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 <[email protected]
<mailto:[email protected]>> 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 <[email protected]
<mailto:[email protected]>> 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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