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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