On 21-Nov-17 12:07 PM, Andrew Harvey wrote:
Being able to distinguish different types of survey marks and points
is very much needed in OSM, it would be great to see this formalised
on the wiki.
I like the idea of modelling it after
https://wiki.openstreetmap.org/wiki/Seamarks/Categories_of_Objects#Control_Points_.28CATCTR.29
<https://wiki.openstreetmap.org/wiki/Seamarks/Categories_of_Objects#Control_Points_.28CATCTR.29>
as that seems well thought out.
I like the idea of using configuration as a sub key to survey_point,
rather than the undocumented by suggested tags of
"triangulation_point=yes and benchmark=yes".
My only question is the wiki page currently says "Since multiple
survey points are possible on one object (eg. a benchmark on a
triangulation point/pillar) then in order to avoid multiple values
within one key, such as a semicolon-delimited list in survey_point=*,
it may be advisable to use something like triangulation_point=yes and
benchmark=yes to allow clean coexistence of tags on one node.".
I think that triangulation points are not normally used this way? Where
required the placement of the equipment on the exact centre of the point
may mean that the structure needs to be disassembled.
I'd think any triangulation point could be used this way as a bench mark
and they may all be equipped for it?
Might have this from one of Len Beadells' books? Or from talks with a
past neighbour - a professional surveyor.
How would your proposal work with multiple survey points on the one
object? I've never come across this so not sure myself.
Any professional knowledge on this would be welcome.
I think observation is a valid configuration, as I've seen
observatories used as the datum on old maps.
Any place can be used as an 'observation point' .. so I don't see any
reason to map something that has no ground presence?
Or is there some artefact left behind? And then would not that be a form
of benchmark?
On 21 November 2017 at 10:47, Warin <61sundow...@gmail.com
<mailto:61sundow...@gmail.com>> 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
<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
<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?
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