On 2017-11-20 23:47, Warin wrote:
Hi,
There have been attempts in the past to add sub tags to
man_made=survey_point
https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dsurvey_point
To me there are 2 'types'. they are quite different;
Triangulation (or 'trig point') that are visible over quite some distance (say
over 2 km),
used to triangulate a position without having to go to the mark. Usually a pole
standing on top of a rise/hill.
Benchmarks that are visible on the surface but cannot be sighted at any
distance. They can be small brass plaques fastened to the ground or engraved
into stone.
These are used by surveyors by placing a tripod over the mark, thus have to be
locally approached.
If consideration is given to
https://wiki.openstreetmap.org/wiki/Seamarks/Categories_of_Objects#Control_Points_.28CATCTR.29
then expanding survey_point in a similar manner could be
survey_point:configuration=triangulation/benchmark
I use 'configuration' rather then 'type' or 'category' as it is more specific
as to what is meant.
Any thoughts?
Are there any other configurations?
It would be useful to tag the physical style of the survey point. ie the
size and shape and what it is made of. Is it a pillar, or just a metal
plate or bolt on the ground. This would tell you whether it is an
obvious landmark or not.
Tagging what the survey point is used for is a separate thing. ie
triangulation, or a benchmark. Nowadays most trig points are redundant,
so they are not actually used for any sort of survey work. Though in the
UK there are some still maintained as "passive stations", plus a few
"active stations" (with a GPS receiver).
Note there are some "Fundamental Benchmarks", which are a small stone
pillar.
Some of the common types in the UK: http://trigpointing.uk/wiki/Types
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