[Tagging] Feature Proposal - RFC - Survey Markers

[Kevin Kenny]

I suspect that the lifecycle prefix is more useful than you might imagine.
"No visible traces" depends on the observer in a great many cases.
Certainly if the mark was on a demolished building or a destroyed bridge
abutment, it's gone, and I'd concede it's no longer of value to OSM.
Nevertheless, I know that I've recovered 'destroyed' trig points
(originally marked with bronze tablets like
https://flickr.com/photos/ke9tv/29348215163) and located the drill holes in
the rock (confirmed by observing that the hole was contaminated with the
sulphur that was used at the time to cement the marker).  Sometimes the
process of locating the marker was aided by finding a nearby witness post (/
https://flickr.com/photos/ke9tv/29681317420) or azimuth mark (
https://flickr.com/photos/ke9tv/8716584502).  If the hole can be found,
usually the mark can be placed to third-order or better accuracy.

There are some interesting corner cases like
https://flickr.com/photos/andyarthur/7404713306 - the USGS benchmark at
right has been vandalized. It had been placed at the tabulated location of
the still-extant Adirondack Survey marker at left.  You can certainly
recover the mark from the center of the tablet's stem, still embedded in
the rock.  The stamping on the earlier benchmark identifies it
unambiguously. Moreover, its placement was unbelievably accurate for the
time. The control network from that survey is still used to assess
continental drift and post-glacial rebound, since its marks are all
embedded in the stable rock of the Adirondacks, the southermost extension
of the Canadian Shield. That particular marker is moving in a generally WSW
direction at about 2.3 cm/year.

I'm also not quite sure I'd use 'destroyed' to describe one marker that I
strongly suspect is still virtually undisturbed, but buried under debris
from an avalanche.  But I'm not about to go digging to find out.

The databases seldom log a benchmark as 'destroyed' unless either (a) it
was on a structure known to be demolished or (b) its remains were
recovered. Instead, it's logged as 'not recovered' indicating that the
surveyor was unable to locate it after a diligent search. It's not too
uncommon for a 'not recovered' benchmark to be located at a later time.

You're right that serious surveyors will go for the databases.  But a lot
of people are hobby 'benchmark hunters' who may well use OSM, particularly
since most benchmarks in the US never made it into the databases because
there was never the funding to transcribe the paper files. (And the
authorities accept reports from benchmark hunters and geocachers and use
them to update the status of the marks!)


On Sat, Jun 5, 2021 at 7:52 AM Paul Allen <pla16021 at gmail.com> wrote:

> On Sat, 5 Jun 2021 at 07:27, Kyle Hensel via Tagging <
> tagging at openstreetmap.org> wrote:
>
> Some of the suggestions:
>>
>>
>>
>> 1. survey_point:condition=destroyed
>>
>> 2. former:man_made=survey_point (or a similar lifecycle prefix)
>>
>>
>>
>> I think the first option is better since a 'destroyed' survey marker is
>> still a valid survey point - Michael has explained this well in an earlier
>> message:
>> https://lists.openstreetmap.org/pipermail/tagging/2021-June/061700.html
>>
>
> I'm not sure that survey points for which there are no visible traces are
> mappable in OSM as such.  OSM is a map of visible objects (that's a
> simplification, but close enough for this).  I can understand
> why these positions are important to surveyors, but I don't think they meet
> OSM criteria for mappability (I could be very wrong about that).
>
> I can justify mapping some (not necessarily all) destroyed survey points
> with a lifecycle prefix to prevent them being resurrected by armchair
> mappers.
> I can't justify mapping destroyed/invisible survey points just because they
> were (and perhaps still are) used in surveys.  Surveyors have official
> databases of these and don't need OSM to locate them.  If there really is
> a need to integrate such a database with OSM there are tools like
> uMap and Leaflet that would allow that to be done.
>
> BTW, there are records of Ordnance Survey cut marks in buildings
> where it is noted that the building itself has been destroyed.  No
> matter how important that point was to past surveys, it is no longer
> there and I don't see how it could be considered usable.  Historical
> interest, perhaps, but we don't map history.
>
> --
> Paul
>
>
> _______________________________________________
> Tagging mailing list
> Tagging at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/tagging
>


-- 
73 de ke9tv/2, Kevin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tagging/attachments/20210605/89de59af/attachment-0001.htm>