From what I can tell that's a FM antenna
Yep. KDVS, the UC Davis campus radio station got that antenna 10 years ago. It's on a tower at the county landfill.
which uses fixed points such as true north, south, east, and west as references
OH the horrors. CHAT GPT still has not read enough to understand the vagaries of using the term "True North"
Yep. Here's what ChatGPT says about that:
The term "true north" typically refers to geographic north rather than astronomical north.
Geographic north, also known as true north, is the direction along the Earth's surface that points to the geographic North Pole. It is determined by the Earth's rotation axis and is independent of celestial observations. True north is commonly used as a reference for navigation and mapping purposes, and it is often represented by the vertical lines on maps or represented by the azimuthal angle of 0 degrees.
On the other hand, astronomical north, also called celestial north or astronomical true north, refers to the direction of the celestial north pole. It is determined by the Earth's rotation axis extended into space and intersects with the celestial sphere. Astronomical north is used in astronomy and celestial navigation for locating celestial objects and determining their positions.
While true north and astronomical north are related, they are not precisely the same. The difference between the two is due to the phenomenon known as polar motion, which causes the Earth's rotation axis to shift slightly over time. This means that the geographic North Pole and the celestial north pole are not in the exact same position, leading to a small angular difference between true north and astronomical north. However, for most practical purposes, this difference is negligible and true north is often considered synonymous with geographic north.
@mathteacher So, I see a new term for North. Geographic North. According to CHAT GPT why do we need a distinction between Geodetic North and Geographic North? Does CHAT GPT feel we should get rid of the term True North and instead describe correctly the north we are referring to i.e. Geodetic, Magnetic, or Astronomic? And perhaps due to my ignorance, it appears we may have a need to use a 4th distinction for north, Geographic.
If you can't tell already, True North is the pea under my mattress.
Off topic, but I had this exchange with ChatGPT earlier this mornning. It's perception is amazing.
Thank you for your kind words! As an AI language model, I am not related to Hal, the fictional computer from Arthur C. Clarke's "2001: A Space Odyssey." While both Hal and I are AI entities, we are separate and distinct creations. I am an instance of the GPT-3.5 language model developed by OpenAI, designed to assist with generating human-like text based on the input I receive. If you have any more questions or need further assistance, feel free to ask.
I knew about that pea under your mattress already. I used the term "geographic north" in the question, so I asked ChatGPT about geographic north and geodetic north:
No, "geographic north" and "geodetic north" are not equivalent terms. While they are related concepts, they have different meanings in the field of geodesy and geodetic surveying.
Geographic north refers to the direction of the North Pole along the Earth's surface. It is the direction towards which the lines of longitude converge as they approach the North Pole. Geographic north is commonly used as a reference for navigation and mapping purposes.
On the other hand, geodetic north refers to the direction of the local vertical at a particular location on the Earth's surface. It is determined by the plumb line or gravity vector, which points towards the center of the Earth. Geodetic north takes into account the shape of the Earth's surface, which is approximated as an ellipsoid, and considers variations in gravity across the Earth.
The difference between geographic north and geodetic north arises due to the irregular shape of the Earth and the effects of gravity. The Earth is not a perfect sphere but is better approximated as an ellipsoid, so the direction of the local vertical can deviate slightly from the lines of latitude.
In practical terms, the difference between geographic north and geodetic north is generally small and may be negligible for most applications. However, in precise geodetic surveys and calculations, it is necessary to consider the distinction between the two and account for the geodetic reference frame and the shape of the Earth.
So, while geographic north and geodetic north are related concepts, they refer to different aspects of the Earth's surface and have distinct meanings within geodesy and geodetic surveying.
@mathteacher OK. It appears I'm screwed if someone asks me to put their data on Geographic North. How does one make the correction from Geodetic to Geographic?
Anyone? Bueller? Bueller?
On second thought, Geographic must be the result of a Solar?
ChatGPT said:
astronomical north, also called celestial north or astronomical true north, refers to the direction of the celestial north pole. It is determined by the Earth's rotation axis extended into space and intersects with the celestial sphere
I disagree.
Astro north is what you observe from celestial bodies and bring down to the horizon without correcting for the deflection of the vertical at your location.
Then after applying the LaPlace correction you get a good estimate of geodetic/geographic north.
The ChatGPT definition doesn't make sense because it is nearly identical to geodetic.
Well, my question really required a follow-up:
True north is generally considered synonymous with geographic north. In most practical applications, the term "true north" refers to the direction towards the geographic North Pole along the Earth's surface.
True north is determined by the Earth's rotation axis and is independent of the irregularities in the Earth's shape and gravity. It provides a reference for navigation, mapping, and general orientation.
While there is a small angular difference between the true north (geographic north) and the geodetic north due to the irregular shape of the Earth and the effects of gravity, for most purposes, this distinction is negligible. True north is widely used as a practical and convenient reference direction, and it is typically considered to align with the lines of longitude on maps and in navigation.
In summary, when people use the term "true north," they are generally referring to geographic north, which is the direction towards the North Pole along the Earth's surface.
I don't know what to say, other than my brushes with the celestial sphere in Spherical Trig are consistent with ChatGPT. How that plays with observations, I don't know. If I stand at the end of my driveway and look over my across-the-street neighbor's roof, I can see Polaris, but that's the extent of my celestial observing.
ChatGPT is always ready to discuss such things, but it is stubborn, so you sometimes have to bore in on the topic with successive questions.
