[Talk-GB] man_made=survey_point

[Nick]

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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