a single GPS position is
subject to the same error as some of the original surveys. Any naptan:*
tag is fair game to change if it does not agree with your survey.
[1]
http://wiki.openstreetmap.org/wiki/NaPTAN/Surveying_and_Merging_NaPTAN_and_OSM_data
[2]
http://mappa-mercia.org/novam/?zoom=15&lat=53.7299&lon=-0.43507&layers=BT&scheme=hull
--
Cheers, Chris
user: chillly
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