2920: Survey Marker

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Survey Marker

Title text: Fun fact: The standard North American NAD83 coordinate system is misaligned from the actual Earth, off-center by about 7 feet. Someone knows where I am, and I'm in the wrong place.

Explanation

Cueball and Megan have found a survey marker on the ground. Survey markers such as these are used as reference points for the NAD 83 and NAVD 88 geodetic reference systems, and the U.S. National Geodetic Survey has a database storing the coordinates of these markers. However, those two systems are being replaced by the New Datums of 2022 (delayed to 2024-2025), which is primarily based on satellite systems and gravimetric models.

When they update the database in the comic, Cueball's position, both horizontal and vertical, changes to compensate, leaving him panicking in mid-air. In reality, updating a database to change the coordinates of a location would not physically move items at the location.^{[citation needed]} Arguably, if they did, no one would notice much, since everything surrounding them should similarly move simultaneously to its corrected position as well. On the other hand, if the markers were updated and moved relative to each other, and (as the comic suggests) items shifted based to match the new markers, this could mean that objects would be stretched or compressed depending on whether the new markers were closer or further away from each other from their previous positions. However, in the comic, the only things whose position is 'known' (and can therefore be 'corrected') are those that are directly on a marker, hence why this shifting does not seem to apply to Megan (or her phone).

The title text refers to NAD 83 being around 7 feet off. This probably refers to the difference of about 7.2 feet (2.2 m) in the positioning of the centers of the notional Earth ellipsoids used as the basis for NAD 83 and WGS 84. This is also one of Randall's fun facts.

Absurd outcomes from differing survey standards was also the topic of 2888: US Survey Foot.

Transcript

[Zoomed in view of a round marker on the ground, with small specks of dirt around it. There is one line of text going around the central part in the outer rim of the marker, with the first three words written around the top, and the last two words written around the bottom (thus not text that are going all the way around in one single line). Inside this rim there are more text on three lines. In the center there is a small cross in a triangle pointing up in relation to the central text. There are more unreadable text below the last line of text and around the inner part of the rim. And off panel voice, which in the next panel turns out to be Cueball, is written above the mark.]

U.S. Geological Survey bench mark

Elevation above sea 447 feet

Cueball (off-panel): I love finding these survey markers. It's somehow reassuring.

[Cueball and Megan are shown as they look down on the marker. Cueball has one leg on either side of the marker and Megan stands to the right.]

Cueball: I like that someone, somewhere, knows where this spot is.

Cueball: If I stand on it, they know where I am.

[Cueball and Megan look up at each other.]

Megan: But the NAD83 and NAVD88 datums are getting replaced soon. That marker's coordinates could shift by like 5 feet.

[Megan is looking down at her phone in her hand, standing in the same place in relation to the marker. Cueball is now floating in the air behind her about 5 feet above the ground, while flailing with his arms and legs (as shown with three small curved lines at the end of either arm and above and below him).]

Megan: Oh look, it just got updated.

Cueball: Hey! Put me back!

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Discussion

"datums." JohnHawkinson (talk) 14:38, 16 April 2024 (UTC)

FWIW, there is a marker at the end of my street, and I have seen others. I know "in the ground" is a figure of speech; all I have seen near here were set in rock (often with molten Lead/Zinc) so they didn't travel. My road we have boulders nobody is likely to move. Other places like Appalachian Trail, set in the mountain stone. In sandy South Jersey they dump a couple tons of concrete and set the marker in that. --PRR (talk) 23:41, 16 April 2024 (UTC)

I like to think our myriad calendars & leap days & time zones & daylight savings time & mapping coordinate offsets, are all orchestrated specifically to complicate time travel. Have fun materializing halfway into the ground, or entirely out of the ecliptic, time travel wankers. ProphetZarquon (talk) 06:30, 17 April 2024 (UTC)

A fairly old 'time travel failure' trope is a time machine that only travels in time. If you go back (or forward) six months, you find yourself in space in exactly opposite the Earth (which is now half way round its orbit).

Yes, there's also solar-galactic motion and galactic-extragalactic, and tends to date back to an era where a universal/local æther was predominant as 'the one true frame of reference'. But even a more arbitrary-frame 'locking' isn't movement-free. H.G. Wells's traveler in time apparently sat still in his location, but seems to ignore/handwave all kinds of issues of long-term soil accumulation/weathering, tectonics, etc. Or the very basic (but vital) acknowledgement that only in freefall can you not be in a continually revised 'frame', as merely standing still under gravity you're accelerating.

