[Talk-GB] man_made=survey_point

[Jass Kurn]

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> 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> 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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