#geodetic survey

[nnctales]

Exploring the Diverse Landscape of Surveys: Unveiling Different Types

Introduction Civil engineering, as a discipline, relies heavily on accurate and comprehensive data to design, plan, and construct various infrastructure projects. Surveys play a crucial role in gathering this essential information, providing engineers with the data needed to make informed decisions. There are several types of surveys in civil engineering, each serving a unique purpose. In this…

[carpe-mamilia]

Earlier this year my partner and I climbed Mount Sunday, the filming location for Edoras in The Lord of the Rings. At the very top of it was this:

[dataservices123]

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[agus0508]

Jual Gps Geodetic Hi Target GNSS RTK iRTK-5 Di Distributor Indonesia

[maipura]

#surveyor hat, precision meet the wild

[uss-edsall]

So there’s something called a ‘geodetic control point.’ These are used by surveyors to create accurate map measurements. There’s over a million in the United States, which the National Geodetic Survey uses to ensure the government’s maps are all accurate. It’s extremely important that these things are more accurate than any measurement you do on top of it, so they’re usually extremely stable markers. Most of the time it’s metal caps or rods buried in the ground

Washington D.C. has a couple of them, of course.

Next to the Washington Monument is a manhole cover in the grass.

That manhole does not lead to a sewer - it’s the top of a control point. But unlike most control points that are simple rods, this one is unique…

… for this control point is a mini replica of the Washington monument buried right next to the full size one.

[todays-xkcd]

In addition to 'squishy', after reviewing my submitted intraplate ground motion data, the National Geodetic Survey has politely asked me to stop using the word 'supple' so often when describing Midwestern states.

Minnesota [Explained]

Transcript

[Hairy standing in front of Ponytail and Cueball, who are sitting behind a desk] Hairy: Does anyone have any other concerns? Cueball: I'm concerned that Minnesota is getting shorter.

[A map of Minnesota beside Cueball, with arrows pointing from the northern and southern borders towards the middle] Cueball: Because of post-glacial crust rebound, the northern border is moving toward the southern border. It's less than an inch a decade, but I still don't like it. Cueball: Minnesota shouldn't be squishy.

[Hairy again standing in front of Ponytail and Cueball at the desk. Ponytail is looking at Cueball, whose finger is now raised in the air, gesturing] Hairy: Okay. Does anyone have any concerns related to the topic of this meeting? Cueball: All meetings should be about Minnesota until we resolve this.

[ltwilliammowett]

Reflecting circles

The reflecting circle was invented by the German geometer and astronomer Tobias Mayer in 1752, with details published in 1767. His development preceded the sextant and was motivated by the need to create a superior surveying instrument.

A Mayer circle, 18th century

It is a complete circular instrument graduated to 720° (to measure distances between heavenly bodies, there is no need to read an angle greater than 180°, since the minimum distance will always be less than 180°). Mayer presented a detailed description of this instrument to the Board of Longitude and John Bird used the information to construct one sixteen inches in diameter for evaluation by the Royal Navy. This instrument was one of those used by Admiral John Campbell during his evaluation of the lunar distance method. It differed in that it was graduated to 360° and was so heavy that it was fitted with a support that attached to a belt. It was not considered better than the Hadley octant and was less convenient to use. As a result, Campbell recommended the construction of the sextant.

Jean-Charles de Borda further developed the reflecting circle. He modified the position of the telescopic sight in such a way that the mirror could be used to receive an image from either side relative to the telescope. This eliminated the need to ascertain that the mirrors were precisely parallel when reading zero. This simplified the use of the instrument. Further refinements were performed with the help of Etienne Lenoir. The two of them refined the instrument to its definitive form in 1777. This instrument was so distinctive it was given the name Borda circle or repeating circle. Borda and Lenoir developed the instrument for geodetic surveying. Since it was not used for the celestial measures, it did not use double reflection and substituted two telescope sights. As such, it was not a reflecting instrument. It was notable as being the equal of the great theodolite created by the renowned instrument maker, Jesse Ramsden.

