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<p>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.<br>
</p>
<div class="moz-cite-prefix">On 23/08/2020 12:27, SK53 wrote:<br>
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cite="mid:CAELijW_rgpF-cqZ2BE0TZeJ2Qc_umaGqcxB23z75+OMCKJhJTw@mail.gmail.com">
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<div>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 <a
href="https://www.openstreetmap.org/changeset/6041229#map=7/39.254/-6.124"
moz-do-not-send="true">Extremadura</a>). 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.<br>
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<div>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 (<a
href="https://www.ordnancesurvey.co.uk/business-government/tools-support/os-net/positioning"
moz-do-not-send="true">OS Net</a>). (From the OS website
"Ordnance Survey (OS) benchmarks and their heights haven't
been regularly maintained for over 40 years.").</div>
<div><br>
</div>
<div>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.</div>
<div><br>
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<div>Regards,</div>
<div><br>
</div>
<div>Jerry<br>
</div>
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<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, 23 Aug 2020 at 10:05,
Nick <<a href="mailto:nick@foresters.org"
moz-do-not-send="true">nick@foresters.org</a>> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I
have been looking at what is recorded under this tag in my
area. I see <br>
that there aren't that many and those that are on OSM refer to
trig <br>
points (see also <a href="http://trigpointing.uk/"
rel="noreferrer" target="_blank" moz-do-not-send="true">http://trigpointing.uk/</a>).
My thinking is that if these <br>
are accurate and precisely marked on OSM then perhaps they
could be used <br>
for resolving issue such as aerial imagery offsets.<br>
<br>
I therefore wondered if it was worth using other data under
this tag - <br>
specifically benchmarks (<a
href="https://www.ordnancesurvey.co.uk/benchmarks/"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://www.ordnancesurvey.co.uk/benchmarks/</a>)
<br>
as there are huge numbers in the UK. If these were marked on
OSM and <br>
their accuracy and precision verified (OS open data is to the
nearest <br>
10m square and transforming that adds errors), they could be
helpful in <br>
local surveys where they are less than accurate but also for
ensuring <br>
that moving all nodes in an area is valid (not just to match
aerial <br>
imagery). A possible linked organisation with data is <br>
<a href="https://www.bench-marks.org.uk/" rel="noreferrer"
target="_blank" moz-do-not-send="true">https://www.bench-marks.org.uk/</a><br>
<br>
Incidentally, the benchmarks can be helpful if you need to
align <br>
historical maps which have benchmarks shown.<br>
<br>
Any thoughts?<br>
<br>
<br>
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</blockquote>
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