[Talk-GB] man_made=survey_point

[Nick]

Thanks Jass - I was not aware of this excellent piece of work by Greg - 
do we know if the proposals "Possible import" were followed through?

I wonder if OS have other data for the 'benchmarks i.e. more precise 
than the data currently available.

On 23/08/2020 15:26, Jass Kurn wrote:
> Gregrs has provided converted data for trig points, with the data 
> obtained from a FOI request. They created a page to explain the 
> process, and made available the converted data as a gpx file 
> https://wiki.openstreetmap.org/wiki/Ordnance_Survey_triangulation_stations .
>
> Jass
>
> On Sun, 23 Aug 2020 at 15:13, Nick <nick at foresters.org 
> <mailto:nick at foresters.org>> wrote:
>
>     My thinking was that most people surveying would not use accurate
>     and precise systems such as differential GPS and/or RTK. So if
>     these systems were used to accurately and precisely locate
>     distinct local markers (i.e. trig points, benchmarks etc.) then
>     local surveys could potentially use these to refine/check their
>     own surveys. This approach would still be based on community input
>     but could be used as an approach to education (e.g. local schools
>     involved) as to how surveying works in practice.
>
>     On 23/08/2020 12:27, SK53 wrote:
>>     This approach has been advocated in other European countries, and
>>     the Spanish community imported all the points of the national
>>     geodesic network (e.g., for Extremadura
>>     <https://www.openstreetmap.org/changeset/6041229#map=7/39.254/-6.124>).
>>     They more or less violate the idea of OSM as something which is
>>     community contributed (IIRC each point has "DO NOT MOVE") and
>>     often interfere with objects which do need mapping (churches are
>>     a particular point). It's not clear that this import has assisted
>>     improved accuracy of mapping in Spain.
>>
>>     Many trig pillars are now way out of alignment and mainly of
>>     interest as an artefact. Even benchmarks might not have much
>>     relevance as OS surveying mainly uses differential GPS with
>>     reference to their own base network (OS Net
>>     <https://www.ordnancesurvey.co.uk/business-government/tools-support/os-net/positioning>).
>>     (From the OS website "Ordnance Survey (OS) benchmarks and their
>>     heights haven't been regularly maintained for over 40 years.").
>>
>>     OS Net is effectively proprietary, there are a limited number of
>>     open base stations for differential GPS in the UK. I do believe
>>     differential GPS (RTK) has a role to play in OSM surveying,
>>     although for specific purposes rather than generic improvement of
>>     feature alignment.
>>
>>     Regards,
>>
>>     Jerry
>>
>>     On Sun, 23 Aug 2020 at 10:05, Nick <nick at foresters.org
>>     <mailto:nick at foresters.org>> wrote:
>>
>>         I have been looking at what is recorded under this tag in my
>>         area. I see
>>         that there aren't that many and those that are on OSM refer
>>         to trig
>>         points (see also http://trigpointing.uk/). My thinking is
>>         that if these
>>         are accurate and precisely marked on OSM then perhaps they
>>         could be used
>>         for resolving issue such as aerial imagery offsets.
>>
>>         I therefore wondered if it was worth using other data under
>>         this tag -
>>         specifically benchmarks
>>         (https://www.ordnancesurvey.co.uk/benchmarks/)
>>         as there are huge numbers in the UK. If these were marked on
>>         OSM and
>>         their accuracy and precision verified (OS open data is to the
>>         nearest
>>         10m square and transforming that adds errors), they could be
>>         helpful in
>>         local surveys where they are less than accurate but also for
>>         ensuring
>>         that moving all nodes in an area is valid (not just to match
>>         aerial
>>         imagery). A possible linked organisation with data is
>>         https://www.bench-marks.org.uk/
>>
>>         Incidentally, the benchmarks can be helpful if you need to align
>>         historical maps which have benchmarks shown.
>>
>>         Any thoughts?
>>
>>
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