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<p>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?</p>
<p>I wonder if OS have other data for the 'benchmarks i.e. more
precise than the data currently available.<br>
</p>
<div class="moz-cite-prefix">On 23/08/2020 15:26, Jass Kurn wrote:<br>
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<div dir="ltr">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 <a
href="https://wiki.openstreetmap.org/wiki/Ordnance_Survey_triangulation_stations"
moz-do-not-send="true">https://wiki.openstreetmap.org/wiki/Ordnance_Survey_triangulation_stations</a> .<br>
<br>
Jass<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, 23 Aug 2020 at 15:13,
Nick <<a href="mailto:nick@foresters.org"
moz-do-not-send="true">nick@foresters.org</a>> wrote:<br>
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0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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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>On 23/08/2020 12:27, SK53 wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<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"
target="_blank" 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>
</div>
<div><br>
</div>
<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"
target="_blank" 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>
</div>
<div>Regards,</div>
<div><br>
</div>
<div>Jerry<br>
</div>
</div>
<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"
target="_blank" moz-do-not-send="true">nick@foresters.org</a>>
wrote:<br>
</div>
<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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