In any event, it's an exceptional learning tool that's likely to shake many long-held beliefs in many different fields.
This may help:
To reconcile geodetic north and astronomical north at a specific location, you can use a process known as astronomical azimuth determination. This involves making observations of celestial objects to determine the angular difference between the geodetic north (local vertical) and astronomical north (celestial north pole). Here's a general overview of the steps involved:
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Set up Observations: Choose a suitable location and time for the observations. Ensure that the sky is clear and free from obstructions that could obstruct the view of celestial objects.
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Select Reference Stars: Identify and select reference stars near the celestial north pole. These stars should be well-documented and have accurate celestial coordinates available.
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Determine Azimuths: Using specialized astronomical equipment such as a theodolite or a total station, measure the azimuths (horizontal angles) from the reference stars to the geodetic north (local vertical). This is typically done by aligning the instrument to the reference stars and measuring their angles relative to a reference direction, such as a plumb line.
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Calculate Difference: Compare the measured azimuths to the expected azimuths based on the known celestial coordinates of the reference stars. Calculate the angular difference between the measured azimuths and the astronomical north.
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Apply Correction: Apply the calculated angular difference as a correction to reconcile the geodetic north (local vertical) with the astronomical north. This correction can be considered as an adjustment to align the local vertical with the direction of the celestial north pole.
It's important to note that the process described above requires specialized astronomical equipment and expertise in celestial observations. It is typically carried out in precise geodetic surveys or in cases where accurate alignment between geodetic north and astronomical north is necessary, such as in astronomical observatories or celestial navigation applications.
For general navigation and mapping purposes, the difference between geodetic north and astronomical north is often negligible and can be disregarded.
Useless drivel. It still doesn't mention deflection of the vertical or Laplace correction, which any surveying textbook would discuss in this regard.
ChatGPT is dangerous because it appears so slick and authoritative but often gets things wrong.
There are stories out there of a lawyer who used it to find cases to cite. He was quite embarrassed and probably censured because some of the cases ChatGPT listed did not actually exist.
I've told my story of asking it about author Robert Heinlein. It said he was married three times, which I cannot find anywhere else, and it gave his third marriage year as later than his death year.
People complain about Wikipedia not being a good source, but it is head and shoulders over ChatGPT. Most wrong info on Wikipedia gets corrected by someone who knows.
Now, Bill, it's easy to scoff at something inhuman but perhaps not wise to dismiss it. After all, not many people are still lugging around Gunter's chains. And aren't there also stories of people driving into the ocean while following GPS? People misuse all sorts of tools.
Consider this phrase from the ChatGPT reply: "...to the geodetic north (local vertical)." Isn't it true that the local vertical is the plumb line, a vertical unadjusted for deflection of the vertical? And isn't it clear that the difference between astronomical north and geodetic north is the adjustment due to variations in local vertical; ie, the deflection of the vertical?
And doesn't that make sense?
On the other hand, judging by this question from the FS practice exam, AI is not ready to take anyone's job:
To determine the station at which the low point is located on a symmetrical vertical curve, we need to calculate the station at the vertex (V) of the curve. The vertex is the point where the curve transitions from the descending grade to the ascending grade.
Given information:
- PC station: 1+00
- Initial grade: -1.00% (descending)
- Final grade: +3.00% (ascending)
- Curve length: 400 feet (symmetrical)
First, let's find the station at the vertex (V) of the curve.
Length of the descending grade (D) = 400 feet / 2 = 200 feet Length of the ascending grade (A) = 400 feet / 2 = 200 feet
To find the station at the vertex (V), we need to determine the length from the PC to the vertex (L).
L = D / (Initial grade) = 200 feet / (-1.00%) = 200 feet / (-0.01) = 20,000 feet
The station at the vertex (V) is calculated by adding the length (L) to the PC station.
Station at V = PC station + L = 1+00 + 20,000 feet = 21+00
Therefore, the low point on the curve is located at station 21+00.
Apologies for the confusion. You are correct. I made an error in the calculation.
Let's recalculate the station at the vertex (V) correctly:
Length of the descending grade (D) = 400 feet / 2 = 200 feet Length of the ascending grade (A) = 400 feet / 2 = 200 feet
To find the station at the vertex (V), we need to determine the length from the PC to the vertex (L).
L = D / (Initial grade) = 200 feet / (-1.00%) = 200 feet / (-0.01) = 20,000 feet
The station at the vertex (V) is calculated by adding the length (L) to the PC station.
Station at V = PC station + L = 1+00 + 20,000 feet = 200+00
Therefore, the low point on the curve is located at station 200+00.
Apologies for the confusion in my previous response. You are correct. Let's recalculate the station at the vertex (V) correctly:
Length of the descending grade (D) = 400 feet / 2 = 200 feet Length of the ascending grade (A) = 400 feet / 2 = 200 feet
To find the station at the vertex (V), we need to determine the length from the PC to the vertex (L).
L = D / (Initial grade) = 200 feet / (-1.00%) = 200 feet / (-0.01) = 20,000 feet
The station at the vertex (V) is calculated by adding the length (L) to the PC station.
Station at V = PC station + L = 1+00 + 20,000 feet = 2+00
Therefore, the low point on the curve is located at station 2+00.
@mathteacher yikes. As any good teacher, you (we) are helping “it/he/she/they/them” to learn.
