[Talk-GB] Possible use of OS triangulation stations to determine aerial imagery offset

Greg gregrs at fastmail.co.uk
Sun Sep 4 20:31:37 UTC 2016

Hi Dave F,

I haven’t thought too much about the process at this stage, but I was imagining it would be done mostly programatically as there are 21,000+ (non-destroyed) stations.

However, I was anticipating that there would have to be at least some manual intervention to decide whether OS trig stations near OSM ‘survey_point’s are the same thing and merge the tags. I’m sure some sort of filtering of near-certain, possible and unlikely matches between OS trig stations and OSM survey_points will help, but I’m not convinced that setting a hard limit (e.g. OSM ‘survey_point’s within 5m of an OS trig station must represent that station) will work entirely.

If someone created a single CSV of all the triangulation stations *including flush bracket numbers*, perhaps using the data from [https://www.ordnancesurvey.co.uk/gps/legacy-control-information/triangulation-stations] (which I asked OS about [http://wiki.openstreetmap.org/wiki/User:Gregrs/Ordnance_Survey_triangulation_stations/Licence_emails]) the flush bracket numbers could also be checked against any existing OSM ‘ref’s.

OS customer services helpfully pointed me in the direction of https://groups.yahoo.com/neo/groups/trigonomy/info as another source of flush bracket numbers, but I haven’t asked them about licensing, nor have I contacted anyone from the Trigpointing website at this stage.


> On 2 Sep 2016, at 00:05, Dave F <davefoxfac63 at btinternet.com> wrote:
> Could you clarify if by merge/import you mean it to be performed manually or programmatically?
> Personally I think manually is the way to go, possibly as a Quarterly Project asimilar to the schools update. Local knowledge will definitely produce more accurate results.
> I'd use P2's Task to save all that panning around.
> Have you been in contact with anyone from the Trigpointing website?
> Cheers
> Dave F.
> On 01/09/2016 17:16, Greg wrote:
>> Hi all,
>> Since my last email, I've analysed the relationship between the OS
>> triangulation station data and OSM 'man_made=survey_point's in Great
>> Britain. You can read about this on my wiki page
>> [http://wiki.openstreetmap.org/wiki/User:Gregrs/Ordnance_Survey_triangulation_stations].
>> I believe it may be possible to import/merge this data at some point in
>> the future so I'd be grateful if you could take a look.
>> I have also converted the data into a GPX file with metadata that can be
>> understood/displayed by JOSM to allow users to more accurately determine
>> the offset of aerial imagery. This can be obtained here:
>> [http://gregrs.dev.openstreetmap.org].
>> Thanks,
>> Greg.
>> On Fri, Aug 19, 2016, at 08:08 PM, Greg wrote:
>>> I'm pleased to say that I have had confirmation from Ordnance Survey
>>> that their triangulation station data can be used under the Open
>>> Government Licence v3. I have documented this on the wiki:
>>> [http://wiki.openstreetmap.org/wiki/User:Gregrs/Ordnance_Survey_triangulation_stations].
>>> I will try to look into making this data more accessible to the
>>> community so that it can be used to more accurately determine the offset
>>> of aerial imagery. I have experimented with this idea around the Rugby
>>> area and it seems to work well.
>>> I am also in the process of analysing the relationship between this data
>>> and the large number of 'man_made=survey_point's already in the database
>>> in order to determine whether it might be feasible/useful to
>>> import/merge the data. It looks like similar data has been imported from
>>> IGN in France. Of course I won't do this until it's been properly
>>> discussed.
>>> Thanks,
>>> Greg.
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