Comments
RedTreeDecember t1_j29wro8 wrote
So what do they go back and re-measure where they are at some interval?
namico2000 t1_j2a3bg5 wrote
Yes, the exact location of the marker was recorded when it was put in, the X, Y, and Z (elevation) coordinates. They use it as a control to measure from. You might see things like this, which are temporary measuring targets, periodically. They're really important for having a baseline to go from to figure out if things have shifted/moved over time.
LilGeographersRoom OP t1_j29co4d wrote
Is there a reason these are branded with Metro specifically?
the_real_dmac t1_j2a744q wrote
Much of the metro’s miles of tunnels were constructed using cut & cover, digging down from the surface, pouring concrete and laying steel, then covering it back up. (Not the deep stations along the redline, those were bored into bedrock). Disrupt that much soil and there will be compaction that occurs years later, and that can damage infrastructure built above. So metro monitors surface elevations around tunnels for that problem.
TorontoNeverSkeets t1_j2af87h wrote
Correct
LilGeographersRoom OP t1_j2du9gv wrote
Does Metro maintain these discs alone, or do they keep their measures in tangent with USGS?
TorontoNeverSkeets t1_j29p2l1 wrote
My guess is because they’re for doing monitoring on/around wmata property. Probably used for some combination for new construction and or vibration/settlement monitoring.
aegrotatio t1_j2a84v7 wrote
Even when very far away from Metro entrances on the surface you are still standing above or near a station, tunnel, or other Metro structure. Metro stations are massive.
_TW06_ t1_j29rjmr wrote
They are indeed survey markers… explore this map, it’s pretty interesting.
SimpleKnight89 t1_j29dn44 wrote
Illuminati clearly look at that
hipoetry t1_j29gz16 wrote
I don't know, but I found this article on old manhole covers in DC. Some are from the 1800s! Pretty cool.https://ggwash.org/view/62399/theres-history-to-behold-on-some-of-dcs-old-manhole-covers
Shonuff8 t1_j2bf2d0 wrote
Can confirm, have seen some of the sewer manholes stamped with 1880-90 dates around the Navy Yard area.
WhatsUpSteve t1_j2a80wr wrote
Survey markers.
V_T_H t1_j29e3is wrote
I don’t think it’s referring to “Metro” like “the Metro”, I think it’s referring to “Metro” like “Metropolitan Police Department” does. It’s referring to the city and their land survey group, not the public transportation.
ChubsBronco t1_j29osar wrote
It is referring to WMATA Metro.
AngelsGoHome t1_j29oluk wrote
I think they just might be "the Metro" survey pins. It seems the placing agency labels their pins (e.g., USGS) which helps identify the owner.
Metro obviously has critical infrastructure around and in between stations.
veloharris t1_j29rxf6 wrote
It is indeed referring to "Metro".
XComThrowawayAcct t1_j2a8zkm wrote
The survey marker serves as a verified control point. When on site, it’s the one point you know it’s location to within acceptable tolerances. Everything else on site — everything — is measured trigonometrically relative to that point.
(These are not used anymore because we have GPS now. It provides a virtual survey marker almost anywhere, any time. We are living in the future.)
beeporn t1_j2an6y3 wrote
A survey datum
DodgingTrains t1_j2by3zz wrote
The A06 on it indicates that this picture was taken near Van Ness.
Can the OP confirm?
LilGeographersRoom OP t1_j2dtz74 wrote
It was right in front of the Zoo entrance on Connecticut Avenue
[deleted] t1_j2dyrnb wrote
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keyjan t1_j29bxq4 wrote
You’ll see them for other buildings, utilities, etc. What Toronto said.
Successful-Plate3598 t1_j2a4r8n wrote
Usually these are used to show changing elevation over the years
SeattleCardboard t1_j2aojjj wrote
You'd have to expand on that. I would say the main use of a survey marker is for a surveyor/contractor/engineer to have as a control point. As mentioned by others it gives you an x,y,z based off of a known datum that you can use as a reference point.
The tree is 100' west of this survey marker and 10' higher. We know that the survey marker is at 10000,10000,100 then the tree would be at 9900,10000,110.
That's an easy example and what I would say is their most common use.
When you reference changing elevation that sounds like a high water mark, which is not what is shown in OPs picture.
[deleted] t1_j2bwr6g wrote
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TechByDayDjByNight t1_j2by1r2 wrote
Looks like survey level points.
There's registery that marks the elevation point if these so when someone does a survey they start at a marker and measures tge difference in elevation surrounding areas are compared to it
No-Tie5914 t1_j2d64ah wrote
We are the control group and the survey is on us 😂
WaterBubbly t1_j29nq82 wrote
Literally has information upon it to help you determine what it is
TorontoNeverSkeets t1_j29am3w wrote
They’re surveying monuments. Used for horizontal and vertical location. USGS has a database that would contain this monument’s lat/lon SPC etc.