A Jean-Charles de Borda circle, by Étienne Lenoir 1775

Josef de Mendoza y Ríos redesigned Borda's reflecting circle in 1801. The goal was to use it together with his Lunar Tables published by the Royal Society. He made a design with two concentric circles and a vernier scale and recommended averaging three sequential readings to reduce the error. Borda's system was not based on a circle of 360° but 400 grads (Borda spent years calculating his tables with a circle divided in 400°). Mendoza's lunar tables have been used through almost the entire 19th century. Edward Troughton also modified the reflecting circle. He created a design with three index arms and verniers. This permitted three simultaneous readings to average out the error.

A Troughton Circle, 1803

As a navigation instrument, the reflecting circle was more popular with the French navy than with the British.

M. Daumas, Scientific Instruments of the Seventeenth and Eighteenth Centuries and Their Makers, London 1989

William Edward May, A History of Marine Navigation, G. T. Foulis & Co. Ltd., Oxfordshire, 1973

Richard, Dunn, Navigational Instruments, London 2016

[nightpool]

In addition to 'squishy', after reviewing my submitted intraplate ground motion data, the National Geodetic Survey has politely asked me to stop using the word 'supple' so often when describing Midwestern states.

[ronsenthal]

I can't fucking believe my nerdy cartography ass never noticed that they showed a Survey Marker on the top of Currahee

So I did a quick search on the National Geodetic Survey online map and I found there are three SM on the site but the descriptions on the database doesn't match as they don't even mention the structure as we see on the pic above, so my nerdy ass is confused as fuck now

[script-a-world]

Submitted via Google Form:

How easy is it for a GPS system to include elevation? Because my world has so many layers and levels, any GPS system would need heights included.

Tex: GPS relies on a network of satellites talking to each other while they bounce information off the surface of the planet (Wikipedia). To work purely off a surface and not any underlying surfaces, you could theoretically include “height” as a function of how long it takes a radio wave to come back to the satellite given a standardized orientation point of zero-height (i.e. sea level) as an additional variable in the data it calculates. A lot of this is already calculated in an end-user’s GPS receiver as four-dimensional space via the input of multiple satellites (Wikipedia 1, Wikipedia 2). Elevation and sub-surface levels are different kettles of fish, however, and the latter would have difficulty being perceived by satellites due to the interference of what I’m presuming are layers of buildings above it. You could possibly install relays on each level that map each interior section, and have that data continuously sent to the satellites, but it might be patchy and prone to dark spots in coverage.

Addy: Hello! I actually have some experience with this. So for GPS as it works now, you get a set of x-y coordinates, and then those coordinates are applied to a geodetic model (model of Earth's shape) to get the elevation for that height. For surveying purposes, you'll often adjust from that for whatever datum (coordinate reference, different ones are used for different regions or purposes) you're using. For elevation, that can be +/- 5-30 feet (or more, that's just what I remember from class examples) (x & y also tend to have smaller adjustments). It also assumes only one elevation per location.

That's part of why modern GPS systems tend to struggle with overpasses or overlapping roads - they can't tell which one you're on. Also, when you have large masses above you, that tends to block a lot of the signal.

If GPS is being used for navigation, could a user simply input what level they're on? (assuming a Coruscant-style system, where the levels are distinct) From there, the program could simply draw the route as normal, since the starting and ending elevations are now both known.

Wootzel: Maybe a way to let your GPS be accurate through all the levels is to augment it with some other system. Maybe when any GPS passes between levels, there’s some kind of signal point that it reads to know what level it’s entering?

As Tex mentioned though, GPS as we know it absolutely sucks when there’s much interference between it and the satellites it relies on. GPS is currently the world’s most universal navigational aid because it doesn’t require being near any kind of communication device on the surface, but the minute you go into a tunnel or even into a large building, it loses signal and the accuracy plummets, or it just fails altogether. 

To make it plausible that your navigation systems work through the levels of infrastructure on your world, you might want to augment it with some other system, maybe toss in some kind of nod to the signals being something that is interference-resistant (what that could reasonably be, I do not know), or augment a satellite system with something built into the structures that the devices can also use to coordinate their position. 

[dataservices123]

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