However much detail there is, in the source material, there's pretty much always a fudge in a object-type time-machine (as opposed to a portal-style, which will have its own 'rules') that also gives it a "necessary secondary supwerpower" of space-movement, even if only to stay (apparently) in the same place and not then try to merge its atoms with whatever solid things (gases, even liquids, generally being already handwaved as inconsequential!) might happen to be in the 'landing zone'.

It's gross failures (or 'exact word' strictness) in the space-travelling element that can cause plot-driving surprises to the protagonist(s) involved. (Perhaps I'm here at least in part harking back to the 'retro-canon-crossover' work that was The Space Machine.) 172.69.43.164 09:47, 17 April 2024 (UTC)

Oh, I'm quite familiar with that concept! That's what put the idea in my head. If the frame of reference isn't fixed, you'd need fairly precise coordinates to arrive at, but even with a Wells type time-machine that somehow stays in "place", any plans to travel to the time of a specific event, could be severely impacted by an offset of hours or days or sometimes weeks (I blame Salem Saberhagen for the 13 day festival of Bobunk getting lost in the switch to the Gregorian calendar). I like to imagine our messed up time & calendar system is a defense intentionally maintained by a Section 31 type organization, to make it harder for "enemy" time-travelers to know exactly when (& potentially where) pivotal historic events occurred. The rest of the multiverse could be running on a Mayan calendar & using sidereal clocks or Unix time et cetera, while our one reality has us split into zones that may or may not use "daylight savings", & anything farther back than a skipped leap day, would require an extra wait or time jump for a Wells type machine & would likely result in a total miss for machines that need exact coordinates. On its own, security through obfuscation is a lousy defense, but if we presume the existence of a "temporal security" force, even a 1hr time difference could grant some opportunity to interdict the errant traveler. Switching it up in a few places every so often, could really frustrate travelers.

"Help defend our timeline, make the switch to Swatch time 'today'!"

ProphetZarquon (talk) 13:50, 17 April 2024 (UTC)

Unless that specific marker was under 24/7 monitoring, nobody would actually know when/if Cueball was standing on it. These Are Not The Comments You Are Looking For (talk) 06:15, 21 April 2024 (UTC)

This reminds me of the prime meridian that's laid out on the ground at the Greenwich Royal Observatory for tourists to stand on. Unfortunately, it uses an old datum and the actual prime meridian under WGS84 is about 100 metres to the East. Fortunately, the British Isles are moving slowly North East so the two meridians will coincide at some point. Jeremyp (talk) 09:09, 17 April 2024 (UTC)

I use to live in a flat about a mile south of the Greenwich observatory and there was a marker for the meridian in the pavement (sidewalk) outside the flat.--172.70.85.13 07:54, 18 April 2024 (UTC)

The other day I had reason to pass by a 'countryside' Prime Meridian sign (and plaque-on-a-brick-plinth, IIRC), at a seemingly arbitrary point very near where it eventually crosses the coast into the North Sea (if they don't have a sign on the coast, I'd be surprised, but I had no cause to go across that way too).

Having manually adjusted that URL to be explicitly zero east/west, it may well be that map-zero doesn't match the 'signed' zero. The physical location would likely be (without checking StreetView for accurate confirmation) that little stub of apparently inconsequential footpath, north off Welwick Road, just a little to the east of the "P"arking spot (a rough layby, clearly intended purely for the odd passerby who wishes to park up and peruse the signage). Which might well be 100m W (minus adjustment for approximately 2° latitude's additional longitudinal curvature) of the web-page centre when forced to display a nominative 0° position. 172.70.163.49 12:12, 18 April 2024 (UTC)

Interesting. Back in the sixties we had family holidays in Cleethorpes, the other side of the Humber, and I remember a mark on the coastal footpath indicating the meridian.--172.70.90.114 07:54, 19 April 2024 (UTC)

Wow, something I've never seen or heard about, talked about like it's common knowledge and everyone has experienced them. That's VERY unusual for me these days... This thing is news to me... NiceGuy1 (talk) 05:14, 20 April 2024 (UTC)

I recall seeing these. They usually took the form of a 6"x6"x6" concrete / stone cube with the marker imbedded on top. These Are Not The Comments You Are Looking For (talk) 06:11, 21 April 2024 (UTC)